Office of Aviation Safety
ICAO Workshop Engines and Props June 3, 2013
Paul Cox NTSB Eastern Regional Office Ashburn, Virginia Engine Investigation Objectives
• Did the engine contribute to the accident or was it in some way a factor?
• No? • Gather information for future reference.
• Yes? • What was its relationship to the accident?
Engine Relationship to Accident
• Direct Cause • Causes aircraft to become uncontrollable • (For example, un-commanded thrust reverser deployment, or loss of engine power over unsuitable terrain/at night?) • Related Cause • Engine failure and pilot fails to maintain control • Indirect Cause • Distraction to pilot – for example, pilot fixation to engine parameter such as loss of oil pressure
Engine Relationship Questions
• Was it operating?
• Or- Was it capable of operation?
• If the engine(s) had an influence in the accident can/how do we correct the problem?
Introduction to Aircraft Turbine Engines
• Turbine engines are reliable • GE CF6-80C2 30,000 hours • RR RB211-535 40,531 hours
• But they are not perfect Turbine engine manufacturers
• CFM • General Electric • Honeywell • Pratt & Whitney • International Aero Engine • Pratt & Whitney Canada • Turbomeca • Rolls Royce/Allison • Snecma • Williams • Honda - GE • Walter - GE Types of turbine engines
All of the air entering the inlet goes through the engine.
Generally found on older, smaller corporate jets like the HS-125 and Lear Jets. Turbofan On turbofan engines, only a percentage of air entering inlet goes through the core of the engine. Turbofan (small)
TFE731 engine Lear Jet 35A Turbofan (medium)
CFM56 Used on: 737-300 and later, A320/319/A340 Turbofan (large)
Used on: A300, 747, 767, DC10, MD11 Turbofan (very large)
Rolls Royce Trent Used on: A330,340, 380, B777, 787 Turboprop
Turbine drives a propeller through a gearbox. All of the air entering the inlet goes through the engine.
MU-2 King Air
Used on corporate and commuter airplanes like King Airs, MU-2s, EMB-120s and SAAB 340s. Turboshaft
Typically used on helicopters. Similar to a turboprop with a free turbine that drives a shaft that drives the rotor blades. All the air entering the inlet goes through the engine. Turboshaft
Rolls-Royce Allison 250 Bell Jet Ranger Engine inlet • Inlet directs air into front of engine • Can vary in size and shape depending upon design and type of engine Compressor
• Compresses air entering engine, air is forced into a smaller area.
• Two types • Centrifugal flow • Axial flow
Centrifugal flow compressor
Axial flow compressor Compressor Rotors
• Multiple rotors – 1, 2, or 3
• Varying rotor directions • Clockwise – GE, P&W • Counterclockwise - RR • Both – PWC PW100
Individual combustion chamber in each tube.
Rolls Royce Nene
Rolls Royce Dart Can-annular combustors
Ring of combustion chambers within a common annulus.
Used on JT8D which is installed on 727 and DC-9 series. Annular combustors
A single ring-shaped piece where the fuel-air mixture is burned.
Nozzle Turbine blades
Compressor blades have “dove tails.”
Turbine blades have “fir trees.” Electronic engine controls
• EECs, DEECs, and FADECs
• Non-volatile memory (NVM) can be down loaded to show any faults and what engine was doing at impact. Electronic Engine Controls Engine Electronic Controls Thrust reversers • Deflect exhaust gases and/or fan flow forward to slow airplane
• Bucket or cascade type reversers Bucket type thrust reversers Cascade type thrust reversers Engine operation
Now that we have put together all of the pieces of a turbine engine, what happens when it runs? Air enters inlet
INLET Some air goes down the fan duct
Fan & compressors Some air goes through the compressors.
Amount of air through fan v. core is the bypass ratio.
Fan & compressors Fuel is added. The fuel/air mixture is burned in the combustor.
Combustor Exhaust gases go through turbines
Turbine Fan air and exhaust gas exit engine producing thrust
THRUST Engine cycle definition • Engine start • Engine acceleration to takeoff power • Engine power reduction to idle • Engine shutdown • Every time the engine completes one of these cycles, life limited parts will be debited one cycle. Engine Operation Stall vs. Surge
• What is meant by the term “surge” as applied to turbine engines?
• Is a “stall” the same as a “surge”? Stall vs. Surge
• The terms, "compressor stall" and "engine surge" are often used interchangeably.
• A compressor stall typically contains a rotating stall cell that reduces compressor pumping ability and performance.
• A stall-induced engine surge usually manifests as an explosive compressor flow reversal that occurs at higher engine power, and can be accompanied by visible flames from the tailpipe and inlet.
• Recoverable engine surges occur during a momentary disruption of airflow which do not require operator corrective action. Non-recoverable engine surges require operator corrective action, which can include retarding the thrust lever, increasing engine bleed, or engine shutdown. These surges will frequently recover if the thrust lever is immediately and rapidly retarded to idle. Compressor surges
• Typified by loud bangs and flames from inlet and tailpipe
• Caused by airflow disruption in compressor • Broken compressor or turbine blades • Foreign object ingestion • Engine deterioration • Extreme pitch or yaw movements • Throttle movements Compressor surge Piston Engines
• Intake • Compression • Power • Exhaust
• Piston Engine Operation – Multiple videos on You Tube
• Opposed (O) – Not fuel injected vs. fuel Injected (IO)
• Induction (Impact) Icing – At air Intake/Air Filter – Alternate Air Source • Can be automatic and/or Pull-and-Release T-handle
• Carburetor Icing
Carburetor Icing Prob Charts
• Good starting point for determining if engine under power
– Blade damage
– Blade position in the hub.
– Hub rotational damage
Warning!! Highly loaded springs in the hub!!!! Rotational Hub Damage
Evidence of Power Nicks, Gouges, Chordwise Scratches Evidence of Power - Composite
Power-On “S” (Torsional) Bending One Blade? Other Blade? Engine Power? When to Document Accident Engines?
• At the scene?
• At local hangar?
• At a local shop?
• At manufacturer? Accident Engine Documentation
• How far do you go?
– What does the propeller look like? – What are the needs of the investigation? – What is the general condition of the engine? – What assets (human/tools) do you have? – What follow-on options do you have? – Can you run the engine?
• When? – Not all accidents require it (example: CFIT) – Evidence is not clear or need more in-depth examination of internal parts
• Where? – Local shop with/without manufacturer participation – At manufacturer
• How? – Coordinate through AccRep for U.S. examination Shipping the engines
Ship the engines in separate sealed containers Propellers go too
Make sure the box will fit on the truck • BREAK
Turbine Accident Engine Examples
• Although provided here, you will typically have help.
Uncontained engine failure
An uncontained engine failure occurs when an internal part of the engine fails and is ejected, or results in other parts being ejected, through the cowling. Engine fires (undercowl) Engine fires (Tailpipe) • Tailpipe fires are generally not a safety of flight issue Foreign Object Ingestion • Two types: • Soft body impact damage: large radius of curvature, typically to a fan blade (birds, tire rubber, plastic, etc.)
• Hard body impact damage: serrated/deep cuts/tears to airfoil leading and trailing edges (metal, concrete, rocks, etc.) Foreign object impact damage
Hard body Impact damage Soft body impact damage Evidence of Engine Operation on Ground
Swath of grass bent over Wilted, scorched grass backwards opposite the just before impact mark direction of travel of the of engine airplane Fires Was the fire damage pre- or post- impact?
Post impact Fires - Ground fire
Soot trail rises vertically. Fires – In-flight
Soot trail back from origin of the fire Case ruptures
Case ruptures will be “petal’d” back in both directions. Thrust reversers
Grass in door
Open Dirt on inside, impact marks on forward edge Internal Blade Examination • Rotational damage: • Bending in direction opposite rotation • All blades bent in generally same manner
• Static impact damage: • Blades Crushed • Only a segment is affected • Some bent in direction of rotation Reverse bending
As rotor turns, case crushes down on blades, bending them away from rotation. Fan blade damage
Broken fan blades Fan blade damage
Damaged fan blades can vary from being broken and short to almost full length. Compressor blades are bent opposite direction of rotation. Foreign material
Nicks and dents on leading edges indicative of engine having ingested some foreign material. Foreign material
Wood chips pressed against underside of the mid-span shrouds. Airplane flew through trees prior to impact. Foreign material
Soft body impact damage Static impact damage
One or two impact marks on entire rotor may indicate engine was not operating at impact Static impact damage
On engines that separate before impact, typical to see sector of broken blades with arc of full length blades. Indicative the rotor had stopped before impact. Static impact damage
Imprints of blade tips on rub strips indicative that rotor stopped before impact. Tailpipe
Metal spray on turbine airfoils indicates that engine was breaking up while it was operating. Must look elsewhere to determine if it was pre or post impact . Bird Strike •
On turbojet, turboprop, and turboshaft engines; all bird remains will be contained within engine. Bird Strike
On turbofan engines, most bird remains will be centrifuged out into the fan duct. Bird Strike
CFM56 bird strike Bird strike • Bird remains, invisible to naked eye, can be seen under ultraviolet light
Helicopters • Location of engine and low impact speeds protect engine from damage that typically is used to determine if engine was running.
• Must check for evidence on drive train, but that indicates drive train rotation, but that is not assurance of engine producing power. Typical Piston Engine Documentation
• Police/witness reports (sputtering) • Exhaust system for malleable bending • Control positions • Type of engine/serial number • Obvious holes/cracks
• Rotate engine by hand – Crankshaft continuity – Listen for binding/strange noises/magneto impulse coupling – Cover spark plug holes and feel for compression (thumb check) Typical Piston Engine Documentation
Remove and check spark plugs
http://www.championaerospace.com/assets/AV6-R-Nov2004.pdf Typical Piston Engine Documentation
• Fuel supply systems – Sources (external/internal) – Fuel filter – Lines – Distribution (flow divider/spider/carburetor)
• Oil/lubrication – check/open oil filter • Drive accessories – Binding – Interior/vanes of the vacuum pump • Ignition systems
• Any Questions?