ASN Wikibase Occurrence # 314520
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| Date: | Thursday 17 March 2011 |
| Time: | 15:40 LT |
| Type: |  Bombardier DHC-8-402Q Dash 8 |
| Owner/operator: | Colgan Air |
| Registration: | N339NG |
| MSN: | 4339 |
| Year of manufacture: | 2010 |
| Engine model: | P&W Canada PW150A |
| Fatalities: | Fatalities: 0 / Occupants: 40 |
| Aircraft damage: | Minor |
| Category: | Serious incident |
| Location: | Pittsburgh, Pennsylvania -
 United States of America
|
| Phase: | En route |
| Nature: | Passenger - Scheduled |
| Departure airport: | Cleveland-Hopkins International Airport, OH (CLE/KCLE) |
| Bloomington-Normal Airport, IL (BMI/KBMI) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
A left engine aft thrust rotor bearing incipient spalling condition progressed to failure during cruise flight. The loss of rotor thrust support caused the rotor to displace aft and contact adjacent stationary structures, including structures in the No. 2 bearing area. The resulting machining-type contact damage generated metal debris that contaminated the engine oil. Metal particles in the oil scavenged from the No. 2/2.5 bearing oil cavity damaged the engine oil pump and arrested its rotation, which caused torsional separation of the oil pump driveshaft, cutting off oil supply to the engine. The left engine oil pressure master warning activated. The flight crew did not shut down the engine. The engine operated 84 seconds without oil flow, until combustor and turbine component fire damage disrupted combustor flame stability and the engine flamed out. The continued operation without oil flow elevated engine operating temperatures, and the No. 5 engine bearing cavity temperature increased beyond the material properties of the No. 5 bearing seal runner. The seal runner expanded radially and caused a hard rub against the (titanium-alloy) No. 5 bearing flexible support. The local temperature at the contact point rapidly reach its ignition temperature. The resulting titanium fire consumed the No. 5 bearing flexible support and progressed to adjacent thin-walled titanium components, including the diffuser diaphragm. Molten titanium droplets falling onto diffuser exit ducts located directly beneath the No. 5 bearing area melted through three of the exit ducts and penetrated the gas generator case. The titanium fire self-extinguished when the conditions required for sustained titanium combustion were altered by the flameout and the case burn-through. The lack of circumferential titanium droplet distribution, the undamaged condition of the diffuser ring bore internal surfaces, and the gravity-driven nature of the case penetration indicate that the titanium fire originated external to the diffuser/engine gas path. The cockpit engine fire warning remained active when no fire was present because one of the nacelle fire/overheat detector elements was unable to reset due to a permanently deformed switch diaphragm.
Probable Cause: the flight crew's delay in shutting down the left engine following an engine oil pressure master warning, which led to a hard rub inside the engine that served as an ignition point for a titanium fire. Contributing to the event was a PW150 No. 5 seal design vulnerability to titanium ignition that can occur with continued engine operation following an engine oil pressure loss event.
Accident investigation:
 |
|
Sources:
NTSB ENG11IA021
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 02-Jun-2023 17:59 | ASN Update Bot | Added |
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