A hung start is identified by abnormally slow acceleration after light-off and rpm stabilization below idle range. A hung start may be the result of fuel scheduling being either too rich or too lean. A lean hung start is associated with low fuel flow and proportionally low EGT. A rich hung start can be recognized by high fuel flow and rapid EGT rise that may develop into an over temperature condition. The starter air pressure, starting fuel flow, maximum rpm (N2) achieved and, maximum EGT should be recorded in the aircraft tech log to assist maintenance action.
Hung starts may be caused by:
- Inadequate starter air pressure, faulty start valve, or premature starter deactivation; - Compressor quality or foreign object damage (FOD); - Faulty pressurizing valve; - Incorrect variable starter vane (VSV) scheduling; - Turbine section damage.
Crew action in case of hung start
Automatic Start – while on Ground
If engine acceleration ceases and there has been no reduction in the acceleration fuel schedule, and there is no stall or over temperature indication, the crew must abort the start by placing the engine master switch to off and dry crank for 30 seconds remaining within the starter duty time limits. If engine acceleration ceases and there has been previous reduction in acceleration fuel schedule and there is no stall or over temperature indication, FADEC automatically increases the acceleration fuel schedule to accomplish acceleration to idle. No crew action required except to monitor starter duty time limits. If a rich hung start is encountered FADEC performs automatic sequence to keep the engine within the start limits. No crew action required except to monitor correct FADEC sequence.
ENG START FAULT ECAM shall not be cleared as the ENG MASTER ....OFF ECAM will not appear and starter limit may be exceeded.
Manual Start – Ground
A rich hung start must be aborted and the aborted start procedure followed. In flight the 30 second dry crank or wind milling time between start attempts is not required. For a lean condition hung start, increasing starter air pressure or wind milling N2 speed may be beneficial. If a hung start cannot be alleviated abort start.
Automatic Start – In Flight
A rich hung start must be aborted. The 30 seconds dry crank or wind milling time between start attempts is not required. For lean condition starts, increasing starter air pressure or wind milling N2 speed may be beneficial.
NOTE: When crew suspect that a hung start is the result of engine damage, no further start attempts shall be made and engineering guidance shall be sought.