Bombardier DHC 8 402 N339NG

Summary

On 17 March 2011 at about 16:40 local time, a Bombardier DHC 8 402 registered N339NG, operated by Colgan Air, Inc., was involved in an incident near Pittsburgh, Pennsylvania, United States. 40 people were on board and nobody was injured. The aircraft was slightly damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

17 March 2011 at 16:40

Classification

Incident

Location

Pittsburgh, Pennsylvania, United States

Coordinates

40.4317, -80.0344

Aircraft

Bombardier DHC 8 402

Registration

N339NG

Category

Airplane

Year built

2010

Engines

2

Operator

Colgan Air, Inc.

Operating rule

Part 121: Air Carrier

Phase of flight

Not recorded

Route

Cleveland → Baltimore

Aircraft damage

Minor

Weather

Unk

Light

Day

NTSB number

ENG11IA021

Nobody was injured.

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.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

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.

Quoted verbatim from the NTSB record.