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A flat rated turbofan engine has a constant maximum rated thrust level:
  • A
    up to a specific OAT.
  • B
    above a specific OAT.
  • C
    above a specific pressure altitude.
  • D
    up to a specific pressure altitude.
When the outside temperature is quite low, the denser air will induce an increase in the air mass flow for a given engine speed, and this will ultimately increase the thrust. Consequently, the denser air will allow the engine to produce the required take-off thrust before the limiting temperature has been reached. The limiting temperature is linked to the maximum available pressure ratio across the compressor and the maximum operating temperature of the turbine. A flat-rated jet engine is designed to provide constant maximum take-off thrust up to a certain ambient temperature (OAT). Therefore, on a very cold day, the engine will be able to deliver more thrust than its components can actually safely take. A flat rated gas turbine engine will be temperature limited if the OAT is higher than the flat rated temperature.

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