What was found
ON TAKE-OFF ROLL, CREW GOT AN APU FIRE IND, BOTH BELL, ANNUNCIATION. WITH APU MASTER SWITCH ALREADY OFF, FIRED EXTINGUISHER, EXITED RUNWAY, STOPPED. WITH FIRE ANNUN STILL ILLUMINATED AN EVAC TOOK PLACE. CLEARED AC, BATTERY PWR WAS TURNED ON, FIRE ANNUNCIATION WAS GONE. NO IND THAT ACTUAL FIRE TOOK PLACE. AC WAS TOWED BACK TO HANGAR. AFTER THOROUGH INVESTIGATION, MAINT FOUND THAT APU FUEL BOOST PUMP MOTOR HAD OVERHEATED. WITH MOTOR COVER REMOVED, REAR BRG/BRUSH AREA WAS MILDLY CHARRED. EVIDENCE OF POSSIBLE FUEL MIGRATION INTO MOTOR. CHECKS OF ALL APPLICABLE COMPONENTS, AC WAS OPERATED, TEST-FLOWN WITH NO FURTHER PROBLEMS. ESTIMATED TIME FIRE WARNING TOOK PLACE AFTER APU WAS SHUTDOWN WAS ABOUT 4 MINUTES.