INVESTIGATION REPORT www.bea.aero
(1 )One of the Accident to the PS-28 Cruiser investigators from the Swiss registered HB-WXA Transportation Safety Investigation Board on 5 July 2017
(STSB) was onboard (1) the aeroplane as at Colombier (Switzerland) instructor. In order to safeguard the impartiality of the Time 14:13(2) investigation, STSB chose to delegate Operator GVM Lausanne it to the BEA. Type of flight Training (2)Except where Persons onboard Student pilot and instructor otherwise indicated, times in this report Student pilot and instructor fatally injured, aeroplane Consequences and damage are in local time. destroyed This is a courtesy translation by the BEA of the Final Report on the Safety Investigation published in March 2020. As accurate as the translation may be, the original text in French is the work of reference.
Engine failure during initial climb, stall and spin, collision with ground, in training
1 - HISTORY OF THE FLIGHT The student pilot, accompanied by an instructor, departed from Lausanne-La Blécherette airport (Switzerland) bound for Neuchâtel aerodrome (Switzerland). On arriving at the aerodrome, he carried out three aerodrome traffic patterns before making a complete landing shortly before 14:00. After passing by the runway office, the student pilot and instructor got back into the plane. At 14:12, they took off from runway 05 for the return flight. During the initial climb, the aeroplane turned left, then the turn became steeper. The aeroplane entered a nose-down spin and crashed into a small wood bordering Neuchâtel lake, at around 600 m from the threshold of runway 23 of the aerodrome.
The BEA investigations are conducted with the sole objective of improving aviation safety and are not intended to apportion blame or liabilities.
1/12 BEA2017-0409.en/June 2020 Figure 1: Accident flight path
2 - ADDITIONAL INFORMATION 2.1 Instructor information The instructor, aged 34, had held a professional pilot licence since 8 June 2011 and the instructor rating since 12 May 2016. The day of the accident, he had logged 4,481 flight hours on aeroplanes, of which 103 hours as instructor.
2.2 Student pilot information The student pilot, aged 40, who was following practical training for the private pilot licence (PPL) had logged a flight time of 26 hours 45 minutes and 138 landings. All the flight hours had been carried out on the aeroplane involved in the accident. The student pilot carried out his first solo flight on 21 June 2017.
The BEA investigations are conducted with the sole objective of improving aviation safety and are not intended to apportion blame or liabilities.
2/12 BEA2017-0409.en/June 2020 2.3 Aircraft information 2.3.1 General
The PS-28 Cruiser was built by Czech Sport Aircraft. This aeroplane is classed in the LSA (Light Sport Aircraft) category and holds a restricted certificate of airworthiness. (3)European Aviation This CS-LSA type certificate, issued by EASA(3), specifies that the aeroplane can be equipped Safety Agency. with a certified engine or an uncertified engine. When it is equipped with an uncertified engine, the latter is certified as if forming part of the aeroplane. The aeroplane and engine are then certified as a whole. In this particular case, it is the aircraft manufacturer who provides the maintenance programme concerning the engine. The manufacturer generally takes the maintenance programme provided by the engine manufacturer. The aeroplane had been bought new by GVM Lausanne in April 2013. The PS-28 Cruiser registered HB-WXA was equipped with an uncertified Bombardier Rotax 912 ULS 2 4-cylinder (4)Cf. para. 2.7.3. engine(4). On the crew taking charge of the aeroplane, it had logged 1,493 operating hours and 4,997 landings. Various engine related problems had been reported and treated since April 2015. In particular, engine vibrations and power losses, notably during take-off, had been reported.
2.3.2 Climb speed and stall speed The flight manual indicates a best angle of climb speed of 55 kt and a best rate of climb speed of 62 kt. The flight manual also specifies the following stall speeds at maximum weight (600 kg):
flaps retracted: 37 kt; 1st flap detent position (12°): 35 kt; flaps fully extended (30°): 31 kt.
2.3.3 Aircraft manufacturer’s procedure in event of engine failure The engine failure after take-off procedure described in the aeroplane flight manual is the following:
(5)Knots-Indicated “1. Airspeed - maintain 60 KIAS(5) Air Speed 2. Flaps - as necessary 3. Fuel selector - OFF 4. Ignition switch - OFF 5. MASTER GEN - OFF 6. MASTER BAT - OFF - before landing 7. Land straight ahead, turning only to avoid obstacles. Note Altitude loss during 180° turn is approximately 400 ft.”
The BEA investigations are conducted with the sole objective of improving aviation safety and are not intended to apportion blame or liabilities.
3/12 BEA2017-0409.en/June 2020 2.4 Meteorological information The meteorological conditions were anticyclonic, the wind was calm, visibility above 10 km with no clouds. The temperature was 28 °C.
2.5 Aerodrome Information Neuchâtel aerodrome (LSGN) bordering the lake of the same name, is situated 7.5 km southwest of Neuchâtel, at an altitude of 435 m (1,427 ft). It has a 700 x 20 m paved runway
05/23 which is bordered by a 550 x 30 m grass runway. There is no air traffic control service at the aerodrome. The pilots transmit A/A messages on the frequency allocated to the aerodrome.
Figure 2: Neuchâtel aerodrome (LSGN) visual approach chart
The BEA investigations are conducted with the sole objective of improving aviation safety and are not intended to apportion blame or liabilities.
4/12 BEA2017-0409.en/June 2020 2.6 Witness statements The different witnesses reported having heard engine misfires before the engine noise stopped. The witnesses then heard a cracking noise but no-one saw the plane.
2.7 Technical Examinations 2.7.1 Examination of wreckage The examination of the wreckage of the PS-28 did not find any malfunction likely to explain the loss of control of the aeroplane. The flaps were set to 12°, in the take-off position.
(6)Electronic Flight 2.7.2 Read-out of parameters recorded in EFIS(6) and video from Neuchâtel Instrument System aerodrome webcam which displays instruments in The accident flight data was retrieved from the two EFIS equipping the instrument panel the cockpit of the aeroplane. The read-out of this data revealed a loss of engine power during the initial climb. This significant loss of power occurred at low height and suddenly: the engine rpm dropped from 5,100 rpm, the nominal rating used for take-off according to the flight manual, to 3,150 rpm, in less than ten seconds. The sampling of the “engine rating” parameter meant that it was not possible to precisely determine the time of the power decrease but the (7) The points examination of the altitude and speed parameters situated this failure at around point(7), correspond to Figure 1 and Figure at a point when the altitude was increasing while the speed was decreasing from 61 kt 3 of the report. to 54 kt. The aeroplane then started a left turn while continuing to climb (point), the pitch being kept above 5°. The left bank increased steadily while the pitch and vertical speed decreased quickly. The airspeed reached a minimum of 34 kt (point) and then the altitude started to quickly decrease. The aeroplane entered a nose-down spin before colliding with the ground. This spin is confirmed by the video recorded by the aerodrome surveillance camera.
The BEA investigations are conducted with the sole objective of improving aviation safety and are not intended to apportion blame or liabilities.
5/12 BEA2017-0409.en/June 2020 (8)Positive values correspond to a right bank. (8) Figure 3: Accident flight data
2.7.3 Examination of powerplant 2.7.3.1 Carburetors The engine is equipped with two Bing 64 carburetors. The carburetors are located on each side of the upper part of the engine, each one supplying its two neighbouring cylinders. Although the engine was damaged, they were in good condition. The figure below shows cross-section views of this carburetor.
Source: manufacturer maintenance manual Figure 4: carburetor cross-section The BEA investigations are conducted with the sole objective of improving aviation safety and are not intended to apportion blame or liabilities.
6/12 BEA2017-0409.en/June 2020 On this carburetor, the throttle valve is controlled in the cockpit. The fuel is metered by the movement of a carburetor piston equipped with a jet needle which slides in the needle jet. The higher the needle, the greater the quantity of fuel injected. The needle is equipped with a circlip associated with an O-ring. The circlip prevents the needle from coming out of the carburetor piston under gravity. At the top, the needle is held by a fixation screw (in orange on Figures No 4 and 5) screwed into the carburetor piston. This fixation screw is machined to accommodate the circlip, O-ring and needle. This type of assembly allows the circlip to remain integral with the needle. The end of the needle has several slots. These slots are used to assemble the circlip in various positions. The manufacturer specifies, for each engine, the nominal position of the circlip in order to adjust the fuel flow rate. The needle of the right carburetor was found separated from the circlip, wedged in the main jet. It was bent following a buckling phenomenon. The circlip and O-ring were found whole in the carburetor piston. This finding shows that the circlip had separated from the needle. This separation is only possible if the fixation screw is not screwed into the carburetor piston in a nominal way. The housing in the carburetor piston for the fixation screw was not damaged which could have explained why it was not nominally screwed in. Moreover, it was checked that this fixation screw could be screwed into the carburetor piston in a nominal way, it was found that this was possible. The following test was carried out after disassembly. The circlip (Figure 6) was put back in position on the needle, in the position specified by the manufacturer for the given engine. The circlip did not block on the needle, it slid freely. After this handling operation, the circlip suddenly broke. The mechanical properties of the circlip had deteriorated leading to its deformation and its loss of elasticity. The condition of the circlip suggests that the modification of its mechanical properties was not due to the accident. The O-ring (Figure 5) was not deformed. Circular marks only were identified on its inner perimeter. These marks were the consequence of the O-ring coming into contact with the edges of the different needle slots as it progressively separated.
The BEA investigations are conducted with the sole objective of improving aviation safety and are not intended to apportion blame or liabilities.
7/12 BEA2017-0409.en/June 2020
Figure 5: Circlip and O-ring Figure 6: Deformed needle blocked
recovered in the carburetor piston of in main jet of right carburetor the right carburetor
Figure 7: Needle with circlip and O-ring in position (left carburetor)
The deformation observed on the needle (Figure 6) is clearly the consequence of its separation from the carburetor piston. In these conditions, the carburetor was no longer functional. The engine would then only be operating with the two left cylinders as only the left carburetor was functional. This asymmetry leads to substantial vibrations.
2.7.3.2 Ignition system The ROTAX® 912 engine is equipped with a dual ignition unit of a breakeless, capacitor discharge design, with an integrated generator. The ignition unit needs no external power supply. The engine is equipped with eight spark plugs, two per cylinder. The integrated generator rotor, installed aft of the engine and driven in rotation by the crankshaft, has two charging coils, identified as 1 in the diagram below. These charging coils each supply an electronic module. The energy is stored in capacitors in each electronic module. The integrated generator stator also has four trigger coils (identified as 2 in Figure 8). At the moment of ignition, these trigger coils discharge the energy stored in the capacitors of the electronic modules to the ignition coils. There are four ignition coils, each supplying two spark plugs of two different cylinders. In the event of an electronic module failure, two ignition coils are no longer powered. In each cylinder, a single spark plug would then ensure the ignition, instead of the nominal two plugs.
The BEA investigations are conducted with the sole objective of improving aviation safety and are not intended to apportion blame or liabilities.
8/12 BEA2017-0409.en/June 2020 Source: manufacturer maintenance manual Figure 8: Ignition system diagram
The examination of the ignition system on the wreckage made it possible to establish the following points:
Electronic module B was damaged as a result of the accident (Figure 9). A connector associated with electronic module A was disconnected (Figure 10). The locking tabs were intact.
The BEA investigations are conducted with the sole objective of improving aviation safety and are not intended to apportion blame or liabilities.
9/12 BEA2017-0409.en/June 2020
Figure 9: damage to electronic Figure 10: connector of electronic module B. module A found disconnected
On the ignition system, the partial connection (tab not locked) of one of the two electronic modules - found disconnected - was not damaged. The read-out of the flight data shows, moreover, that the electronic module was duly connected during the engine tests before take-off. According to the different statements made, the module was not disconnected during the intervention by the emergency services or when the wreckage was removed. Consequently, the connection was not locked before take-off. The tab had probably not been correctly locked during a maintenance inspection. The disconnection might have occurred on impact with the ground or in flight following strong vibrations. These may have been caused when the right carburetor failed. If this disconnection occurred in flight, it made the electronic module concerned inoperative. The operation of only one electronic module leads to the ignition of only one spark plug per cylinder, instead of the normal two. This malfunction leads to a decrease in engine power. It was not possible to check the functionality of the second module due to the extent of its damage.
2.7.3.3 Other observations A brown liquid was identified in the bottom of the crankcase. It was a mixture of oil and water. The presence of this brown liquid is not explained. The internal condition of the engine did not show signs of defective lubrication in service. The rest of the engine showed no signs of damage.
2.8 Maintenance In the regular maintenance programme taken from the aircraft manufacturer’s maintenance manual, it is specified that reference must be made to the engine manufacturer’s maintenance manual to carry out the list of inspection operations. According to the recommendations of the engine manufacturer, a complete inspection of the carburetors must be carried out every 200 hours. At this time, the carburetors are completely disassembled and inspected. During this act, the needle, circlip and O-ring are disassembled and checked. The O-rings are systematically replaced.
The BEA investigations are conducted with the sole objective of improving aviation safety and are not intended to apportion blame or liabilities.
10/12 BEA2017-0409.en/June 2020 (9)Continuing In the CAMO(9) maintenance programme, a complete inspection of the carburetors is Airworthiness carried out every 400 hours. This modification with respect to the engine manufacturer’s Management (10) Organisation. recommendations was approved by the FOCA which took into account the maintenance workshop’s vast experience concerning this type of carburetor when approving this change (10) Federal Office to the inspection interval. of Civil Aviation. The FOCA indicated that in principle, the maintenance instructions are manufacturer recommendations. In certain conditions it is possible to set these aside if justified by objective reasons or if an alternative can be shown. The maintenance programme describes the deviations with respect to the manufacturer’s specifications which are, as applicable approved by the FOCA. This authority specified that when approving the aircraft maintenance programme (AMP), it was determined that the aeroplane in question flew about 400 hours per year. This implied, given all the recommendations, an immobilization every six weeks. According to the manufacturer, the carburetors must be inspected every 200 hours or every 12 months. On the basis of 400 operating hours, the carburetors were still therefore subject to this inspection once a year. They added that the maintenance workshop specified that no damage due to aging or wear of the carburetors had ever been detected during previous inspections (twice a year) making the approval for an extension to 400 h understandable. They also pointed out that this was in line with EASA’s current policy for general aviation to be “simpler, lighter, better” and the minimum maintenance programmes generally permit some difference with the manufacturer’s very cautious recommendations. The aeroplane was operated nearly 400 hours a year, i.e. a complete inspection of the carburetors every year. The maintenance workshop had not reported any singularity during the complete inspection of the carburetors. These were carried out:
19 June 2014, at 408 operating hours; 10 June 2015, at 700 operating hours; 29 April 2016, at 1,004 operating hours. The last complete overhaul of the carburetors was carried out on 29 April 2016 during the aeroplane’s 1,000 h inspection; at this time, the aircraft had logged 1,004 hours. Following this, there were eight reports of power losses in flight and/or engine vibrations. These reports gave rise to maintenance actions on the carburetors. None of these actions corresponded to a complete inspection of the carburetors. The float of the left carburetor was replaced on 23 March 2017, the aeroplane had logged 1,335 flight hours. The last report, dated 22 April 2017, indicated a loss of 200 rpm in cruise. The float of the right carburetor was replaced on 22 April 2017, the aeroplane had logged 1,367 flight hours, i.e. 126 flight hours before the accident. During the accident flight, it had logged 1,493 hours. The study of the different maintenance documents found that the aircraft 100-hour and 50-hour inspections had been carried out and complied with in accordance with the recommendations of the CAMO maintenance programme approved by the FOCA. The details of all the actions carried out concerning the engine maintenance were not all recorded in the main follow-up file. Some of these were archived by the maintenance workshop. As the traceability of these actions was not complete, the investigation was not able to check in detail all the maintenance actions carried out on the aeroplane.
The BEA investigations are conducted with the sole objective of improving aviation safety and are not intended to apportion blame or liabilities.
11/12 BEA2017-0409.en/June 2020 3 - LESSONS LEARNED AND CONCLUSION 3.1 Maintenance of carburetors
The aeroplane underwent the regular maintenance operations of the maintenance programme. The complete inspection of the carburetors was carried out every 400 hours instead of the 200 hours recommended by the manufacturer. At the time of the accident, the aeroplane had logged 489 hours since the last complete inspection of the carburetors. In addition, this last inspection was carried out over a year ago. Various engine related problems had been reported and treated since April 2015. The problems were varied: engine vibrations, power decreases, drop in rpm during take-off. The inspections which took place at 1,335 and 1,367 operating hours corresponded respectively to the replacement of the left and right float and probably an inspection of the bowl. The last complete inspection of the carburetors was carried out during the 1,004 flight hour inspection, i.e. one year and two months before the accident. During this, the carburetor needle was in all likelihood incorrectly reassembled. Since this inspection, eight reports of power loss and/or vibrations were behind maintenance actions on the carburetors. These “light” maintenance actions did not detect the needle assembly anomaly. If a complete inspection of the carburetors had been carried out 400 hours after the last complete inspection, i.e. at 1,400 operating hours, the problem would have probably been detected. At the time of the accident, the aeroplane had logged a flight time of 1,493 hours. If the manufacturer’s recommendations had been followed, the complete inspection of the carburetors every 200 hours would most probably have detected this problem a lot earlier. The needle of the right carburetor probably separated in flight, rendering the carburetor inoperative. The engine could not then operate in an optimal way as only the left carburetor remained operative, leading to a substantial power loss.
3.2 Conclusion Runway 05 is orientated towards lake Neuchâtel. During the initial climb from runway 05, there was a substantial power loss at low height. This power loss was probably due to the failure of the right carburetor. The non-compliance with the recommended interval between two complete inspections of the carburetors may have contributed to the singularity on the right carburetor not being detected. The disconnection of one of the electronic modules of the ignition system may have occurred in flight and thus may have played a part in the decrease in engine power. At this point, the aeroplane was at an altitude of 1,615 ft, i.e. a height of 186 ft. Its recorded airspeed was 54 kt, below the target speed of 60 kt recommended by the flight manual in the event of engine failure during take-off. The crew started a left turn. The presence of obstacles on the lake, for example water sports, or the concern about having to land on water may have influenced the crew in this choice. Holding the aeroplane nose-up after the decrease in power combined with a roll action probably led to the aeroplane entering a spin. Given the low height when the crew lost control, they were unable to regain control of the aeroplane. The strong vibrations caused by the loss of the right carburetor may have been a contributing factor to the loss of control.
The BEA investigations are conducted with the sole objective of improving aviation safety and are not intended to apportion blame or liabilities.
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