Serious incident Boeing 727-251 N295US, Sunday 20 January 1991

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Date:	Sunday 20 January 1991
Time:	21:45 LT
Type:	Boeing 727-251
Owner/operator:	Northwest Airlines
Registration:	N295US
MSN:	21506/1392
Year of manufacture:	1978
Engine model:	P&W JT8D-15
Fatalities:	Fatalities: 0 / Occupants: 44
Other fatalities:	0
Aircraft damage:	Minor
Category:	Serious incident
Location:	St. Paul, MN - United States of America
Phase:	Taxi
Nature:	Unknown
Departure airport:
Destination airport:	Philadelphia, PA (PHL
Investigating agency:	NTSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
THE FLIGHT CREW WAS INFORMED BY THE TOWER OF A FIRE ON THE RIGHT SIDE OF THE AIRPLANE WHILE TAXIING FOR TAKEOFF. THE FIRE PRECEEDED BY UTILIZING THE AUXILARY POWER UNIT (APU) FOR A MAIN ENGINE START. THE MAIN ENGINE START WAS ABORTED WHEN THE APU FAILED TO DELIVER SUFFICIENT BLEED AIR PRESSURE. A POST INCIDENT INSPECTION OF THE APU DISCLOSED A LIBERATED TURBINE EXDUCER BLADE WHICH CAUSED AN IMBALANCE OF THE TURBINE WHEEL, ALLOWING SMOPKE AND FLAMES TO ESCAPE FROM THE APU EXHAUST ATOP THE RIGHT WING ROOT. THERE HAS BEEN 7 SERVICE DIFFICULTY REPORTS AND 4 ACCIDENTS/INCIDENTS ASSOCIATED WITH EXDUCER FAILURES IN THIS MODEL APU IN THE LAST FIVE YEARS.

Probable Cause: THE PARTIAL FAILURE OF THE AIRPLANE'S AUXILIARY POWER UNIT, AND THE INADEQUATE COMPONENT PRODUCED BY THE MANUFACTURER.

Accident investigation: