Fuel control unit

Gas turbine engines are primarily controlled by the amount of fuel supplied to the combustion chambers.

Many pre-production models of early turbojet engines featured just that, but it was soon found that this kind of control was difficult and dangerous in actual use.

Closing the valve too quickly while trying to reduce power output could cause a lean die-out, where the airflow through the engine blows the flame out of the combustion chamber and extinguishes it.

Adding fuel too quickly to increase power can damage the turbines due to excessive heat, or the sudden rise in combustion chamber pressure may cause a compressor stall.

The excess fuel may then be heated on the hot tailpipe and ignite, possibly causing damage to the aircraft.