Turbine engine failure
A turbine engine failure occurs when a turbine engine unexpectedly stops producing power due to a malfunction other than fuel exhaustion. It often applies for aircraft, but other turbine engines can fail, like ground-based turbines used in power plants or combined diesel and gas vessels and vehicles.
Turbine engines in use on today's turbine-powered aircraft are very reliable. Engines operate efficiently with regularly scheduled inspections and maintenance. These units can have lives ranging in the thousands of hours of operation. 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.
The Federal Aviation Administration (FAA) was quoted as stating turbine engines have a failure rate of one per 375,000 flight hours, compared to of one every 3,200 flight hours for aircraft piston engines. Due to "gross under-reporting" of general aviation piston engines in-flight shutdowns (IFSD), the FAA has no reliable data and assessed the rate "between 1 per 1,000 and 1 per 10,000 flight hours". Continental Motors reports the FAA states general aviation engines experience one failures or IFSD every 10,000 flight hours, and states its Centurion engines is one per 20.7 thousand flight hours, lowering to one per 164 thousand flight hours in 2013-2014.
The General Electric GE90 has an in-flight shutdown rate (IFSD) of one per million engine flight-hours. The Pratt & Whitney Canada PT6 is known for its reliability with an in-flight shutdown rate of one per 333 thousand hours from 1963 to 2016, lowering to one per 651 thousand hours over 12 months in 2016.
Following an engine shutdown, a precautionary landing is usually performed with airport fire and rescue equipment positioned near the runway. The prompt landing is a precaution against the risk that another engine will fail later in the flight or that the engine failure that has already occurred may have caused or been caused by other as-yet unknown damage or malfunction of aircraft systems (such as fire or damage to aircraft flight controls) that may pose a continuing risk to the flight. Once the airplane lands, fire department personnel assist with inspecting the airplane to ensure it is safe before it taxis to its parking position.
Turboprop-powered aircraft and turboshaft-powered helicopters are also powered by turbine engines and are subject to engine failures for many similar reasons as jet-powered aircraft. In the case of an engine failure in a helicopter, it is often possible for the pilot to enter autorotation, using the unpowered rotor to slow the aircraft's descent and provide a measure of control, usually allowing for a safe emergency landing even without engine power.
Shutdowns 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 in a jet powered aircraft 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 jet engine that can be caused by engine deterioration, a crosswind over the engine's inlet, ice accumulation around the engine inlet, ingestion of foreign material, or an internal component failure such as a broken blade. While this situation can be alarming, the engine may recover with no damage.
Other events that can happen with jet engines, 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.
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 or icing. Weather risks such as these can sometimes be countered through the usage of supplementary ignition or anti-icing systems.
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. 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
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.
Contained and uncontained failures
Engine failures may be described as either as "contained" or "uncontained".
- 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.
- An uncontained engine event occurs when an engine failure results in fragments of rotating engine parts penetrating and exiting through the engine case. Uncontained turbine engine disk failures within an aircraft engine present a direct hazard to an airplane and its passengers because high-energy disk fragments can penetrate the cabin or fuel tanks, damage flight control surfaces, or sever flammable fluid or hydraulic lines.
Engine cases are not designed to contain failed turbine disks. Instead, the risk of uncontained disk failure is mitigated by designating disks as safety-critical parts, defined as the parts of an engine whose failure is likely to present a direct hazard to the aircraft. Engine manufacturers are required by the FAA to perform blade off tests to ensure containment of shrapnel if blade separation occurs.
Notable uncontained engine failure accidents
- 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, resulting in one fatality.
- Two LOT Polish Airlines flights, both Ilyushin Il-62s, suffered catastrophic uncontained engine failures in the 1980s. The first was in 1980 on LOT Polish Airlines Flight 7 where flight controls were destroyed, killing all 87 on board. In 1987, on LOT Polish Airlines Flight 5055, the aircraft's inner left (#2) engine, damaged the outer left (#1) engine, setting both on fire and causing loss of flight controls, leading to an eventual crash, which killed all 183 people on board. In both cases, the turbine shaft in engine #2 disintegrated due to production defects in the engines' bearings, which were missing rollers.
- 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. Two people died.
- British Airtours Flight 28M: a Boeing 737 flying from Manchester to Corfu in 1985 suffered an uncontained engine failure and fire on takeoff. The takeoff was aborted and the plane turned onto a taxiway and began evacuating. Fifty-five passengers and crew were unable to escape and died of smoke inhalation. The accident led to major changes to improve the survivability of aircraft evacuations.
- 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 low as one in a billion. 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.
- Baikal Airlines Flight 130: a starter of engine No. 2 on a Tu-154 heading from Irkutsk to Domodedovo, Moscow in 1994, failed to stop after engine startup and continued to operate at over 40,000 rpm with open bleed valves from engines, which caused an uncontained failure of the starter. A detached turbine disk damaged fuel and oil supply lines (which caused fire) and hydraulic lines. The fire-extinguishing system failed to stop the fire, and the plane diverted back to Irkutsk. However, due to loss of hydraulic pressure the crew lost control of the plane, which subsequently crashed into a dairy farm killing all 124 on board and one on the ground.
- 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. Two died.
- Qantas Flight 32: an Airbus A380 flying from London Heathrow to Sydney (via Singapore) in 2010 had an uncontained failure in a Rolls-Royce Trent 900 engine. The failure was found to have been caused by a misaligned counter bore within a stub oil pipe leading to a fatigue fracture. This in turn led to an oil leakage followed by an oil fire in the engine. The fire led to the release of the Intermediate Pressure Turbine (IPT) disc. The airplane, however, landed safely. This led to the grounding of the entire Qantas A380 fleet.
- British Airways Flight 2276: a Boeing 777-200ER flying from Las Vegas to London in 2015 suffered an uncontained engine failure on its #1 GE90 engine during takeoff, resulting in a large fire on its port side. The aircraft successfully aborted takeoff and the plane was evacuated with no fatalities.
- Southwest Airlines Flight 3472: a Boeing 737-700 flying from New Orleans to Orlando in 2016 suffered an uncontained engine failure on its #1 engine during climb resulting in a puncture to left side of the fuselage causing a loss of cabin pressure and damage to the wing and empennage. The aircraft diverted to Pensacola International Airport, FL for a safe landing on runway 17 about 20 minutes later without further incident. There were no injuries.
- American Airlines Flight 383: a Boeing 767-300ER flying from Chicago to Miami in 2016 suffered an uncontained engine failure on its #2 engine during takeoff resulting in a large fire which destroyed the outer right wing. The aircraft aborted takeoff and was evacuated with 21 minor injuries, but no fatalities.
- Air France Flight 66: an Airbus A380, registration F-HPJE performing flight from Paris Charles de Gaulle (France) to Los Angeles, CA (USA), was en route at FL370 about 200 nautical miles (230 mi; 370 km) southeast of Nuuk (Greenland) when it suffered a catastrophic engine failure in 2017. The crew descended the aircraft to FL310 and diverted to Goose Bay, NL (Canada) for a safe landing about two hours later.
- Southwest Airlines Flight 1380: a Boeing 737-700 flying from New York to Dallas in 2018 suffered an uncontained engine failure on its #1 engine during climb resulting in a puncture to left side of the fuselage causing a loss of cabin pressure and damage to the wing and empennage. The aircraft diverted to Philadelphia International Airport, PA for a safe landing. There was one fatality.
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