What was found
APU TAIL PIPE FIRE. SMOKE REPORTED BY OTHER AIRCRAFT. FIRE CRASH RESCUE INSPECTED AND FOLLOWED BACK TO RAMP. AFTER BLOCK IN AND CREW DEBRIEF INSPECTED AFT ENG AND APU COMPARTMENT. WITH NO SMOKE OR DAMAGED NOTED, BUT COULD SMELL A SMOKE ODOR. RESTARTED APU, DURING APU START, HAD AN EXHAUST PIPE FLAME. ABORTED START AND PULLED APU FIRE HANDLE. DID NOT DISCHARGE AGENT. INSPECTED APU AREA FOR FIRE DAMAGE, NO DAMAGE NOTED. RESET ALL PULLED C/B FOR APU RUN . STARTED APU 4 TIMES LAST 2 STARTS NO FLAMES RAN IAW JRH GOT A FLAME AT APU START 2 TIMES FLAME EXTINGUISHES IMMEDIATELY, NO EGT SPIKE NO ERRATIC FUEL FLOW, APU ISOLATION VALVE ON AIR FLOW OPS CHECKS NORMAL PACKS OPS CKS NORMAL EGT STAYS WITHIN LIMITS 394-398 C WITH ALL 3 PACKS RUNNING. NO HISTORY IN THE LAST 30 DAYS A/C OK FOR SERVICE IAW M/M 49-00-00-5.