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Uncontained engine failure

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Title: Uncontained engine failure  
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Uncontained engine failure

A turbine engine failure occurs when a turbine engine in an aircraft unexpectedly stops producing thrust due to a malfunction other than fuel exhaustion.

Turbine engines in use on today’s turbine-powered aircraft are extremely reliable. It is common for engines to operate for tens of thousands of hours without difficulty before being removed from service for a scheduled inspection. However, engine malfunctions or failures occasionally occur that require an engine to be shut down in flight. Since multi-engine airplanes are designed to fly with one engine inoperative and flight crews are trained to fly with one engine inoperative, the in-flight shutdown of an engine typically does not constitute a serious safety of flight issue. Following an engine shutdown, a precautionary landing is usually performed with airport fire and rescue equipment positioned near the runway. Once the airplane lands, fire department personnel assist with inspecting the airplane to ensure it is safe before it taxis to its parking position.

Shut downs that are not engine failures

Most in-flight shutdowns are harmless and likely to go unnoticed by passengers. For example, it may be prudent for the flight crew to shut down an engine and perform a precautionary landing in the event of a low oil pressure or high oil temperature warning in the cockpit. However, passengers may become quite alarmed by other engine events such as a compressor surge — a malfunction that is typified by loud bangs and even flames from the engine’s inlet and tailpipe. A compressor surge is a disruption of the airflow through a gas turbine engine that can be caused by engine deterioration, a crosswind over the engine’s inlet, ingestion of foreign material, or an internal component failure such as a broken blade. While this situation can be alarming, the condition is momentary and not dangerous.

Other events such as a fuel control fault can result in excess fuel in the engine’s combustor. This additional fuel can result in flames extending from the engine’s exhaust pipe. As alarming as this would appear, at no time is the engine itself actually on fire.

Also, the failure of certain components in the engine may result in a release of oil into bleed air that can cause an odor or oily mist in the cabin. This is known as a fume event. The dangers of fume events are the subject of debate in both aviation and medicine.[1]

Possible causes

Engine failures can be caused by mechanical problems in the engine itself, such as damage to portions of the turbine or oil leaks, as well as damage outside the engine such as fuel pump problems or fuel contamination. A turbine engine failure can also be caused by entirely external factors, such as volcanic ash, bird strikes or weather conditions like precipitation, icing or severe turbulence. Weather risks such as these can be countered through the usage of ignition or anti-icing.[2]

Failures during takeoff

A turbine-powered aircraft's takeoff procedure is designed around ensuring that an engine failure will not endanger the flight. This is done by planning the takeoff around three critical V speeds, V1, VR and V2. V1 is the critical engine failure recognition speed, the speed at which a takeoff can be continued with an engine failure, and the speed at which stopping distance is no longer guaranteed in the event of a rejected takeoff. VR is the speed at which the nose is lifted off the runway, a process known as rotation. V2 is the single-engine safety speed, the single engine climb speed.[3] The use of these speeds ensure that either sufficient thrust to continue the takeoff, or sufficient stopping distance to reject it will be available at all times.

Failure during Extended Operations

Main article: ETOPS

In order to allow twin-engined aircraft to fly longer routes that are over an hour from a suitable diversion airport, a set of rules known as ETOPS(Extended Twin-engine Operational Performance Standards) is used to ensure a twin turbine engine powered aircraft is able to safely arrive at a diversionary airport after an engine failure or shutdown, as well as to minimize the risk of a failure. ETOPS includes maintenance requirements, such as frequent and meticulously logged inspections and operation requirements such as flight crew training and ETOPS-specific procedures.[4]

Contained and uncontained failures


Two terms are helpful in describing the nature of engine failures. A “contained” engine failure is one in which components might separate inside the engine but either remain within the engine’s cases or exit the engine through the tail pipe. This is a design feature of all engines and generally should not pose an immediate flight risk. An “uncontained” engine failure can be more serious because pieces from the engine exit the engine at high speeds in other directions, posing potential danger to the aircraft structure and persons within the plane. In the United States, the National Transportation Safety Board will likely investigate any uncontained engine failure involving a transport category aircraft.

Notable Uncontained Engine Failure Incidents

  • Qantas Flight 32: an Airbus A380 flying from Singapore to Sydney in 2010 had an oil fire in a Rolls-Royce Trent 900 engine. There were no injuries or fatalities and the aircraft safely made it back to Singapore.
  • Delta Air Lines Flight 1288: a McDonnell Douglas MD-88 flying from Pensacola, Florida to Atlanta in 1996 had a cracked compressor rotor hub failure on one of its Pratt & Whitney JT8D-219 engines. 2 died.
  • United Airlines Flight 232: a McDonnell Douglas DC-10 flying from Denver to Chicago in 1989. The failure of the rear General Electric CF6-6 engine caused the loss of all hydraulics forcing the pilots to attempt a landing using differential thrust. 111 fatalities. Prior to the United 232 crash, the probability of a simultaneous failure of all three hydraulic systems was considered as high as a billion-to-one. However, the statistical models used to come up with this figure did not account for the fact that the number-two engine was mounted at the tail close to all the hydraulic lines, nor the possibility that an engine failure would release many fragments in many directions. Since then, more modern aircraft engine designs have focused on keeping shrapnel from penetrating the cowling or ductwork, and have increasingly utilized high-strength composite materials to achieve the required penetration resistance while keeping the weight low.
  • Cameroon Airlines Flight 786: a Boeing 737 flying between Douala and Garoua, Cameroon in 1984 had a failure of a Pratt & Whitney JT8D-15 engine. 2 people died.
  • Two LOT Polish Airlines flights, both Ilyushin Il-62s, suffered catastrophic uncontained engine failures in the 1980s. The first was in 1980 on LOT Flight 7, destroying the flight controls in a matter of seconds and killing all 87 on board. In 1987, a similar turbine failure happened on LOT Flight 5055. The aircraft's inner left (#2) engine, damaged the outer left (#1) engine, setting both on fire. Shrapnel from the explosion also penetrated the fuselage, causing a decompression. The crew tried unsuccessfully to return to the airport, with the aircraft ultimately losing control, breaking up, and crashing only moments short of an emergency landing. All 183 people on board were killed. In both cases, the turbine shaft in engine #2 disintegrated due to production defects in the engines' bearings, which were missing rollers.[5]
  • National Airlines Flight 27: a McDonnell Douglas DC-10 flying from Miami to San Francisco in 1973 had an overspeed failure of a General Electric CF6-6. One fatality resulted.

References

  • "Engine Failure: Guidance for Controllers" accessed 4 November 2010
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