Accessory gearbox input shaft coupling not engaged.
Accessory gear drives, bearings, or compressor rear hub splines are defective.
Engine fails to light up.
Improper engine starting procedure.
(1) No power to ignition exciter.
(2) Defective wiring or components.
(1) Debris or ice in fuel system.
(2) Air lock in fuel control unit.
(3) Engine driven primary high pressure pump failure.
(4) Flow divider and dump valve system failure.
Engine fails or is slow to accelerate to idle N1 speed.
Leaks or restrictions on fuel control unit pneumatic system.
Leaks in pneumatic line of propeller governor.
Fuel control unit contaminated with water or ice, or corroded.
Flow divider and dump valve malfunction.
Hot start or delayed light up.
Improper starting procedure.
Insufficient power from battery or ground power unit.
Poor connections on power input lines or starter-generator.
Low power to ignition exciter.