Turbine engine failure

A turbine engine failure refers to an incident wherein a turbine engine in an aircraft unexpectedly stops producing power because of a part malfunction, in the absence of circumstances such as fuel exhaustion.

Nature of failures

Jet engines in use on today’s commercial airliners are quite reliable. It is common for engines to operate for tens of thousands of hours without difficulty before being removed from service for 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 safety of flight issue. Following an engine shutdown, a precautionary landing is 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 the gate.

Things that are not failures

Most in-flight shutdowns are benign 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 that can cause an odor or oily mist in the cabin. Despite these observations, such occurrences do not necessarily indicate an unsafe condition.

Contained versus uncontained failures

The engine of Delta Air Lines Flight 1288 after it experienced catastrophic uncontained turbine failure in 1996.

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.

Here are a number of examples of uncontained engine failures incidents or accidents:

• Qantas Flight 32: an A-380 flying from Singapore to Sydney in 2010 had an oil fire in a Rolls-Royce Trent 900 engine. No fatalities.
• Delta Air Lines Flight 1288: an MD-88 flying from Pensacola, Florida to Atlanta in 1996 had hub crack in a Pratt & Whitney JT8D-219 engine. 2 fatalities.
• United Airlines Flight 232: a 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 fatalities.
• National Airlines Flight 27: a DC-10 flying from Miami to San Francisco in 1973 had an overspeed failure of a General Electric CF6-6. 1 Fatality.

References

• "Jet Engine Problems" United States National Transportation Safety Board accessed 4 November 2010
• "Engine Failure: Guidance for Controllers" accessed 4 November 2010

This article is an adaptation of a publication of the United States National Transportation Safety Board which can be found here. As a work of the United States Federal Government, the source is in the public domain and may be adapted freely per USC Title 17; Chapter 1; §105 (see Wikipedia:Public Domain).