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Cases › ENG11IA021 · Part 121 airline

BOMBARDIER INC DHC 8 402Colgan Air, Inc.

Pittsburgh, PA, USA · 2011-03-17·N339NG

0
fatal
0
serious
No injury
highest injury
Minor
damage
Replay the flight data135,094 samples · 41 parameters12:00:00.0 – 12:49:59.9AnalyseThe analystOne timeline · precedents · ask the docket · what the record saysGenerateInvestigation briefFacts, cause, recorder extremes, sequence, sourcesSourceNTSB docket5 documents on data.ntsb.gov

What happened

NTSB summary, verbatim

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.

Photographs

46the aircraft, and what the investigators found
Wreckage and site documentation · 46 photographs from the docket

Photographs are NTSB docket attachments — works of the US government, in the public domain. Captions are the Board’s own.

Probable cause

the Board's determination
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.

Occurrence sequence

5 stepsNTSB coding · CICTT taxonomy
  1. 1 · Enroute-cruise
    Powerplant sys/comp malf/fail
    defining event
  2. 2 · Enroute-cruise
    Fire/smoke (non-impact)
  3. 3 · Enroute-cruise
    Loss of engine power (total)
  4. 4 · Enroute-cruise
    Engine shutdown
  5. 5 · Enroute-cruise
    Sys/Comp malf/fail (non-power)

Findings

2 causal · 4 contributing
  • CAUSE
    Personnel issues › Action/decision › Info processing/decision › Decision making/judgment — Flight crew
  • CAUSE
    Aircraft › Aircraft power plant › Engine (turbine/turboprop) › Compressor section — Design
  • FACTOR
    Aircraft › Aircraft power plant › Engine (turbine/turboprop) › Turbine section — Damaged/degraded
  • FACTOR
    Aircraft › Aircraft power plant › Engine (turbine/turboprop) › Oil system — Damaged/degraded
  • FACTOR
    Aircraft › Aircraft power plant › Engine (turbine/turboprop) › Oil system — Inoperative
  • FACTOR
    Aircraft › Aircraft systems › Fire protection system › Detection system — Design

Sequence of events

13 timed eventsfrom the FDR factual report · claude-sonnet-5
  1. 12:02:30 EDTTakeoffp.3
    Weight on wheels main gear transitioned from 'Grnd' to 'Air'
  2. 12:27:32 EDTCruise at 23,000 ftp.3
    Master warning transitioned from 'No Warning' to 'Warning'; engine 1 oil pressure transitioned from 'No Warn' to 'Warn' and remained 'Warn' for rest of flight
  3. 12:27:41 EDTCruisep.3
    Master warning transitioned back to 'No Warning'
  4. 12:28:58 EDTCruisep.3
    Engine 1 torque decreased to 58%, engine 2 torque remained 71%, engine 1 fuel flow decreased to 1,328 pph, engine 2 fuel flow remained 1,288 pph
  5. 12:29:00 EDTCruisep.3
    Engine 1 torque decreased to 41%, engine 1 fuel flow decreased to 856 pph
  6. 12:29:08 EDTCruisep.3
    Engine 1 torque decreased to 0%, engine 2 torque decreased slightly to 70%, engine 1 fuel flow increased to 1,312 pph, engine 2 fuel flow decreased slightly to 1,272 pph
  7. 12:29:10 EDTCruisep.3
    Master warning transitioned back to 'Warning'; CWP Check Fire Det transitioned from 'No Warning' to 'Warning' and remained 'Warning' for rest of flight
  8. 12:29:18 EDTCruisep.3
    Master caution transitioned from 'Off' to 'On'
  9. 12:29:27 EDTCruisep.3
    Engine 1 fuel flow decreased to 0 pph
  10. 12:29:52 EDTCruisep.3
    Master warning transitioned back to 'No Warning' and remained 'No Warning' for rest of flight
  11. 12:30:15 EDTCruise/Descentp.4
    Master caution transitioned back to 'Off' and remained 'Off' for rest of flight
  12. 12:30:53 EDTDescentp.4
    Aircraft began its descent from 23,000 feet (approximately 3 minutes 21 seconds from when the engine 1 oil pressure transitioned from 'No Warn' to 'Warn')
  13. 12:49:35 EDTLandingp.4
    Weight on wheels main gear transitioned from 'Air' to 'Grnd'

NTSB analysis

from the final report

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.