What was found
(CAN) DURING START OF NR 3 ENGINE, IT WAS OBSERVED THERE WAS NO EGT. START WAS ABORTED & OBSERVED ALL PARAMETERS. MAINT INSPECTED AREA & REQUESTED ANOTHER START. NR 3 ENGINE STARTED & OBSERVED RAPID EGT RISE & ENG START ABORTED. MAINT INFORMED FLT DECK THAT THERE WAS A NR 3 ENG TAIL FIRE. FLT CREW NOTIFIED ATC. AN AIR START UNIT WAS USED TO START A/C AS APU WAS INOP. FUEL HAD DRIPPED ONTO AIR HOSE & CAUGHT FIRE. ASU SHUTDOWN IMMEDIATELY BEFORE FLT CREW COULD CARRY OUT EMERGENCY PROCEDURES FOR ENG TAIL FIRE. BOTH ASU AIR HOSE & TAIL FIRE WAS EXTINGUISHED SUCCESSFULLY BY MAINT. NR 3 ENGINE IGNITOR ASSY REPLACED & CHECKED SERVICEABLE IAW MM 74-00 PAGES 601-608. NO FURTHER INCIDENT.