Flameout

In aviation a flameout refers to the run-down of a jet engine caused by the extinction of the flame in the combustion chamber. It can be caused by a number of factors, including fuel starvation, compressor stall, insufficient oxygen (at high altitudes), foreign object damage (such as caused by birds, hail or volcanic ash), severe inclement weather, mechanical failure and very cold ambient temperatures.[1][2]

Description

A flameout is most likely to occur when flying through certain weather conditions at a low power setting such as flight idle (e.g. during the descent). These conditions include flight through moderate to heavy turbulence, rain, hail or sleet. The potentially hazardous circumstances are highlighted in the flight manual with a requirement to select continuous ignition. Alternatively, the FADEC engine controller will select ignition automatically if it detects specific changes in engine parameters. It will also perform a relight if necessary. A manual re-light attempt is made by following the procedure in the Flight Operations Manual.[3]

Early jet engines, such as Junkers Jumo 004 used in early German jets, including the Messerschmitt Me 262, were at relatively high risk of flameout. Fast acceleration or inappropriate throttle settings could impoverish the fuel/air mixture causing a flameout. If this happened at low altitude, it would often lead to the total loss of the aircraft. However, jet engines were developed to be controlled with a governor, a centrifugal feedback valve for controlling the speed of the engine - sometimes referred to as FCU (Fuel Control Unit) or HMU (Hydro-Mechanical Unit) - allowing controlled fuel metering proportional to the engine's rotational speed. Current modern engines are engineered to a higher degree of technical quality controlled by digital electronic systems (FADEC) that constantly fine-tune their performance; thus such flameouts are not as common as they were in the early days of jet-powered aviation.

It is common practice for pilots to be taught and to practice flameout landings.[4]

Windmill restart

In-flight restarts are designated as either windmill or starter-assisted, depending where in the flight envelope the restart is attempted. The re-light envelope occupies the lower part of the flight envelope below about 30,000 ft (28,000 ft in the case of a Boeing 747, which experienced flameouts at 37,000 ft[5]). When an appropriate initial altitude and forward speed are available, the mass airflow through the compressor blades can maintain sufficient rotational velocity for enough time to permit restart. If the aircraft's operating conditions are not sufficient for a windmill start, the engine's starter motor must be operated to increase the turbine velocity to the minimum required speed.[6]

Notable incidents of flameout

Engine flameout due to inclement weather and volcanic activity

Engine flameout due to fuel starvation

Engine flameout due to mechanical problems

Other examples

References

  1. "''Turbo Jet Flame Out'' by Ask a Scientist". Newton.dep.anl.gov. Retrieved 2012-03-25.
  2. "''Flameout - Why the fire in a perfectly healthy jet engine can die.'' by Peter Garrison, Air & Space Magazine, September 01, 2006". Airspacemag.com. Retrieved 2012-03-25.
  3. "''Airplane Turbofan Engine Operation and Malfunctions'', FAA Manual". Webcache.googleusercontent.com. Retrieved 2012-03-25.
  4. Flightglobal archive flight International 10 July 1982 p59
  5. "Gas Turbine Performance" 2nd edition P.P.Walsh P. Fletcher ISBN 0-632-06434-X p484
  6. "AAIB Bulletin 12/2015" (PDF). Air Accidents Investigation Branch, Department for Transport. Retrieved 10/12/2015. Check date values in: |access-date= (help)
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