9/8/98 AC 43.13-1B

CHAPTER 8. ENGINES, FUEL, EXHAUST, AND PROPELLERS

SECTION 1. ENGINES

8-1. GENERAL. Consult the manufac- pencil mark has not turned to a grayish-white turer’s manuals, service bulletins, and instruc- or ash color. This is the cold . tion books regarding the repair and overhaul, inspection, installation, and maintenance of (2) The probable cause of the cold cyl- aircraft engines, for that particular make, inder is either a defective or igni- model, and type of engine. This section lists tion lead. Switch spark plugs to another cylin- acceptable inspection and repair procedures der and run the test again. If the problem stays that may be used in the absence of an engine with the original cylinder, the problem is either manufacturer’s maintenance information. the ignition lead or the magneto.

8-2. SPECIAL INSPECTION. A visual b. Engine Sudden Stoppage In- inspection is needed to determine the condition spection. Sudden stoppage is a very rapid and of the engine and its components. An annual complete stoppage of the engine. It can be or 100-hour inspection should include the en- caused by engine seizure or by one or more of gine and nacelle group as follows. the blades striking an object in such a way that rpm goes to zero in less than one a. Cold Cylinder Check. If an engine is complete revolution of the propeller. Sudden running rough the cause may be a bad ignition stoppage can cause internal damage to con- lead, a spark plug not firing, a partially clogged stant-speed propellers; reduction drive; gear fuel injector, or a bad magneto. The dead cyl- train damage in the accessory section; crank- inder will be colder than the surrounding cyl- shaft misalignment; or damage to accessories inders and can be quickly determined by using such as magnetos, generators, vacuum pumps, the recommended cold cylinder checks. This and tach generators. should be done using a thermocouple probe which is very sensitive to small differences in (1) Every engine that suffers a sudden temperature, which is the case with a partially- stoppage must be inspected in accordance with clogged injector. For a carbureted engine, the the manufacturer’s maintenance instructions following check may be helpful: before being returned to service.

(1) Using experienced personnel, run (2) If the engine manufacturer does not the engine on the bad magneto for approxi- provide the required information, then the en- mately 30 seconds at 1200 rpm. Without gine case must be opened and every major switching the magneto switch back to both component part must be inspected using visual shut off the engine. Have another mechanic and/or nondestructive inspection (NDI) proce- use a grease pencil (non-carbon), and quickly dures as applicable. mark each exhaust stack approximately 1 inch from the flange that holds the exhaust stack to (3) The sudden-stoppage inspections the cylinder. Next, check the exhaust stacks include: checking for cowling, , and and look for the exhaust stack whose grease airframe cracks and hidden damage; and alignment of the engine mount to the airframe,

Par 8-1 Page 8-1 AC 43.13-1B 9/8/98 the mounting hardware, isolation mounts, and particular attention to the propeller thrust- bushings. The aircraft’s firewall must also be bearing area of the nose case section. checked for distortion, cracks, and elongated bolt holes. The damaged propeller must be (8) Inspect cylinders and cylinder hold- sent to an FAA-certificated repair station for down area for cracks and oil leaks. Thor- complete NDI and repair. oughly investigate any indication of cracks, oil leaks, or other damage. (4) Engine accessories such as: magne- tos, starters, fuel pumps, , alter- d. Internal Inspection Requirements. nators, or generators must be inspected in ac- cordance with the manufacturer’s maintenance (1) On engines equipped with crank- manual on sudden stoppage or overhaul proce- shaft vibration dampers, remove and inspect dures to determine the product’s airworthiness. the cylinders, and inspect the damp- ers in accordance with the engine manufac- c. (Direct Drive). turer’s inspection and overhaul manual. When Preliminary inspection before tear down. engine design permits, remove the damper pins, and examine the pins and damper liners (1) Remove the engine cowling and ex- for signs of nicks or brinelling. amine the engine for visible external damage and audible internal damage. (2) After removing the engine-driven accessories, remove the accessory drive case (2) Rotate the propeller shaft to deter- and examine the accessory and mine any evidence of abnormal grinding or drive gear train, couplings, and drive case for rubbing sounds. evidence of damage.

(3) With the propeller removed, inspect (a) Check for cracks in the case in the crankshaft flange or splines for signs of the area of accessory mount pads and gear twisting, cracks, or other deformation. Re- shaft bosses. move the thrust-bearing nut and seal and thor- oughly inspect the threaded area of the shaft (b) Check the gear train for signs of for evidence of cracks. cracked, broken, or brinelled teeth.

(4) Rotate the shaft slowly in 90-degree (c) Check the accessory drive shaft increments while using a dial indicator or an couplings for twisted splines, misalignment, equivalent instrument to check the concentric- and run-out. ity of the shaft. (d) Check connecting rods for cracks (5) Remove the oil sump drain plug and and straightness. check for metal chips and foreign material. e. Reciprocating Engine (Gear-Drive). (6) Remove the oil screens and inspect Inspect the engine, propeller, (refer to section 4 for metal particles and contamination. on propeller inspection), and components as described in the preceding paragraphs. (7) Visually inspect engine case exterior for signs of oil leaks and cracks. Give (1) Remove the propeller reduction gear housing and inspect for:

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(a) Loose, sheared, or spalled cap h. Accessory and Drive Inspection. screws or bolts. Check the drive shaft of each accessory, i.e., magnetos, generators, external , (b) Cracks in the case. and pumps for evidence of damage.

(2) Disassemble the gear train and in- 8-3. CRANKSHAFT INSPECTION AND spect the propeller shaft, reduction gears and REPAIR REQUIREMENTS. Carefully in- accessory drive gears for nicks, cracks, or spect for misalignment and replace if bent be- spalling. yond the manufacturer’s permissible service limit. Worn journals may be repaired by re- f. Engine-Mount Inspection. grinding in accordance with manufacturers’ in- structions. It is recommended that grinding (1) Examine the engine flex mounts operations be performed by appropriately-rated when applicable, for looseness of engine to repair stations or the original engine manufac- mount, distortion, or signs of wear. turer. Common errors that occur in crankshaft grinding are the removal of nitrided journal (2) Inspect the engine-mount structure surface, improper journal radii, unsatisfactory for bent, cracked, or buckled tubes. surfaces, and grinding tool marks on the jour- nals. If the fillets are altered, do not reduce (3) Check the adjacent airframe struc- their radii. Polish the reworked surfaces to as- ture firewall for cracks, distortion, or wrinkles. sure removal of all tool marks. Most opposed engines have nitrided , and engine (4) Remove engine-mount bolts and manufacturers specify that these crankshafts mount hold-down bolts and replace. must be re-nitrided after grinding.

g. Exhaust-driven Supercharger NOTE: Rapid deceleration or mo- (Turbo) Inspection. Sudden stoppage of the mentary slowing of a propeller may powerplant can cause the heat in turbine parts occur due to contact with tall grass, to heat-soak the turbine seals and bearings. water, or snow. If this occurs, the en- This excessive heat causes carbon to develop gine and propeller should be inspected in the seal area and varnish to form on the tur- in accordance with the manufac- bine bearings and journals. turer’s instruction or service bulletins.

(1) Inspect all air ducts and connections 8-4. REPLACEMENT PARTS IN CER- for air leaks, warpage, or cracks. TIFICATED ENGINES. Engine replacement parts must be approved under Title 14 of the (2) Remove compressor housing and Code of Federal Regulations (14 CFR), check the turbine wheel for rubbing or binding, part 21. Serviceable parts obtained from the and coke or varnish buildup. engine manufacturer, authorized service facil- ity, and those which are approved Federal NOTE: Turbine turbo supercharger Aviation Administration (FAA)/Parts Manu- disk seal rubbing is not unusual and facture Approval (PMA), or Technical Stan- may be a normal condition. Consult dard Order (TSO), and meet the requirements the engine manufacturer’s inspection of part 21 are acceptable for use as replace- procedures and table of limits. ment parts. Used engine parts can be installed

Par 8-2 Page 8-3 AC 43.13-1B 9/8/98 if that part either conforms to new part toler- 8-7. CYLINDER HOLD-DOWN NUTS ances or meets the manufacturer’s service lim- AND CAP SCREWS. Great care is required its. Ensure that used parts are airworthy and in tightening cylinder hold-down nuts and cap properly identified as a PMA or TSO part. screws. They must be tightened to recom- mended torque limits to prevent improper 8-5. OIL SYSTEM LINES INSPECTION. stressing and to ensure even loading on the The inspection of the plumbing for an oil sys- cylinder flange. The installation of baffles, tem is similar to the inspection of any other brackets, clips, and other extraneous parts un- plumbing system. The tubing, hose, tube fit- der nuts and cap screws is not a good practice tings, hose fittings, hose clamps, and all other and is discouraged. If these baffles, brackets, components of the system are inspected for etc., are not properly fabricated or made of cracks, holes, dents, bulges, and other signs of suitable material, they may cause loosening of damage that might restrict the oil flow or cause the nuts or cap screws even though the nuts or a leak. All lines are inspected to ensure that cap screws were properly tightened and locked they are properly supported and are not rub- at installation. Improper pre-stressing or loos- bing against a structure. Fittings should be ening of any one of these nuts or cap screws checked for signs of improper installation, will introduce the danger of progressive stud over-torquing, excessive tension, or other con- failure with the possible loss of the engine ditions which may lead to failure. cylinder in flight.

8-6. OIL FILTER INSPECTION. The oil 8-8. REUSE OF SAFETYING DEVICES. filter provides an excellent method for discov- Do not use cotter pins and safety wire a second ering internal engine damage. During the in- time. Flat, steel-type wrist pin retainers and spection of the engine oil filter, the residue on lock washers, likewise, must be replaced at the screens, disks, or disposable filter cartridge overhaul unless the manufacturer’s recom- and the residue in the filter housing are care- mendations permit their reuse. fully examined for metal particles. A new en- gine or a newly-overhauled engine will often 8-9. SELF-LOCKING NUTS FOR AIR- have a small amount of fine metal particles in CRAFT ENGINES AND ACCESSORIES. the screen or filter, but this is not considered Self-locking nuts may be used on aircraft en- abnormal. After the engine has been operated gines provided the following criteria are met: for a time and the oil has been changed one or more times, there should not be an appreciable a. When their use is specified by the en- amount of metal particles in the oil screen. If gine manufacturer in the assembly drawing, an unusual residue of metal particles is found parts list, and bills of material. in the oil screen, the engine must be taken out of service and disassembled to determine the b. When the nuts will not fall inside the source of the particles. As an additional pre- engine should they loosen and come off. caution, an oil analysis/trend analysis may pre- vent an engine failure in flight. c. When there is at least one full thread At oil changes, oil samples are often taken and protruding beyond the nut. sent to laboratories to be analyzed for wear by determining the amount of metal in the sam- d. Where the temperature will not ex- ple. Over time, a trend is developed and the ceed the maximum limits established for the engine can be removed from service before self-locking material used in the nut. On many failure.

Page 8-4 Par 8-4 9/8/98 AC 43.13-1B engines the cylinder baffles, rocker box covers, factory; however, engineering evaluation of the drive covers and pads, and accessory and su- details for the processes used should be ob- percharger housings are fastened with fiber in- tained. sert lock nuts which are limited to a maximum temperature of 250 °F. Above this tempera- a. Dense chromium plating of the crank- ture, the fiber insert will usually char and, con- pin and main journals of some small engine sequently, lose its locking characteristic. For crankshafts has been found satisfactory, except locations such as the exhaust pipe attachment where the crankshaft is already marginal in to the cylinder, a locknut which has good strength. Plating to restore worn, low-stress locking features at elevated temperatures will engine parts, such as accessory drive shafts give invaluable service. In a few instances, fi- and splines, propeller shaft ends, and seating ber insert lock nuts have been approved for use surfaces of roller and ball-type bearing races is on cylinder hold-down studs. This practice is acceptable but requires compliance with not generally recommended, since especially FAA-approved data. tight stud fits to the crankcase must be pro- vided, and extremely good cooling must pre- b. Porous chromium-plated walls of vail so that low temperatures exist where the cylinder barrels have been found to be satis- nut is installed. factory for practically all types of engines. Dense or smooth chromium plating, without e. Information concerning approved roughened surfaces on the other hand, has not self-locking nuts and their use on specific en- been found to be satisfactory. gines are usually found in engine manufac- turer’s manuals or bulletins. If the desired in- (1) Cylinder barrel pre-grinding and formation is not available, it is suggested that chromium plating techniques used by the the engine manufacturer be contacted. military are considered acceptable for all en- gines, and military-approved facilities engaged f. Refer to Chapter 7, Aircraft Hardware, in doing this work in accordance with military Control Cables, and Turnbuckles, for addi- specifications are eligible for approval by the tional information on self-locking nuts. FAA.

8-10. METALLIZING. Metallizing inter- (2) Chromium-plated cylinder barrels nal parts of aircraft engines is not acceptable have been required for some time to be identi- unless it is proven to the FAA that the metal- fied in such a manner that the markings are lized part will not adversely affect the airwor- visible with the cylinder installed. Military- thiness of the engine. Metallizing the finned processed cylinders are banded with orange surfaces of steel cylinder barrels with alumi- enamel above the mounting flange. It has been num is acceptable, since many engines are the practice to etch on either the flange edge or originally manufactured in this manner. on the barrel skirt the processor’s initials and the cylinder oversize. Most plating facilities 8-11. PLATING. Before restoring the plat- use the orange band as well as the permanent ing on any engine part in accordance with the identification marks. manufacturer’s instructions, the part should be visually inspected and have an NDI performed (3) A list of engine and maximum per- before any cylinder reconditioning. In general, missible cylinder barrel oversize are referenced chromium plating would not be applied to in table 8-1. highly-stressed engine parts. Certain applica- tions of this nature have been found to be satis-

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TABLE 8-1. Current engine and maximum permissible might possibly promote corrosive action. (Re- cylinder barrel oversize. fer to Chapter 6, Corrosion, Inspection, and Max. Protection.) Engine manufacturer Engine series oversize (in.) 8-13. ENGINE RUN-IN. After an aircraft Air Cooled Motors No oversize for (Franklin) sleeved cylinders. engine has been overhauled, it is recom- Solid cylinders...... 0.017 mended that the pertinent Continental Motors R-670, W-670, 0.010 to R9A.... 0.020 manufacturer’s run-in instructions be followed. 0.005 Observe the manufacturer’s recommendations GTSIO-520, 550...... 0.015 All others...... concerning engine temperatures and other cri- Jacobs All...... 0.015 teria. Repair processes employed during over- Kinner All...... 0.015 Pigman, LeBlond, All...... 0.025 haul often necessitate amending the manufac- Rearwin, Ken turer’s run-in procedures. Follow the ap- Royce Lycoming All...... 0.010 to proved amended run-in procedures in such in- 0.020 Menasco All...... 0.010 stances. Pratt & Whitney R-2800B, C, CA, CB.. 0.025 *R-959 and R-1830.... 0.030 All others...... 0.020 NOTE: Do not run up engines on the Ranger 6-410 early cyls. 0.010 ground for long periods of time with 6-390 6-410 late cyls. 6-440 0.120 the cowling off. The engine will over- (L-440) series.. heat because cylinder cooling has been Warner All...... 0.015 Wright All...... 0.020 disrupted. *(The above oversize limits correspond to the manufacturer’s requirements, except for P&W R-985 and R-1830 series engines.) 8-14. COMPRESSION TESTING OF AIRCRAFT ENGINE CYLINDERS. A test NOTE: ( Check for latest manufacturer specifications.) to determine the internal condition of the com- bustion chamber cylinder assembly by ascer- (4) Cylinder barrels which have been taining if any appreciable internal leakage is plated by an agency whose process is approved occurring is compression testing of aircraft en- by the FAA and which have not been worked gine cylinders. If a cylinder has less than a beyond maximum permissible limits, will be 60/80 reading on the differential test gauges on considered acceptable for installation on certi- a hot engine, and procedures in para- ficated engines. It will be the responsibility of graphs 8-15b(5)(i) and (j) fail to raise the com- the owner or the repairing agency to provide pression reading, the cylinder must be removed this proof. In some cases, it may be necessary and inspected. To determine the cylinder’s to remove cylinders to determine the amount problem area, have someone hold the propeller of oversize since this information may be at the weak cylinder’s top dead center and with etched on the mating surface of the cylinder compressed air still being applied, listen. If air base flange. is heard coming out of the exhaust pipe, the cylinder’s exhaust-valve is not seating prop- 8-12. CORROSION. Accomplish corrosion erly. If air is heard leaking out of the air preventive measures for temporary and long- cleaner/ heat box, the intake valve is term storage in accordance with the instruc- leaking. With the oil dipstick removed, and air tions issued by the pertinent engine manufac- is rushing out, the piston rings are defective. turer. Avoid the use of solutions which con- Remove and repair/overhaul the defective tain strong caustic compounds and all solu- cylinder. tions, polishes, cleaners, abrasives, etc., which

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a. Differential Compression Test. The (3) A typical schematic diagram of the most common type of compression tester cur- differential pressure tester is shown in rently in use is the differential pressure-type figure 8-1. tester. It provides a cross-reference to validate the readings obtained and tends to assure that the cylinder is defective before it is removed. Before beginning a compression test, consider the following points:

(1) When the spark plugs are removed from the engine, identify them to coincide with the cylinder and location from which they were removed. Close examination of the plugs will reveal the actual operating conditions and aid in diagnosing problems within each individual cylinder.

(2) The operating and maintenance rec- ords of the engine should be reviewed. Rec- ords of previous compression tests are of as- sistance in determining progressive wear con- ditions and help to establish the necessary maintenance corrective actions.

b. Differential Pressure Compression Test. The differential pressure tester is de- signed to check the compression of aircraft en- gines by measuring the leakage through the cylinders caused by worn or damaged compo- FIGURE 8-1. Schematic of differential pressure com- nents. The operation of the compression tester pression tester. is based on the principle that, for any given air- flow through a fixed orifice, a constant pres- (4) As the regulated air pressure is ap- sure drop across that orifice will result. The plied to one side of the restrictor orifice with restrictor orifice dimensions in the differential the air valve closed, there will be no leakage pressure tester should be sized for the particu- on the other side of the orifice and both pres- lar engine as follows: sure gauges will read the same. However, when the air valve is opened and leakage (1) For an engine cylinder having less through the cylinder increases, the cylinder than a 5.00-inch ; 0.040-inch orifice di- pressure gauge will record a proportionally ameter; .250 inch long; and a 60-degree ap- lower reading. proach angle. (5) While performing the check the (2) For an engine cylinder with 5.00 following procedures are listed to outline the inch bore and over: 0.060 inch orifice diame- principles involved, and are intended to sup- ter, .250 inch long, 60 degree approach angle. plement the manufacturer’s instructions for the particular tester being used.

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(a) Perform the compression test as (h) Open the air valve completely. soon as possible after the engine is shut down Check the regulated pressure and readjust, if to ensure that the piston rings, cylinder walls, necessary, to read 80 psi. and other engine parts are well-lubricated. (i) Observe the pressure indication of (b) Remove the most accessible the cylinder pressure gauge. The difference spark plug from each cylinder. between this pressure and the pressure shown by the regulator pressure gauge is the amount (c) With the air valve closed, apply of leakage through the cylinder. A loss in ex- an external source of clean air (approximately cess of 25 percent of the input air pressure is 100 to 120 psi) to the tester. cause to suspect the cylinder of being defec- tive; however, recheck the readings after oper- (d) Install an adapter in the spark ating the engine for at least 3 minutes to allow plug bushing and connect the compression for sealing of the rings with oil. tester to the cylinder. (j) If leakage is still occurring after a (e) Adjust the pressure regulator to recheck, it may be possible to correct a low obtain a reading of 20 psi on the regulator reading. This is accomplished by placing a fi- pressure gauge. At this time, the cylinder ber drift on the directly over the pressure gauge should also register 20 psi. valve stem and tapping the drift several times with a hammer to dislodge any foreign mate- (f) Turn the crankshaft, by hand, in rial between the valve face and seat. the direction of rotation until the piston (in the cylinder being checked) is coming up on its NOTE: When correcting a low read- compression . Slowly open the air valve ing in this manner, rotate the propel- and pressurize the cylinder to 80 psi. ler so the piston will not be at TDC. This is necessary to prevent the valve CAUTION: Care must be exercised from striking the top of the piston in in opening the air valve since suffi- some engines. Rotate the engine be- cient air pressure will have built up in fore rechecking compression to reseat the cylinder to cause it to rapidly ro- the valves in the normal manner. tate the propeller if the piston is not at top dead center (TDC). 8-15. SPARK PLUGS. The spark plug pro- vides the high-voltage electrical spark to ignite (g) Continue rotating the engine the fuel/air mixture in the cylinder. The types against this pressure until the piston reaches of spark plugs used in different engines will TDC. Reaching TDC is indicated by a flat vary with regard to heat range, reach, thread spot or sudden decrease in force required to size, and other characteristics required by the turn the crankshaft. If the crankshaft is rotated particular installation. too far, back up at least one-half revolution and start over again to eliminate the effect of a. Heat Range. The heat range of a spark backlash in the valve operating mechanism and plug is the principal factor governing aircraft to keep piston rings seated on the lower ring performance under various service conditions. lands. The term “heat range” refers to the

Page 8-8 Par 8-14 9/8/98 AC 43.13-1B classification of spark plugs according to their operate as hot as possible at low speeds and ability to transfer heat from the firing end of light loads and as cool as possible under the spark plug to the . cruising and takeoff power. Plug performance, therefore, depends on the operating tempera- (1) Spark plugs have been classified as ture of the insulator nose, with the most desir- “hot,” “normal,” and “cold.” However, these able temperature range falling between terms may be misleading because the heat 1,000 °F and 1,250 °F (538 °C and 677 °C). range varies through many degrees of tem- perature from extremely hot to extremely cold. (4) Fundamentally, an engine which Thus the words “hot,” “cold,” and “normal” do runs hot requires a relatively cold spark plug, not necessarily tell the whole story. whereas an engine which runs cool requires a relatively hot spark plug. If a hot spark plug is (2) Since the insulator is designed to be installed in an engine which runs hot, the spark the hottest part of the spark plug, its tempera- plug tip will be overheated and cause pre- ture can be related to the pre-ignition and ignition. If a cold spark plug is installed in an fouling regions as shown in figure 8-2. Pre- engine which runs cool, the tip of the spark ignition is likely to occur if surface areas in the plug will collect unburned carbon, causing combustion chamber exceed critical limits or if fouling of the plug. The principal factors gov- the spark plug core nose temperature exceeds erning the heat range of aircraft spark plugs 1,630 °F (888 °C). However, fouling or short- are: circuiting of the plug due to carbon deposits is likely to occur if the insulator tip temperature (a) the distance between the copper drops below approximately 800 °F (427 °C). sleeve around the insulator and the insulator Since spark plugs must operate between fairly tip; well-defined temperature limits, they must be supplied in various heat ranges to meet the re- (b) the thermal conductivity of the quirements of different engines under a variety insulating material; of operating conditions. (c) the thermal conductivity of the electrode;

(d) the rate of heat transfer between the electrode and the insulator;

(e) the shape of the insulator tip;

(f) the distance between the insulator tip and the shell; and

(g) the type of outside gasket used.

FIGURE 8-2. Chart of spark plug temperature ranges. (5) “Hot” plugs have a long insulator (3) From the engineering standpoint, nose; thereby, creating a long heat transfer each individual plug must be designed to offer path, whereas “cold” plugs have a relatively the widest possible operating range. This short insulator to provide a rapid transfer of means that a given type of spark plug should heat to the cylinder head. (See figure 8-3.)

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c. Installation Procedures. When in- stalling spark plugs, observe the following procedure.

(1) Visually inspect the plug for clean- liness and condition of the threads, ceramic, and electrodes.

NOTE: Never install a spark plug which has been dropped and always use new gaskets every time you install a spark plug. FIGURE 8-3. Hot and cold spark plugs. (2) Check the plug for the proper gap b. Reach. The spark plug reach (see fig- setting, using a round wire feeler gauge as ure 8-4) is the threaded portion which is in- shown in figure 8-5. In the case of used plugs, serted into the spark plug bushing of the cylin- procedures for cleaning and regapping are usu- der. A plug with the proper reach will ensure ally contained in the various manufacturers’ that the electrode end inside the cylinder is in manuals. the best position to achieve ignition. Spark plug seizure or improper combustion within the cylinder will probably occur if a plug with the wrong reach is used. Shell threads of spark plugs are classified as 14- or 18-mm spark plug diameter, long reach or short reach, thus:

Diameter Long reach Short reach 14 mm 1/2 in (12.7 mm) 3/8 in (9.53 mm) 18 mm 13/16 in. (20.64 mm) 1/2 in (12.7 mm)

FIGURE 8-5. Method of checking spark plug gap.

(3) Check the plug and cylinder bushing to ascertain that only one gasket is used per spark plug. When a thermocouple-type gasket is used, no other gasket is required.

(4) Apply anti-seize compound spar- ingly to the shell threads, but do not allow the compound to contact the electrodes since the FIGURE 8-4. Spark plug reach. material is conductive and will short out the

Page 8-10 Par 8-15 9/8/98 AC 43.13-1B plug. If desired, the use of anti-seize com- 8-16. OPERATIONAL PROBLEMS. pound may be eliminated on engines equipped Whenever problems develop during engine with stainless steel spark plug bushings or operation, which appear to be caused by the inserts. , it is recommended that the spark plugs and ignition harnesses be checked (5) Screw the plug into the cylinder first before working on the magnetos. The head as far as possible by hand. If the plug following are the more common spark plug will not turn easily to within two or three malfunctions and are relatively easy to iden- threads of the gasket, it may be necessary to tify. clean the threads. a. Fouling. NOTE: Cleaning inserts with a tap is not recommended as permanent dam- (1) Carbon fouling (see figure 8-6) is age to the insert may result. identified by the dull black, sooty deposits on the electrode end of the plug. Although the (6) Seat the proper socket securely on primary causes are excessive ground idling and the spark plug and tighten to the torque limit rich idle mixtures, a cold heat range may also specified by the engine manufacturer before be a contributing factor. proceeding to the next plug. (2) Lead fouling is characterized by CAUTION: A loose spark plug will hard, dark, cinder-like globules which gradu- not transfer heat properly, and during ally fill up the electrode cavity and short out engine operation, may overheat to the the plug. (See figure 8-6a.) The primary cause point the nose ceramic will become a for this condition is poor fuel vaporization “hot spot” and cause pre-ignition. combined with a high tetraethyl-lead content However, avoid over-tightening as fuel. A cold heat range may also contribute to damage to the plug and bushing may this condition. result. (3) Oil fouling is identified by a wet, (7) Connect the ignition lead after wip- black carbon deposit over the entire firing end ing clean with a dry, lint-free cloth. Insert the of the plug as shown in figure 8-6b. This con- terminal assembly into the spark plug in a dition is fairly common on the lower plugs in straight line. (Care should be taken as im- horizontally-opposed engines, and both plugs proper techniques can damage the terminal in the lower cylinders of radial engines. Oil sleeves.) Screw the connector nut into place fouling is normally caused by oil drainage past until finger tight, then tighten an additional the piston rings after shutdown. However, one quarter turn while holding the elbow in the when both spark plugs removed from the same proper position. cylinder are badly fouled with oil and carbon, some form of engine damage should be sus- (8) Perform an engine run-up after in- pected, and the cylinder more closely in- stalling a new set of spark plugs. When the spected. Mild forms of oil fouling can usually engine has reached normal operating tempera- be cleared up by slowly increasing power, tures, check the magnetos and spark plugs in while running the engine until the deposits are accordance with the manufacturer’s instruc- burned off and the misfiring stops. tions.

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FIGURE 8-6a. Typical lead-fouled spark plug. FIGURE 8-6. Typical carbon-fouled spark plug. (2) Corrosive gases formed by combus- b. Fused Electrodes. There are many dif- tion and the high voltage spark have eroded the ferent types of malfunctions which result in electrodes. Spark plugs in this condition re- fused spark plug electrodes; however, most are quire more voltage to fire—often more than associated with pre-ignition either as the cause the ignition system can produce. (See fig- or the effect. For this reason, any time a spark ure 8-6d.) plug is found with the following defects, fur- ther investigation of the cylinder and piston c. Bridged Electrodes. Occasionally, free should be conducted. combustion chamber particles will settle on the electrodes of a spark plug and gradually bridge (1) Occasionally, the ceramic nose core the electrode gap, resulting in a shorted plug. will crack, break away, and remain trapped be- Small particles may be dislodged by slowly hind the ground electrode. This piece of insu- cycling the engine as described for the oil- lation material will then buildup heat to the fouled condition; however, the only remedy for point it will ignite the fuel/air mixture prema- more advanced cases is removal and replace- turely. The high temperatures and pressures ment of the spark plug. This condition is encountered during this condition can cause shown in figure 8-6e. damage to the cylinder and piston and ulti- mately lead to fusing and shorting out of the plug. (See figure 8-6c.)

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FIGURE 8-6b. Typical oil-fouled spark plug. FIGURE 8-6c. Typical spark plug with cracked d. Metal Deposits. Whenever metal spray core nose. is found on the electrodes of a spark plug, it is e. Flashover. It is important that spark an indication that a failure of some part of the plug terminal contact springs and moisture engine is in progress. The location of the cyl- seals be checked regularly for condition and inder in which the spray is found is important cleanliness to prevent “flashover” in the con- in diagnosing the problem, as various types of nector well. Foreign matter or moisture in the failures will cause the metal spray to appear terminal connector well can reduce the insula- differently. For example, if the metal spray is tion value of the connector to the point the ig- located evenly in every cylinder, the problem nition system voltages at higher power settings will be in the induction system, such as an im- may flash over the connector well surface to peller failure. If the metal spray is found only ground and cause the plug to misfire. If on the spark plugs in one cylinder, the problem moisture is the cause, hard starting can also re- is isolated to that cylinder and will generally sult. The cutaway spark plug shown in fig- be a piston failure. ure 8-7 illustrates this malfunction. Any spark In view of the secondary damage which occurs plug found with a dirty connector well may whenever an engine part fails, any preliminary have this condition, and should be recondi- indication such as metal spray should be thor- tioned before reuse. oughly investigated to establish and correct the cause.

Par 8-16 Page 8-13 AC 43.13-1B CHG 1 9/27/01

FIGURE 8-6d. Typical worn out spark plug.

FIGURE 8-6e. Typical spark plug with bridged electrodes. 8-17. SPARK PLUG PRE-RECONDI- TIONING INSPECTION. All spark plugs should be inspected visually before recondi- tioning to eliminate any plug with obvious de- fects. A partial checklist of common defects includes:

a. Chipped or cracked ceramic either at the nose core or in the connector well. FIGURE 8-7. Spark plug well flashover. b. Damaged or badly worn electrodes. 8-18. IGNITION HARNESSES INSPEC- c. Badly nicked, damaged, or corroded TION. Aircraft-quality ignition harness is threads on shell or shielding barrel. usually made of either medium or high- d. Dented, bent, or cracked shielding temperature wire. The type used will depend barrel. upon the manufacturing specification for the particular engine. In addition to the applicable e. Connector seat at the top of the manufacturer’s maintenance and repair proce- shielding barrel badly nicked or corroded. dures, the following is a quick-reference

Page 8-14 Par 8-19 9/27/01 AC 43.13-1B CHG 1 checklist for isolating some of the malfunc- function quickly. However, conduct any inter- tions inherent to ignition harnesses. nal inspection or repair of a magneto in accor- dance with the manufacturer’s maintenance a. Carefully inspect the lead conduit or and overhaul manuals. shielding. A few broken strands will not affect serviceability, but if the insulation in general a. Inspect the distributor block contact looks worn, replace the lead. springs. If broken or corroded, replace.

b. When replacing a lead, if the dressing b. Inspect the felt oil washer, if applica- procedure is not accomplished properly, ble. It should be saturated with oil. If it is dry, strands of shielding may be forced through the check for a worn bushing. conductor insulation. If this occurs, a short will exist in the conductor; therefore, it is es- c. Inspect the distributor block for sential this task be performed properly. cracks or a burned area. The wax coating on the block should not be removed. Do not use c. The high-temperature coating used any solvents for cleaning. on some lightweight harnesses is provided for vibration abrasion resistance and moisture protection. Slight flaking or peeling of this coating is not serious, and a harness assembly need not be removed from service because of this condition.

d. Check the spark plug contact springs for breaks, corrosion, or deformation. If pos- sible, check the lead continuity from the dis- tributor block to the contact spring. FIGURE 8-8. Typical method of clamping leads. e. Check the insulators at the spark plug end of the lead for cracks, breaks, or evidence d. Look for excess oil in the breaker of old age. Make sure they are clean. compartment. If oil is present, it may indicate a bad oil seal or bushing at the drive end. This f. Check to see that the leads are posi- condition could require complete overhaul, as tioned as far away from the too much oil may foul and cause excessive as possible and are supported to prevent any burning of the contact points. whipping action. e. Look for frayed insulation on the leads in the breaker compartment of the mag- g. When lightweight harnesses are used neto. See that all terminals are secure. Be sure and the conduit enters the spark plug at a se- that wires are properly positioned. vere angle, use clamps as shown in figure 8-8 to prevent overstressing the lead. f. Inspect the capacitor visually for gen- eral condition, and check the mounting bracket 8-19. MAGNETO INSPECTION. When- for cracks or looseness. If possible, check the ever ignition problems develop and it is deter- capacitor for leakage, capacity, and series re- mined that the magneto is the cause of the dif- sistance. ficulty, the following are a few simple inspec- tion procedures which may locate the mal-

Par 8-16 Page 8-15 AC 43.13-1B 9/8/98

g. Examine the points for excessive wear or burning. Discard points which have deep pits or excessively burned areas. Desired contact surfaces have a dull gray, sandblasted (almost rough) or frosted appearance over the area where electrical contact is made. Fig- ure 8-9 shows how the normal contact point will look when surfaces are separated for in- spection. Minor irregularities or roughness of point surfaces are not harmful (see fig- FIGURE 8-11. Point with well-defined mound. ure 8-10), neither are small pits or mounds, if not too pronounced. If there is a possibility of CAUTION: When inspecting the con- the pit becoming deep enough to penetrate the tact points for condition, do not open pad (see figure 8-11), reject the contact assem- further than absolutely necessary. bly. Excess tension on the spring will weaken it and adversely affect the performance of the magneto.

i. Adjustment of magneto point gaps must be correct for proper internal timing of a magneto. See applicable manufacturer’s pub- lications for internal timing procedures.

FIGURE 8-9. Normal contact point. j. Check the breaker cam to assure cleanness and smoothness. Check the cam screw for tightness. If new points have been installed, blot a little oil on the cam. In addi- tion, check contact point assembly to ascertain that the cam follower is securely fastened.

k. If the impulse coupling is accessible, inspect for excessive wear on the contact edges of the body and flyweights. In addition, check the flyweights for looseness on the axles.

FIGURE 8-10. Point with minor irregularities. l. Further examination of the impulse coupling body may disclose cracks caused by h. Generally, no attempt should be exceedingly-tight flyweight axle rivets. made to dress or stone contact point assem- blies; however, if provided, procedures and m. Check the magneto ventilators for limits contained in the manufacturer’s manuals proper functioning and obstructions. If drilled may be followed. plugs are used, they should be in the lowest vent hole of the magneto to serve as a drain for condensation and oil.

Page 8-16 Par 8-19 9/8/98 AC 43.13-1B

8-20. MAGNETO-TO-ENGINE TIMING. c. Recheck magneto-to-engine timing While the actual process of timing magnetos to after any point-gap adjustment, or after re- an engine is covered in the engine manufac- placement of the breaker points. turer’s technical manuals, the following gen- eral procedures may be applied. d. Never advance the magneto timing beyond the engine timing specification rec- a. Before installing a new magneto, the ommended by the engine manufacturer. correct “E” gap setting specified by the mag- neto manufacturer should be verified. e. The possibility of a timing error ex- ists if a timing indicator which attaches to the b. When setting or checking the mag- propeller shaft or spinner of geared engines is neto-to-engine timing, always turn the crank- used. Engine timing specifications are always shaft steadily in the normal direction of rota- given in degrees of crankshaft travel and can- tion to eliminate any error caused by gear not be applied directly to geared propeller backlash. shafts because of the gear ratio. Therefore, the correct position of the propeller shaft, if used for timing, must be determined by multiplying the crankshaft timing angle in degrees before top center (BTC) by the propeller gear ratio.

8-21.8-29. [RESERVED.]

Par 8-20 Page 8-17 (and 8-18)

9/8/98 AC 43.13-1B

SECTION 2. FUEL SYSTEMS

8-30. GENERAL. Maintain, service, and d. Bonding. Bond metallic fuel lines at adjust aircraft fuel systems and fuel system each point where they are clamped to the components in accordance with the applicable structure. Integrally bonded and cushioned manufacturer’s maintenance instructions. line support clamps are preferred to other Certain general fuel system maintenance prin- clamping and bonding methods. ciples are outlined in the following para- graphs.. e. Support of Line Units. To prevent possible failure, all fittings heavy enough to 8-31. FUEL LINES AND FITTINGS. cause the line to sag should be supported by When fuel system lines are to be replaced or means other than the tubing. repaired, consider the following fundamentals in addition to the applicable airworthiness re- f. Support clamps. quirements. Additional inspection and repair practices for aircraft tubing systems may be (1) Place support clamps or brackets for found in the Chapter 9, Aircraft Systems and metallic lines as follows. Components. Approximate Tube O.D. distance between a. Compatibility of Fittings. All fittings supports are to be compatible with their mating parts. 1/8”-3/16”------9” Although various types of fittings appear to be 1/4”-5/16”------12” interchangeable in many cases they have dif- 3/8”-1/2”------16” ferent thread pitch or minor design differences 5/8”-3/4”------22” 1”-1 1/4”------30” which prevent proper mating and may cause 1 1/2”-2”------40” the joint to leak or fail. (2) Locate clamps or brackets as close b. Routing. Make sure that the line does to bends as possible to reduce overhang. (See not chafe against control cables, airframe figure 8-12.) structure, etc., or come in contact with electri- cal wiring or conduit. Where physical separa- 8-32. FUEL TANKS AND CELLS. tion of the fuel lines from electrical wiring or Welded or riveted fuel tanks that are made of conduit is impracticable, locate the fuel line commercially pure aluminum, 3003, 5052, or below the wiring and clamp it securely to the similar alloys, may be repaired by welding. airframe structure. In no case should wiring be Tanks made from heat-treatable aluminum al- supported by the fuel line. loys are generally assembled by riveting. In case it is necessary to rivet a new piece in a c. Alignment. Locate bends accurately so tank, use the same material as used in the tank that the tubing is aligned with all support undergoing repair, and seal the seams with a clamps and end fittings and is not drawn, compound that is insoluble in gasoline. Spe- pulled, or otherwise forced into place by them. cial sealing compounds are available and Never install a straight length of tubing be- should be used in the repair of tanks. Inspect tween two rigidly-mounted fittings. Always fuel tanks and cells for general condition, secu- incorporate at least one bend between such fit- rity of attachment, and evidence of leakage. tings to absorb strain caused by vibration and Examine fuel tank or cell vent line, fuel line, temperature changes. and sump drain attachment fittings closely.

Par 8-30 Page 8-19 AC 43.13-1B 9/8/98

c. Removal of Flux After Welding. It is especially important, after repair by welding, to completely remove all flux in order to avoid possible corrosion. Promptly upon completion of welding, wash the inside and outside of the tank with liberal quantities of hot water and then drain. Next, immerse the tank in either a 5 percent nitric or 5 percent sulfuric acid solu- tion. If the tank cannot be immersed, fill the tank with either solution, and wash the outside with the same solution. Permit the acid to re- main in contact with the weld about one hour and then rinse thoroughly with clean water. Test the efficiency of the cleaning operation by applying some acidified 5 percent silver nitrate solution to small quantity of the rinse water used last to wash the tank. If a heavy white precipitate is formed, the cleaning is insuffi- FIGURE 8-12. Location of clamps at tube bends. cient and the washing should be repeated. CAUTION: Purge de-fueled tanks of explosive fuel/air mixtures in accor- d. Flexible Fuel Cells. Inspect the inte- dance with the manufacturer’s service rior for checking, cracking, porosity, or other instructions. In the absence of such signs of deterioration. Make sure the cell re- instructions, utilize an inert gas such taining fasteners are properly positioned. If repair or further inspection is required, follow as CO2 as a purgative to assure the to- tal deletion of fuel/air mixtures. the manufacturer’s instructions for cell re- moval, repair, and installation. Do not allow a. Integral Tanks. Examine the interior flexible fuel cells to dry out. Preserve them in surfaces and seams for sealant deterioration accordance with the manufacturer’s instruc- and corrosion (especially in the sump area). tions. Follow the manufacturer’s instructions for re- pair and cleaning procedures. 8-33. FUEL TANK CAPS, VENTS, AND OVERFLOW LINES. Inspect the fuel tank b. Internal Metal Tanks. Check the ex- caps to determine they are the correct type and terior for corrosion and chafing. Dents or size for the installation, and that “O” rings are other distortion, such as a partially-collapsed in good condition. tank caused by an obstructed fuel tank vent, can adversely affect fuel quantity gauge accu- a. Unvented caps, substituted for vented racy and tank capacity. Check the interior sur- caps, will cause fuel starvation and possible faces for corrosion. Pay particular attention to collapse of the fuel tank or cell. Malfunction- the sump area, especially for those of which ing of this type occurs when the pressure sumps are made of cast material. Repairs to within the tank decreases as the fuel is with- the tank may be accomplished in accordance drawn. Eventually, a point is reached where with the practices outlined in the chapter 4, the fuel will no longer flow, and/or the outside Metal Structure, Welding and Brazing of this atmospheric pressure collapses the tank. Thus, AC.

Page 8-20 Par 8-32 9/8/98 AC 43.13-1B the effects will occur sooner with a full fuel c. Selector Handles. Check the operation tank than with one partially filled. of each handle or control to see that it indicates the actual position of the selector valve to the b. Check tank vents and overflow lines placard location. Movement of the selector thoroughly for condition, obstructions, correct handle should be smooth and free of binding. installation, and proper operation of any check Assure that stops and detents have positive ac- valves and protection units. Pay particular tion and smooth operational feel. Worn or attention to the location of the tank vents when missing detents and stops can cause unreliable such information is provided in the manufac- positioning of the fuel selector valve. turer’s service instructions. Inspect for cracked or deteriorated filler opening recess d. Worn Linkage. Inaccurate positioning drains, which may allow spilled fuel to accu- of fuel selector valves can also be caused by mulate within the wing or fuselage. One worn mechanical linkage between the selector method of inspection is to plug the fuel line at handle and the valve unit. An improper fuel the outlet and observe fuel placed in the filler valve position setting can seriously reduce en- opening recess. If drainage takes place, inves- gine power by restricting the available fuel tigate condition of the line and purge any ex- flow. Check universal joints, pins, gears, cess fuel from the wing. splines, cams, levers, etc., for wear and exces- sive clearance which prevent the valve from c. Assure that filler opening markings positioning accurately or from obtaining fully are affixed to, or near, the filler opening; “off” and “on” positions. marked according to the applicable airworthi- ness requirements; and are complete and legi- e. Assure that required placards are ble. complete and legible. Replace those that are missing or cannot be read easily. 8-34. FUEL CROSS-FEED, FIREWALL SHUTOFF, AND TANK SELECTOR 8-35. FUEL PUMPS. Inspect, repair, and VALVES. Inspect these valves for leakage overhaul boost pumps, emergency pumps, and proper operation as follows. auxiliary pumps, and engine-driven pumps in accordance with the appropriate manufac- a. Internal leakage can be checked by turer’s instructions. placing the appropriate valve in the “off” posi- tion, draining the fuel strainer bowl, and ob- 8-36. FUEL FILTERS, STRAINERS, serving if fuel continues to flow into it. Check AND DRAINS. Check each strainer and filter all valves located downstream of boost pumps element for contamination. Determine and with the pump(s) operating. Do not operate correct the source of any contaminants found. the pump(s) longer than necessary. Replace throw-away filter elements with the recommended type. Examine fuel strainer b. External leakage from these units can bowls to see that they are properly installed ac- result in a severe fire hazard, especially if the cording to the direction of the fuel flow. unit is located under the cabin floor or within a Check the operation of all drain devices to see similarly-confined area. Correct the cause of that they operate properly and have positive any fuel stains associated with fuel leakage. shutoff action.

Par 8-33 Page 8-21 AC 43.13-1B 9/8/98

8-37. INDICATOR SYSTEMS. Inspect, c. Open fuel lines must be capped. service, and adjust the fuel indicator systems according to the manufacturer’s instructions. d. Fire-extinguishing equipment must Determine that the required placards and in- always be available. strument markings are complete and legible. e. Metal fuel tanks must not be welded or 8-38. FUEL SYSTEM PRECAUTIONS. soldered unless they have been adequately In servicing fuel systems, remember that fuel purged of fuel fumes. Keeping a tank or cell is flammable and that the danger of fire or ex- filled with carbon dioxide will prevent explo- plosion always exists. The following precau- sion of fuel fumes. tions should be taken: f. Do not use Teflon tape on any fuel a. Aircraft being serviced or having the lines to avoid getting the tape between the flare fuel system repaired must be properly and fitting, which can cause fluid leaks. grounded. 8-39.8-44. [RESERVED.] b. Spilled fuel must be neutralized or re- moved as quickly as possible.

Page 8-22 Par 8-37 9/8/98 AC 43.13-1B

SECTION 3. EXHAUST SYSTEMS

8-45. GENERAL. Any exhaust system fail- ure should be regarded as a severe hazard. Depending upon the location and type of fail- ure, it can result in carbon monoxide (CO) poi- soning of crew and passengers, partial or com- plete engine power loss, or fire. Exhaust sys- tem failures generally reach a maximum rate of occurrence at 100 to 200 hours’ operating time, and over 50 percent of the failures occur within 400 hours.

8-46. MUFFLER/HEAT EXCHANGER FAILURES. Approximately one-half of all exhaust system failures are traced to cracks or ruptures in the heat exchanger surfaces used for cabin and carburetor air heat sources.

a. Failures in the heat exchanger’s sur- face (usually the muffler’s outer wall) allow exhaust gases to escape directly into the cabin heat system. The failures are, for the most part, attributed to thermal and vibration fatigue cracking in the areas of stress concentration; e.g., tailpipe and stack, inlet-attachment areas. (See figures 8-13 through 8-16.) FIGURE 8-13. Typical muffler wall fatigue failure at ex- haust outlet. (A. Complete muffler assembly with heat b. Failures of the spot welds which at- shroud removed; B. Detail view of failure.) tach heat transfer pins, as shown in fig- ure 8-14A, can result in exhaust gas leakage. enter the cabin via defective or inadequate In addition to the CO hazard, failure of heat seals at firewall openings, wing strut fittings, exchanger surfaces can permit exhaust gases to doors, and wing root openings. Mani- be drawn into the engine induction system and fold/stack failures, which account for ap- cause engine overheating and power loss. proximately 20 percent of all exhaust system failures, reach a maximum rate of occurrence 8-47. MANIFOLD/STACK FAILURES. at about 100 hours’ operating time. Over Exhaust manifold and stack failures are also 50 percent of the failures occur within usually fatigue-type failures which occur at 300 hours. welded or clamped joints; e.g., stack-to-flange, stack-to-manifold, muffler connections, or 8-48. INTERNAL MUFFLER FAIL- crossover pipe connections. Although these URES. Internal failures (baffles, diffusers, failures are primarily a fire hazard, they also etc.) can cause partial or complete engine present a CO problem. Exhaust gases can power loss by restricting the flow of the ex- haust gases. (See figures 8-17 through 8-20.)

Par 8-45 Page 8-23 AC 43.13-1B 9/8/98

FIGURE 8-14. Typical muffler wall failure. (A. Complete muffler assembly with heat shroud removed; B. Detail view of failure; C. Cross section of failed muffler.)

As opposed to other failures, erosion and - expected, the time required for these failures to bonizing caused by the extreme thermal con- develop is longer than that for fatigue failures. ditions are the primary causes of internal fail- Internal muffler failures account for nearly ures. Engine after-firing and combustion of 20 percent of the total number of exhaust sys- unburned fuel within the exhaust system are tem failures. probable contributing factors. b. The highest rate of internal muffler a. In addition, local hot spot areas failures occurs between 500 and 750 hours of caused by uneven exhaust gas flow, result in operating time. Engine power loss and exces- burning, bulging, and rupture of the outer muf- sive back-pressure caused by exhaust outlet fler wall. (See figure 8-14.) As might be blockage may be averted by the installation

Page 8-24 Par 8-48 9/8/98 AC 43.13-1B

FIGURE 8-17. Section of a muffler showing typical internal baffle failure.

FIGURE 8-15. Typical muffler wall fatigue failure. (A. Complete muffler assembly with heat shroud partially removed; B. Detailed view of failure.)

FIGURE 8-16. Typical fatigue failure of muffler end plate at stack inlet. FIGURE 8-18. Loose pieces of a failed internal baffle.

Par 8-48 Page 8-25 AC 43.13-1B 9/8/98 of an exhaust outlet guard as shown in fig- b. Remove or loosen all exhaust shields, ures 8-21a and 8-21b. The outlet guard may carburetor and cabin heater muffs, shrouds, be fabricated from a 3/16-inch stainless steel heat blankets, etc., required to permit inspec- welding rod. tion of the complete system.

Form the rod into two “U” shaped segments, c. Perform necessary cleaning opera- approximately 3 inches long and weld onto the tions and inspect all external surfaces of the exhaust tail pipe as shown in figure 8-21b so exhaust system for cracks, dents, and missing that the guard will extend 2 inches inside the parts. Pay particular attention to welds, exhaust muffler outlet port. Installation of an clamps, supports and support attachment lugs, exhaust outlet guard does not negate the im- bracing, slip joints, stack flanges, gaskets, portance of thorough inspection of the internal flexible couplings, and etc. (See figures 8-22 parts of the muffler or the necessity of replac- and 8-23.) Examine the heel of each bend, ar- ing defective mufflers. eas adjacent to welds, any dented areas, and low spots in the system for thinning and pitting 8-49. INSPECTION. Inspect exhaust sys- due to internal erosion by combustion products tems frequently to ascertain complete system or accumulated moisture. An ice pick (or integrity. similar pointed instrument) is useful in probing suspected areas. Disassemble the system as CAUTION: Marking of exhaust sys- necessary to inspect internal baffles or diffus- tem parts. Never use lead pencils, ers. carbon based pencils, etc., to mark exhaust system parts. Carbon depos- d. Should a component be inaccessible ited by those tools will cause cracks for a thorough visual inspection or hidden by from heat concentration and carboni- non-removable parts, remove the component zation of the metal. If exhaust system and check for possible leaks by plugging its parts must be marked, use chalk, openings, applying approximately 2 psi inter- Prussian blue, India ink, or a grease nal pressure, and submerging it in water. Any pencil that is carbon-free. leaks will cause bubbles that can be readily detected. Dry thoroughly before reinstallation. a. Before any cleaning operation, re- move the cowling as required to expose the 8-50. REPAIRS. It is generally recom- complete exhaust system. Examine cowling mended that exhaust stacks, mufflers, tail- and nacelle areas adjacent to exhaust system pipes, and etc., be replaced with new or recon- components for telltale signs of exhaust gas ditioned components rather than repaired. soot indicating possible leakage points. Check Welded repairs to exhaust systems are compli- to make sure no portion of the exhaust system cated by the difficulty of accurately identifying is being chafed by cowling, engine control ca- the base metal so that the proper repair materi- bles, or other components. The exhaust sys- als can be selected. Changes in composition tem often operates at red-hot temperatures of and grain structure of the original base metal 1,000 °F or more; therefore, parts such as ig- further complicates the repair. However, when nition leads, hoses, fuel lines, and flexible air welded repairs are necessary, follow the gen- ducts, should be protected from radiation and eral procedures outlined in Chapter 4; Metal convection heating by heat shields or adequate Structure, Welding, and Brazing; of this AC. clearance. Retain the original contours and make sure that

Page 8-26 Par 8-48 9/8/98 AC 43.13-1B

FIGURE 8-19. Failed internal baffle partially obstructing the muffler outlet.

FIGURE 8-21a. Example of exhaust outlet guard.

FIGURE 8-21b. Example of exhaust outlet guard installed.

FIGURE 8-20. Failed internal baffle completely ob- temperature self-locking nuts for brass or spe- structing the muffler outlet. cial high-temperature locknuts used by the manufacturer. Never reuse old gaskets or old the completed repair has not warped or other- star lock washers. When disassembly is neces- wise affected the alignment of the exhaust sary replace gaskets with new ones of the same system. Repairs or sloppy weld beads, which type provided by the manufacturer. protrude internally, are not acceptable since they cause local hotspots and may restrict ex- 8-51. TURBO-SUPERCHARGER. When haust gas flow. All repairs must meet the a turbo-supercharger is included, the exhaust manufacturer’s specifications. When repairing system operates under greatly-increased pres- or replacing exhaust system components, be sure and temperature conditions. Extra pre- sure that the proper hardware and clamps are cautions should be taken in the exhaust used. Do not substitute steel or low- system’s care and maintenance. During

Par 8-50 Page 8-27 AC 43.13-1B 9/8/98

FIGURE 8-22. Effect of improperly positioned exhaust pipe/muffler clamp. high-altitude operation, the exhaust system pressure is maintained at, or near, sea level values. Due to the pressure differential, any leaks in the system will allow the exhaust gases to escape with a torch-like intensity that can severely damage adjacent structures. A common cause of turbo-supercharger mal- function is coke deposits (carbon buildup) in the waste gate unit causing erratic system op- eration. Excessive deposit buildups may cause the waste gate valve to stick in the closed po- sition, causing an overboost condition. Coke deposit buildup in the turbo-supercharger itself FIGURE 8-23. Primary inspection areas. will cause a gradual loss of power in flight and low deck pressure reading before takeoff. Ex- overall condition. Regardless of whether or perience has shown that periodic decoking, or not the augmentor tubes contain heat ex- removal of carbon deposits, is necessary to changer surfaces, they should be inspected for maintain peak efficiency. Clean, repair, over- cracks along with the remainder of the exhaust haul, and adjust turbo-supercharger system system. Cracks can present a fire or CO haz- components and controls in accordance with ard by allowing exhaust gases to enter nacelle, the applicable manufacturer’s instructions. wing, or cabin areas.

8-52. AUGMENTOR SYSTEMS. Inspect 8-53.8-70. [RESERVED.] augmentor tubes periodically for proper align- ment, security of attachment, and general

Page 8-28 Par 8-51 9/27/01 AC 43.13-1B CHG 1

SECTION 4. REPAIR OF METAL PROPELLERS

8-71. GENERAL. Reject damaged blades removal of an excessive amount of metal, local with model numbers which are on the manu- etching should be accomplished at intervals facturer’s list of blades that cannot be repaired. during the process of removing suspected Follow the propeller manufacturer’s recom- scratches. Upon completion of the repair, mendations in all cases, and make repairs in carefully inspect the entire blade by etching or accordance with latest techniques and best in- anodizing. Remove all effects of the etching dustry practices. process with fine emery paper. Blades identi- fied by the manufacturer as being cold-worked NOTE: Title 14 of the Code of Fed- (shot-blasted or cold-rolled) may require eral Regulations, 14 CFR, part 65 does peening after repair. Accomplish repair and not allow an airframe and power peening operations on this type of blade in ac- plant mechanic to perform major re- cordance with the manufacturer’s instructions. pairs to propellers. However, it is not permissible in any case to peen down the edges of any injury wherein the 8-72. STEEL BLADES. Due to the critical operation will lap metal over the injury. effects of surface injuries and their repair on the fatigue life of steel blades, all repairs must a. Flaws in Edges. Round out nicks, be made in accordance with the manufacturer’s scars, cuts, etc., occurring on the leading edge instructions. of aluminum-alloy blades as shown in fig- ure 8-24 (view B). Blades that have the lead- 8-73. ALUMINUM PROPELLER RE- ing edges pitted from normal wear in service PAIRS. Aluminum-alloy propellers and may be reworked by removing sufficient mate- blades with dents, cuts, scars, scratches, nicks, rial to eliminate the pitting. In this case, re- leading-edge pitting, etc., may be repaired, move the metal by starting a sufficient distance provided the removal or treatment does not from the edge, as shown in figure 8-25, and materially affect the strength, weight, or per- working forward over the edge in such a way formance of the blade. Remove these damages that the contour will remain substantially the or otherwise treat as explained below, unless it same, avoiding abrupt changes in contour. is contrary to the manufacturer’s instructions Trailing edges of blades may be treated in sub- or recommendations. More than one injury is stantially the same manner. On the thrust and not sufficient cause alone for rejection of a camber face of blades, remove the metal blade. A reasonable number of repairs per around any dents, cuts, scars, scratches, nicks, blade may be made and not necessarily result and pits to form shallow saucer-shaped depres- in a dangerous condition, unless their location sions as shown in figure 8-24 (view C). Exer- with respect to each other is such to form a cise care to remove the deepest point of the continuous line of repairs that would materi- injury and also remove any raised metal ally weaken the blade. Suitable sandpaper or around the edges of the injury as shown in fig- fine-cut files may be used for removing the ure 8-24 (view A). When repairing blades, necessary amount of metal. In each case, the figures 8-26 and 8-27 show the maximum re- area involved will be smoothly finished with duction in width and thickness that is allow- #00 sandpaper or crocus cloth, and each blade able below the minimum dimensions required from which any appreciable amount of metal by the blade drawing and blade manufacturing has been removed will be properly balanced specification. Beyond the 90 before it is used. Etch all repairs. To avoid

Par 8-71 Page 8-29 AC 43.13-1B CHG 1 9/27/01

FIGURE 8-24. Method of repairing surface scratches, nicks, etc., on aluminum-alloy propellers.

FIGURE 8-25. Correct and incorrect method of reworking leading edge of aluminum-alloy propellers.

Page 8-30 Par 8-73 9/8/98 AC 43.13-1B

90 percent blade radius point, the blade width straightening of blades to permit shipment to a and thickness may be modified as per the certificated propeller repair facility may result manufacturer’s instructions. in hidden damage not being detected and an unairworthy propeller being returned to serv- b. Shortening Blades. Shortening pro- ice. peller blades is a major repair. When the re- moval or treatment of defects on the tip neces- 8-74. REPAIR LIMITS. The following sitates shortening a blade, shorten each blade limits are those listed in the blade manufac- used with it and keep such sets of blades to- turing specification for aluminum-alloy blades gether. (See figure 8-26 for acceptable meth- and govern the width and thickness of new ods.) Mark the shortened blades to correspond blades. These limits are to be used with the with the manufacturer’s system of model des- pertinent blade drawing to determine the ignation to indicate propeller diameter. In minimum original blade dimensions to which making the repair, it is not permissible to re- the reduction of figure 8-27 and figure 8-28. duce the propeller diameter below the mini- may be applied. When repairs reduce the mum diameter limit shown on the pertinent width or thickness of the blade below these specification or type certificate data sheet. limits, reject the blade. The face alignment or track of the propeller should fall within the c. Straighten Propeller Blades. Never limits recommended by the manufacturer for straighten a damaged propeller. Even partial new propellers

FIGURE 8-26. Method of repairing damaged tip of aluminum-alloy propellers.

Par 8-73 Page 8-31 AC 43.13-1B 9/8/98

a. No repairs are permitted to the shanks (r1) is 24 in. from the shank and the original, (roots or hub ends) of aluminum-alloy, adjust- as manufactured, blade width (w) at the repair able-pitch blades. The shanks must be within location is 1.88 in. manufacturer’s limits. (a) Step 1. Calculate the blade radius b. The following two examples show (r) how to determine the allowable repair limits on aluminum alloy blades. r = d/2 = (10 ft 6 in)/2 = 126/2 = 63 in.

(1) Example 1. Determine the blade (b) Step 2. Calculate percent of width repair allowable (∆w) and minimum blade radius to repair (r%) blade width limit, (w1) for a blade having a di- ameter (d) of 10 ft. 6 in. The repair location r% = r1/r x 100 = (24/63) x 100 = 38

a. Draw a vertical line at the value of r% = 38 on the horizontal axis. b. Where the vertical line intersects the curve, draw a horizontal line to the right to intersect the vertical axis. c. Read the percent reduction in width (∆w%) on the vertical axis at this intersection. ∆w% = 2.5

FIGURE 8-27. Example 1. Determine the repair width limits.

Page 8-32 Par 8-74 9/8/98 AC 43.13-1B

(c) Step 3. Determine percent reduc- 8-75. STEEL HUBS AND HUB PARTS. tion in width (∆w%) from figure 8-27. Repairs to steel hubs and parts must be ac- complished only in accordance with the manu- (d) Step 4. Calculate the blade width facturer’s recommendations. Welding and repair allowable (∆w) remachining is permissible only when covered by manufacturer’s service bulletins (SB). ∆w =(∆w%) x (w) x(0.01) = (2.5) x (1.88) x (0.01) = 0.05 in. 8-76. PROPELLER HUB AND FLANGE REPAIR. When the fixed-pitch propeller bolt (e) Step 5. Calculate the minimum holes in a hub or crankshaft become damaged blade width limit (w1) at the repair location or oversized, it is permissible to make repairs by using methods (A) or (B) in figure 8-29, or by use of aircraft standard bolts 1/16-inch w1 = w - ∆w = 1.88 - 0.05 = 1.83 in. larger than the original bolts. Make the repairs (2) Example 2. Determine the blade in accordance with the recommendations of the thickness repair allowable (∆t) and minimum propeller metal hub manufacturer or the engine manufacturer, as applicable. Obtain from the blade thickness limit (t1) for a blade having a diameter (d) of 10 ft. 6 in. The repair location engine or propeller hub manufacturer suitable flange bushings with threaded or smooth (r1) is 43 in. from the shank and the original, as manufactured, blade thickness (t) at the re- bores, as illustrated in methods (A) or (B) of pair location is 0.07 in. figure 8-29. Drill the flange and insert the bushings as recommended by the propeller to (a) Step 1. Calculate the blade radius accommodate the bushings, and protect the (r) holes with 2 coats of aluminum paint or other high moisture-resistant coating. Use bolts of r = d/2 = (10 ft 6 in)/2 = 126/2 = 63 in. the same size as those originally used. Any of the following combinations may be used: (b) Step 2. Calculate percent of (1) drilled head bolt and castellated nut, blade radius to repair (r%) (2) drilled head bolt and threaded bushing, or (3) undrilled bolt and self-locking nut. Where r% = r/r x 100 = (43/63) x 100 = 68 it is desirable to use oversized bolts, obtain suitable aircraft-standard bolts 1/16-inch larger (c) Step 3. Determine percent reduc- than the original bolts. Enlarge the crankshaft tion in thickness (∆t%) from figure 8-28. propeller flange holes and the propeller hub holes sufficiently to accommodate the new bolts without more than 0.005-inch clearance. (d) Step 4. Calculate the blade Such reboring will be permitted only once. thickness repair allowable (∆t) Further repairs of bolt holes may be in accor- dance with the methods listed in (A) or (B) of ∆t = (∆t%) x (t) (0.01) = (4.0) x (0.07) x (0.01) figure 8-29. = 0.003 in. NOTE: Method (A) or (B) is pre- (e) Step 5. Calculate the minimum ferred over the oversized bolt method, blade thickness limit (t ) at the repair location 1 because a propeller hub flange re- drilled in accordance with this latter t1 = t - ∆t = 0.07 - 0.003 = 0.067 in.

Par 8-74 Page 8-33 AC 43.13-1B 9/8/98

a. Draw a vertical line at the value of r% = 68 on the horizontal axis. b. Where the vertical line intersects the curve, draw a horizontal line to the right to inter- sect the vertical axis. c. Read the percent reduction in thickness (∆t%) on the vertical axis intersection ∆t% = 4.0

FIGURE 8-28. Example 2. Determine the repair thickness limits.

method will always require the re- only those replacement parts which are ap- drilling of all new propellers subse- proved under 14 CFR, part 21 should be used. quently used with the re-drilled flange. 8-78. DEICING SYSTEMS. Components used in propeller deicing systems should be in- 8-77. CONTROL SYSTEMS. Components spected, repaired, assembled, and/or tested in used to control the operation of certificated accordance with the manufacturer’s recom- propellers should be inspected, repaired, as- mendations. Only those repairs which are sembled, and/or tested in accordance with the covered by the manufacturer’s recommenda- manufacturer’s recommendations. Only those tions should be made, and only those replace- repairs which are covered by the manufac- ment parts which are approved under turer’s recommendations should be made, and 14 CFR, part 21 should be used.

Page 8-34 Par 8-76 9/8/98 AC 43.13-1B

FIGURE 8-29. Repair of fixed-pitch hub and propeller with elongated or damaged bolt holes.

8-79.8-90. [RESERVED.]

Par 8-78 Page 8-35 (and 8-36)

9/8/98 AC 43.13-1B

SECTION 5. INSPECTION OF PROPELLERS

8-91. GENERAL. All propellers, regardless a. Fixed-pitch propellers are normally of the material from which they are made, removed from the engine at engine overhaul should be regularly and carefully inspected for periods. Whenever the propeller is removed, any possible defect. Any doubtful condition, visually inspect the rear surface for any indi- such as looseness of parts, nicks, cracks, cation of cracks. When any defects are found, scratches, bruises, or loss of finish should be disassemble the metal hub from the propeller. carefully investigated and the condition Inspect the hub bolts for wear and cracks at the checked against repair and maintenance speci- head and threads, and if cracked or worn, re- fications for that particular type of propeller. place with new equivalent bolts. Inspect for Any propeller that has struck a foreign object elongated bolt holes, enlarged hub bore, and during service should be promptly inspected for cracks inside the bore or anywhere on the for possible damage in accordance with the propeller. Repair propellers found with any of propeller manufacturer’s prescribed procedures these defects. If no defects are found, the pro- and, if necessary, repaired according to the peller may be reinstalled on the engine. Before manufacturer’s instructions. If the propeller is installation, touch up with varnish all places damaged beyond the repair limits established where the finish is worn thin, scratched, or by the propeller manufacturer, and a replace- nicked. Track and balance the propeller, and ment is necessary, install the same coat the hub bore and bolt holes with some make/model approved or alternate as specified moisture preventive such as asphalt varnish. in the equipment list, applicable FAA Aircraft In case the hub flange is integral with the Specification, Type Certificate Data Sheet crankshaft of the engine, final track the pro- (TCDS), or Supplemental Type Certificate peller after it is installed on the engine. In all (STC). A sample manufacturer’s propeller in- cases where a separate metal hub is used, make spection checklist is shown in table 8-2. It a final balance and track with the hub installed shows the items to be inspected and the in- on the propeller. spection intervals. b. On new, fixed-pitch propeller instal- 8-92. WOOD OR COMPOSITION PRO- lations, inspect the bolts for proper torque after PELLERS AND BLADES. Wood propellers the first flight and after the first 25 hours of are usually found on low-power, reciprocating flying. Thereafter, inspect and check the bolts engines while composition (Carbon fiber, for proper torque at least every 50 hours. No Kevlar) propellers are used on high horse- definite time interval can be specified, since a power reciprocating and turbine engines. Due bolt’s proper torque is affected by changes in to the nature of wood, these propellers should the wood caused by the moisture content of the be inspected frequently to assure airworthi- air where the airplane is flown and stored. ness. Inspect for defects such as cracks, dents, During wet weather, some moisture is apt to warpage, glue failure, delamination defects in enter the propeller wood through the holes the finish, and charring of the wood between drilled in the hub. The wood then swells, and the propeller and the flange due to loose pro- because expansion is limited by the bolts ex- peller mounting bolts. Composition propellers tending between the two flanges, some of the should be inspected in accordance with the wood fibers become crushed. Later, when the propeller manufacturer’s instructions. propeller dries out during dry weather or due

Par 8-91 Page 8-37 AC 43.13-1B 9/8/98

TABLE 8-2. Sample manufacturer’s propeller inspection checklist.

Nature of Inspection Engine Operating Hours

PROPELLER GROUP 50 100 500 1000

1. Inspect spinner and back plate for cracks...... 0 0 0 0 2. Inspect blades for nicks and cracks...... 0 0 0 0 3. Check for grease and oil leaks...... 0 0 0 0 4. Lubricate propeller per Lubrication Chart...... 0 0 0 0 5. Check spinner mounting Brackets for cracks...... 0 0 0 6. Check propeller mounting bolts and safety (Check torque if safety is broken)...... 0 0 0 7. Inspect hub parts for cracks and corrosion...... 0 0 0 8. Rotate blades of constant speed propeller and check for tightness in hub pilot tube...... 0 0 0 9. Remove constant speed propeller; remove sludge from propeller and crankshaft...... 0 0 10. Inspect complete propeller and spinner assembly for security, chafing, cracks, deterioration, wear and correct installation...... 0 0 0 11. Check propeller air pressure (at least once a month)...... 0 0 0 0 12. Overhaul propeller...... 0 to heat from the engine, a certain amount of occur at the threaded ends of the lag screws propeller hub shrinkage takes place, and the and may be an indication of internal cracking wood no longer completely fills the space be- of the wood. Check the tightness of the lag tween the two hub flanges. Consequently, the screws, which attach the metal sleeve to the hub bolts become loose. wood blade, in accordance with the manufac- turer’s instructions. Inspect and protect the c. In-flight tip failures may be avoided shank areas of composition blades next to the by frequent inspections of the metal cap, lead- metal sleeve in the same manner as that used ing edge strip, and surrounding areas. Inspect for wood blades. for such defects as looseness or slipping, sepa- ration of soldered joints, loose screws, loose 8-93. METAL PROPELLERS AND rivets, breaks, cracks, eroded sections, and cor- BLADES. These propellers and blades are rosion. Inspect for separation between the generally susceptible to fatigue failure result- metal leading edge and the cap, which would ing from the concentration of stresses at the indicate the cap is moving outward in the di- bottoms of sharp nicks, cuts, and scratches. It rection of centrifugal force. This condition is is necessary, therefore, to frequently and care- often accompanied by discoloration and loose fully inspect them for such injuries. Propeller rivets. Inspect the tip for cracks by grasping it manufacturers publish SB’s and instructions with the hand and slightly twisting about the which prescribe the manner in which these in- longitudinal blade centerline and by slightly spections are to be accomplished. Additional bending the tip backward and forward. If the information is also available in AC 20-37D, leading edge and the cap have separated, care- Aircraft Metal Propeller Maintenance. fully inspect for cracks at this point. Cracks usually start at the leading edge of the blade. a. Steel Blade Inspection. The inspection A fine line appearing in the fabric or plastic of steel blades may be accomplished by either may indicate a crack in the wood. Check the visual, fluorescent penetrant (see chapter 5), or trailing edge of the propeller blades for bond- magnetic particle inspection. The visual in- ing, separation, or damage. spection is easier if the steel blades are covered with engine oil or rust-preventive compound. d. Examine the wood close to the metal The full length of the leading edge, especially sleeve of wood blades for cracks extending near the tip, the full length of the trailing edge, outward on the blade. These cracks sometimes the grooves and shoulders on the shank, and all

Page 8-38 Par 8-92 9/8/98 AC 43.13-1B dents and scars should be examined with a unauthorized straightening of the blade. magnifying glass to decide whether defects are Sighting along the leading edge of a propeller scratches or cracks. blade for any signs of bending can provide evidence of unapproved blade straightening. b. Aluminum Propellers and Blades. Blades should be examined for any discolora- Carefully inspect aluminum propellers and tion that would indicate unauthorized heating. blades for cracks and other flaws. A trans- Blades that have been heated for any repair verse crack or flaw of any size is cause for re- must be rejected, since only cold straightening jection. Multiple deep nicks and gouges on the is authorized. All blades showing evidence of leading edge and face of the blade is cause for unapproved repairs should be rejected. When rejection. Use dye penetrant or fluorescent dye bent propellers are shipped to an approved re- penetrant to confirm suspected cracks found in pair facility for inspection and repair, the pro- the propeller. Refer any unusual condition or peller should never be straightened by field appearance revealed by these inspections to the service personnel to facilitate shipping, be- manufacturer. cause this procedure can conceal damage. Propeller tip damage will sometimes lead c. Limitations. maintenance personnel to consider removing damaged material from the blade tips. How- (1) Corrosion may be present on pro- ever, propellers are often manufactured with a peller blades in varying amounts. Before per- particular diameter to minimize vibration. forming any inspection process, maintenance Unless the TCDS and both the engine and pro- personnel must examine the specific type and peller manufacturers specifically permit short- extent of the corrosion. (See chapter 6, and/or ening of the blades on a particular propeller, refer to AC 43-4A, Corrosion Control For Air- any shortening of the blades would probably craft.) create an unairworthy condition. When condi- tions warrant, inspect the blade tips for evi- (2) Corrosion, other than small areas dence of shortening and, if necessary, measure (6 square inches or less) of light surface type the propeller diameter to determine if it has corrosion, may require propeller removal and been changed by an unauthorized repair. reconditioning by a qualified propeller repair facility. When intergranular corrosion is pres- 8-94. PROPELLER HUB. ent, the repair can be properly accomplished only by an appropriately certificated propeller a. Fixed Pitch. repair facility. Corrosion pitting under pro- peller blade decals should be removed as de- (1) Inspection procedures require re- scribed in the propeller manufacturer’s SB’s moval of the propeller spinner for examination and applicable airworthiness directives (AD). of the prop hub area. Cracks may be present in the hub area between or adjacent to bolt holes (3) Unauthorized straightening of blade, and along the hub pilot bore. Cracks in these following a ground strike or other damage, can areas cannot be repaired and require immediate create conditions that lead to immediate blade scrapping of the propeller. failure. These unapproved major repairs may sometimes be detected by careful inspection of (2) Propeller attach bolts should be ex- the leading edges and the flat face portion of amined for looseness or an unsafetied or the blade. Any deviation of the flat portion, cracked condition. Cracked or broken bolts such as bows or kinks, may indicate are usually the result of overtorquing. Correct

Par 8-93 Page 8-39 AC 43.13-1B 9/8/98 torquing procedures require all bolt threads to in the manner specified by the propeller manu- be dry, clean, and free of any lubrication be- facturer. On makes and models with a grease fore torquing. fitting on the hub, before greasing the hub re- move the grease fitting opposite the one to b. Controllable Pitch. which you are going to add grease. This will allow the excess grease and pressure to exit (1) Inspect controllable pitch propellers through the grease fitting hole rather than the frequently to determine that all parts are lubri- hub seal. cated properly. It is especially recommended that all lubrication be accomplished in accor- (6) Fiber-block, pitch-change mecha- dance with the propeller manufacturer’s in- nisms should be inspected for deterioration, fit, structions. and the security of the pitch-clamp forks.

(2) Complete inspection/servicing re- (7) Certain models of full-feathering quires the removal of the spinner for examina- propellers use spring-loaded pins to retain the tion and servicing of the propeller hub and feathered blade position. Spring and pin units blade clamp area. All inspections and servic- should be cleaned, inspected, and relubricated ing of the pitch control mechanism should per the manufacturer’s recommendations and follow the recommendations of the propeller, applicable AD’s. engine, and airframe manufacturers. Propel- lers must be in compliance with applicable (8) Pitch change counterweights on AD’s and manufacturer’s SB’s. blade clamps should be inspected for security, safety, and to ensure that adequate counter- (3) The hub, blade clamps, and pitch weight clearance exists within the spinner. change mechanisms should be inspected for corrosion from all sources, including rain, 8-95. INSPECTION. snow, and bird droppings that may have en- Due to the exceptionally high stresses that may tered through the spinner openings. Examine be generated by particular propeller/engine the hub area for oil and grease leaks, missing combinations at certain engine revolutions per grease-fitting caps, and leaking or missing minute (RPM), many propeller and aircraft grease fittings. manufacturers have established areas of RPM restrictions and other restrictions on maximum (4) Propeller domes should be checked RPM for some models. Some RPM limits do for leaks, both at the seals and on the fill valve not exceed 3 percent of the maximum RPM (if so equipped). The dome valve may be leak- permitted, and a slow-running tachometer can tested by applying soapy water over the fill cause an engine to run past the maximum valve end. Domes should be serviced only RPM limits. Since there are no post- with nitrogen or dry air in accordance with the manufacture accuracy requirements for engine manufacturer’s recommendations. When pro- , tachometer inaccuracy could lead peller domes are inspected and found filled to propeller failure, excessive vibration, or un- with oil, the propeller should be removed and scheduled maintenance. If the tachometer ex- inspected/repaired by an appropriately-rated ceeds 2 percent (plus or minus) of the tested repair facility. RPM, replace it.

(5) It is especially recommended that all 8-96.8-106. [RESERVED.] lubrication be accomplished at the periods and

Page 8-40 Par 8-94 9/8/98 AC 43.13-1B

SECTION 6. PROPELLER TRACKING AND VIBRATION

8-107. GENERAL. To ensure smooth 8-109. VIBRATION. Although vibration powerplant operations, first start with a prop- can be caused by the propeller, there are nu- erly-installed propeller. Each propeller should merous other possible sources of vibration be checked for proper tracking (blades rotating which can make troubleshooting difficult. in the same plane of rotation). Manufacturer’s recommendations should in all cases be a. If a propeller vibrates, whether due to followed. balance, angle, or track problems, it typically vibrates, throughout the entire RPM range, al- 8-108. PROPELLER TRACKING though the intensity of the vibration may vary CHECK. The following is a simple procedure with the RPM. If a vibration occurs only at that can be accomplished in less than one particular RPM or within a limited RPM 30 minutes: range (e.g. 2200-2350 RPM), the vibration is not normally a propeller problem but a prob- a. Chock the aircraft so it cannot be lem with a poor engine/propeller match. moved. b. If a propeller vibration is suspected b. Remove one spark plug from each but cannot be positively determined, if possi- cylinder. This will make the propeller easier ble, the ideal troubleshooting method is to and safer to turn. temporarily replace the propeller with one which is known to be airworthy and test fly the c. Rotate one of the blades so it is aircraft. pointing down. c. There are numerous allowable toler- d. Place a solid object (e.g. a heavy ances in blade angles, balance, track, and wooden block that is at least a couple of inches blade width and thickness dimensions. These higher off the ground than the distance be- tolerances have been established through many tween the propeller tip and the ground) next to years of experience. The degree to which the propeller tip so that it just touches (see fig- these factors affect vibration is sometimes dis- ure 8-30), or attach a pointer/indicator to the puted and can involve significant repair bills, cowling itself. which may or may not cure a vibration prob- lem. Reliance upon experienced, reputable e. Rotate the propeller slowly to see if propeller repair stations is the owner’s best the next blade “tracks” through the same point method of dealing with these problems. (touches the block/pointer). Each blade track should be within 1/16-inch (plus or minus) d. Blade shake is not the source of vibra- from the opposite blade’s track. tion problems. Once the engine is running, centrifugal force holds the blades firmly (ap- f. If the propeller is out of track, it may proximately 30-40,000 lbs.) against blade be due to one or more propeller blades being bearings. bent, a bent propeller flange, or propeller mounting bolts that are either over or under- e. Cabin vibration can sometimes be im- torqued. An out-of-track propeller will cause proved by reindexing the propeller to the vibration and stress to the airframe and engine, crankshaft. The propeller can be removed, and may cause premature propeller failure. rotated 180§, and re-installed.

Par 8-107 Page 8-41 AC 43.13-1B 9/8/98

f. The propeller spinner can be a con- This condition is normally caused by inade- tributing factor to an out-of-balance condition. quate shimming of the spinner front support or An indication of this would be a noticeable a cracked or deformed spinner. spinner “wobble” while the engine is running.

FIGURE 8-30. Propeller tracking (wood block or cowling fixture shown).

8-110.8-129. [RESERVED.]

Page 8-42 Par 8-109