Terms U.K.
See Flat Rating
(Otherwise termed equivalent or indicated airspeed.) The speed of the aircraft relative to the air as indicated by a calibrated instrument on the aircraft. The true airspeed, which is normally greater, can be calculated from the calibrated airspeed knowing the air density.
Net thrust is the propulsive force exerted by an engine on the airframe. At a given power setting (EPR or N1 ) this falls with air density as altitude increases; corrected net thrust is the thrust at sea level.
For specific maximum component temperatures, the engine thrust falls as the ambient air temperature rises — and vice-versa. This means that there is a critical air temperature above which the rated thrust cannot be achieved. For most modern engines this is called the 'flat rated temperature' because, at lower air temperatures the thrust is automatically limited to the rated thrust to maximise service life. The thrust falls anyway at temperatures above the flat rated temperature — which is often called the break point or break temperature.
Magnitude of aircraft velocity vector (relative to aerodrome coordinate system)
The service life of an aircraft engine is very dependent upon the operating temperatures of its components. The greater the power or trust generated, the higher the temperatures and the shorter the life. To balance performance and life requirements flat rated engines are assigned thrust ratings for take-off, climb and cruise which define normal maximum power settings.
The pilot cannot select a particular engine thrust; rather s/he chooses an appropriate setting of this parameter which is displayed in the cockpit. It is usually either the engine pressure ratio (EPR) or low- pressure rotor (or fan) rotational speed (N1 ).