NTSB Identification: FTW97IA160.
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Scheduled 14 CFR operation of WESTERN PACIFIC
Incident occurred Wednesday, April 16, 1997 in COLORADO SPGS, CO
Probable Cause Approval Date: 04/24/1998
Aircraft: Boeing 737-300, registration: N962WP
Injuries: 125 Uninjured.

NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.

While on short final to land, at approximately 200 feet above ground level, the APU fire warning light illuminated. The crew performed the appropriate procedures and the fire warning light extinguished. After landing, the crew had the fire department visually inspect the aircraft and follow the aircraft to the gate where the passengers were off loaded in normal fashion. Examination and testing of the APU revealed that a fire had occurred in the APU exhaust as a result of oil entering the hot exhaust gas stream due to leakage around the aft turbine bearing seal. The seal evidenced scoring around its circumference and the seal surface was treated, in accordance with the maintenance manual, by Metco spray. Due to previous history of oil leakage around the seals treated with Metco Spray, in 1988, Allied Signal changed the treatment to Tungsten carbide which eliminated the leakage problem. However, due to some operators having difficulty in obtaining the Tungsten carbide coating, the Metco spray coating procedure was left in the overhaul manual.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

An oil leak around the APU aft bearing seal which resulted in a fire in the APU exhaust.

Full narrative available

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