FLEX TEMPERATURE

Flex Temperature is a technique used to reduce noise and engine wear by performing take-off at less than full power or thrust.

The crew calculates a lower-power engine setting where take-off will use a larger portion of the runway which will reduce noise, engine wear, and maintenance costs and enters it into the flight management system(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 controller produces maximum thrust for the assumed (flex) temperature.

This technique is based on air temperature, rather than percentage of engine power, because it is easy for the crew to look up or calculate the highest air temperature at which any particular take-off can be performed. That temperature is the highest flex temp that can be used.

Jet engines produce reduced thrust as the ambient air temperature increases.

The flex temperature is the highest air temperature at which the engines would produce the required thrust.