Air carrier dhc-8-400 captain reports APU explosion while parked at the gate. No fire resulted and t...

Attributes
ACN	732029
Time
Date	200703
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	agl single value : 0
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Dash 8-400
Operating Under FAR Part	Part 121
Flight Phase	ground : parked
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : cfi
Experience	flight time last 90 days : 240 flight time total : 16000 flight time type : 3000
ASRS Report	732029
Person 2
Affiliation	company : air carrier
Function	other personnel
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	other other : 2
Resolutory Action	none taken : detected after the fact
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

Parked at the gate in ZZZ I attempted to start the APU. Approximately 7 seconds later after pressing the start select switch there was a bang and the aircraft rocked! At first I thought that the ground agents had struck the aircraft with a tug or belt loader. I looked up at the APU panel and noted a 'fail' message indicated. There was no fire indication or squib blown. At that point 3 or 4 ground agents ran forward and told us to get the passenger off the aircraft; that the APU had exploded! We executed a normal expeditious passenger evacuation of our 73 passenger and crew of 4. Crash fire rescue equipment arrived but there was no fire or injuries. It appears that excess fuel in the APU ignited; causing damage to the APU access doors; the rear firewall bulkhead; APU mounting and harness; APU ducting; external aircraft skin and the APU itself. Preliminary findings suggest that an improperly assembled drain plug was allowing excess fuel to collect and pool rather than drain.

Original NASA ASRS Text

Title: ACR DHC-8-400 CAPT RPTS APU EXPLOSION WHILE PARKED AT THE GATE. NO FIRE RESULTED AND THE ACFT WAS EVACUATED WITHOUT INCIDENT.

Narrative: PARKED AT THE GATE IN ZZZ I ATTEMPTED TO START THE APU. APPROX 7 SECONDS LATER AFTER PRESSING THE START SELECT SWITCH THERE WAS A BANG AND THE ACFT ROCKED! AT FIRST I THOUGHT THAT THE GND AGENTS HAD STRUCK THE ACFT WITH A TUG OR BELT LOADER. I LOOKED UP AT THE APU PANEL AND NOTED A 'FAIL' MESSAGE INDICATED. THERE WAS NO FIRE INDICATION OR SQUIB BLOWN. AT THAT POINT 3 OR 4 GND AGENTS RAN FORWARD AND TOLD US TO GET THE PAX OFF THE ACFT; THAT THE APU HAD EXPLODED! WE EXECUTED A NORMAL EXPEDITIOUS PAX EVACUATION OF OUR 73 PAX AND CREW OF 4. CFR ARRIVED BUT THERE WAS NO FIRE OR INJURIES. IT APPEARS THAT EXCESS FUEL IN THE APU IGNITED; CAUSING DAMAGE TO THE APU ACCESS DOORS; THE REAR FIREWALL BULKHEAD; APU MOUNTING AND HARNESS; APU DUCTING; EXTERNAL ACFT SKIN AND THE APU ITSELF. PRELIMINARY FINDINGS SUGGEST THAT AN IMPROPERLY ASSEMBLED DRAIN PLUG WAS ALLOWING EXCESS FUEL TO COLLECT AND POOL RATHER THAN DRAIN.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Air carrier dhc-8-400 captain reports APU explosion while parked at the gate. No fire resulted and the aircraft was evacuated without incident.