What was found
ON APPROACH INTO BED THE APU START COMMANDED ON ABOUT A 4-5 MI FINAL AT ABOUT 1500FT AGL. AT 300-400FT AGL A RED APU FIRE CAS ILLUMINATED & AURAL WARNING WAS OVERHEARD. APU FIRE & FIRE EXT 2 SWITCHES PRESSED. APU FIRE CAS EXTINGUISHED & APU WAS OBSERVED WITH DECREASING RPM. A NORMAL LANDING & TAXI OCCURRED, NO OUTSIDE OBSERVERS REPORTED ANYTHING, NO EMERGENCY DECLARED. INFLIGHT APU FIRE QRC & QRH COMPLETED. FOUND EXIT/EXHAUST DUCT COLLAPSED. PERFORMED A GVI OF APU WITH NO FINDINGS APU LOOKS NORMAL R & R NR 2 FIRE BOTTLE. INSTALLED NEW SQUIBS IAW AMM 26-21-01, 26-21-05. PERFORMED OPS TEST OF ENG & APU FIRE EXTINGUISHING SYS IAW AMM 26•11-00. R & R MUFFLER ASSY IAW AMM 49·81-01 .RAN APU, NO FAULTS NOTED.