Starting and ignition - RELIGHTING

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RELIGHTING

Fig. 11-14 A typical flight relight envelope.

28. The jet engine requires facilities for relighting should the flame in the combustion system be extin- guished during flight. However, the ability of the engine to relight will vary according to the altitude and forward
speed of the aircraft. A typical relight envelope, showing the flight conditions under which an engine will obtain a satisfactory relight, is shown in fig. 11-14. Within the limits of the envelope, the airflow through the engine will rotate the compressor at a speed satisfactory for relighting; all that is required therefore, provided that a fuel supply is available, is the operation of the ignition system. This is provided for by a separate switch that operates only the ignition system.