APU FIRE ON GND AFTER APU SHUTDOWN AND FLC DEPARTED ACFT.

Narrative

APPROX 5 MINS PRIOR TO LNDG; WE UNSUCCESSFULLY ATTEMPTED TO START APU. WE ASSUMED WE HAD A SWITCH LOGIC MALFUNCTION (WHICH HAPPENS FROM TIME-TO-TIME). AFTER LNDG; APU STARTED NORMALLY. ACFT WAS COMPLETELY SECURED AND FO COMPLETED POSTFLT (THUMBS UP). WE DEPARTED FOR HOTEL. WHILE AWAITING TRANSPORTATION; WE WERE PAGED BY OUR COMPANY AND INFORMED THAT RAMP AGENT SAW GLOW OF FLAMES FROM APU EXHAUST. FIRE DEPT WAS CALLED. BY THE TIME THEY ARRIVED THE FIRE HAD NEARLY BURNED ITSELF OUT. NO AGENT WAS DISPERSED. CFR PREDICTED THAT RESIDUAL FUEL HAD ACCUMULATED IN APU EXHAUST. NO DAMAGE WAS NOTED AS A RESULT (CONFINED TO EXHAUST STACK). FLT ATTENDANT LATER RPTED SMELLING FUMES DURING TAXI. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR ADVISED THAT NORMAL PROC IS TO START THE APU AFTER LNDG IF IT HAD NOT BEEN STARTED IN THE AIR. THE APU STARTED ON THE GND AND OPERATED AFTER THE ENGS WERE SHUT DOWN. PART OF THE PROC FOR SECURING THE ACFT FOR THE NIGHT IS TO TURN OFF THE APU. RPTR INDICATES THAT THIS WAS ACCOMPLISHED; AND THAT THE FLC WAS UNAWARE THAT A FIRE HAD STARTED UNTIL THEY WERE PAGED WHILE AWAITING TRANSPORTATION. THE FIRE DEPT ADVISED HIM THAT IT WAS PROBABLY SOME RESIDUAL FUEL THAT HAD IGNITED AND WOULD BURN ITSELF OUT; WHICH IT DID.