Flex temp is a technique used to produce cost savings through increased engine life and reduced overhaul and fuel costs for
airliner
An airliner is a type of aircraft for transporting passengers and air cargo. Such aircraft are most often operated by airlines. Although the definition of an airliner can vary from country to country, an airliner is typically defined as an ...
s by allowing them to
take-off at less than rated thrust.
For
Airbus
Airbus SE (; ; ; ) is a European Multinational corporation, multinational aerospace corporation. Airbus designs, manufactures and sells civil and military aerospace manufacturer, aerospace products worldwide and manufactures aircraft througho ...
and
Fokker
Fokker was a Dutch aircraft manufacturer named after its founder, Anthony Fokker. The company operated under several different names. It was founded in 1912 in Berlin, Germany, and became famous for its fighter aircraft in World War I. In 1919 ...
aircraft the technique is known as ''flex temp'' or just ''flex''. Other manufacturers use the terms ''Assumed temperature thrust reduction'', ''Reduced take-off thrust'' or ''Factored take-off thrust''.
Technique
The runway length required for an aircraft to take off depends on a number of things including aircraft weight, flap setting and environmental conditions. The particular take-off distance required may be less than the available runway length. In this case a lower thrust may be used. Lower thrust settings increase engine life and reduce maintenance costs.
The take-off thrust available from a civil engine is a constant value up to a particular ambient temperature. At this temperature the engine is now running at its turbine temperature limit which is displayed as a corresponding EGT limit. Since the turbine limit cannot be exceeded, any increase in ambient temperature results in less thrust. The flex temp procedure recognizes that an ambient temperature beyond the flat rating produces less thrust. If a lower-than-flat-rated thrust is calculated for a particular take-off that thrust can be specified by where it coincides with the EGT limit. This false ambient temperature is the flex temp.
The flex temp is entered into the
flight management system
A flight management system (FMS) is a fundamental component of a modern airliner's avionics. An FMS is a specialized computer system that automates a wide variety of in-flight tasks, reducing the workload on the flight crew to the point that mode ...
(FMS) — effectively telling the computer to assume the specified air temperature instead of the actual temperature. When flex (FLX) thrust is selected during take-off, the engine control produces that thrust. If necessary, the throttles may be advanced to the
take off/go around (TOGA) detent which requests rated thrust.
Problems
A number of aircraft incidents and accidents have occurred when the flex temp was incorrectly calculated or entered — for example, those involving
Emirates Flight 407
Emirates Flight 407 was a scheduled international passenger flight operated by Emirates from Auckland to Dubai with a stopover in Melbourne, operated by an Airbus A340-500 aircraft. On 20 March 2009, the flight failed to take off properly at M ...
, US Airways flight 1702 and
Thomas Cook Airlines
Thomas Cook Airlines Limited was a British charter and scheduled airline headquartered in Manchester, England. It was founded in 2007 from the merger of Thomas Cook Group and MyTravel Group, and was part of the Thomas Cook Group Airlines. It ...
G-OJMC.
[AAIB Bulletin: 11/2009]
"AAIB Bulletin: 11/2009"
UK Air Accidents Investigation Branch, 2009. Retrieved on 2009-12-20. Modern procedures are designed to minimize that possibility.
See also
*
Laker Airways, introduction of reduced thrust take-off technique
References
Avionics