What was found
ENROUTE WITH APU RUNNING, SHUTDOWN APU AND APU DOOR OPEN CAUTION ILLUMINATED. FOLLOWED CH7 PROCEDURE AND STARTED THE APU AND DURING START HAD A MAST WARN ON APU FOR ABOUT 2-3 SECONDS INDICATING APU FIRE. START ABORTED MAST WARN WENT OUT AND HAD APU SOV CLSD GREEN MESSAGE WITH THE APU DOOR OPEN CAUTION AND APU DOOR STATUS INDICATING AMBER DASHES. THERE WERE NO OTHER INDICATIONS OF FIRE AND ALL OPS PROCEDURES NORMAL WITH THE FLIGHT. PERFORMED A VISUAL INSPECTION OF THE APU BAY AREA. NO DEFECTS NOTED. COMPLIED WITH FIM PROCEDURES IAW FOR APU FIRE WARNING IAW 26-22-00.