A "hot start" in any variant of a jet engine refers to the circumstance where the manufacturer defined limiting temperature for start has been exceeded. This temperature limit will be expressed as one of turbine inlet temperature (TIT), exhaust gas temperature (EGT) or interstage turbine temperature (ITT) as appropriate to the engine. The start temperature limit varies by manufacturer and engine type and can be less than, equal to or greater than the normal maximum operating temperature for the engine in question.
The most common reasons for a hot start include insufficient airflow through the compressor, incorrect fuel scheduling and slow engine acceleration. Contributing factors include insufficient bleed air from the auxiliary power unit (APU) or ground support unit (GSU) to properly accelerate the engine during the start and reverse airflow caused by a wind blowing from behind the aircraft.
If a potential hot start is identified by the pilot or by the Full Authority Digital Engine Control (FADEC) and the start is aborted before the limiting temperature is reached, a second start may be attempted. If the limiting temperature for start is exceeded, maintenance action is required.