Commercial Fixed Wing
Maintenance Airframe; Maintenance Powerplant
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
General Maintenance Action
Aircraft; Procedure
I was tasked a Periodic Service Check with a removal and replacement of Fuel Control Unit of the APU on [the] aircraft. After completion of PS Check; I removed and replaced APU Fuel Control Unit referring [to] AMM. While performing Operation and Leak Check; I observed flames emitting from APU exhaust. I called to cockpit to notify of fire; then proceeded to extinguish fire and call to notify fire department and Lead. Subsequent to fire being extinguished; an inspection was performed on APU compartment and APU exhaust with no damage noted.
Air Carrier Maintenance Technician reported that while performing an operational check on the APU; flames started coming out of the exhaust.