Pilot Debrief

CESSNA 208B near Alpine, TX — 2017-07-03

Final reportCEN17LA254
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Date
2017-07-03
Location
Alpine, TX, USA
Airport
E38
Aircraft
CESSNA 208B
Registration
N9714B
Category
Airplane
Highest injury
Minor
Fatalities
0
Phase of flight
Initial climb

Probable cause

Fracture of a compressor turbine (CT) blade due to operational overtemperatures and the failure of a maintenance technician to detect an existing crack in the CT blade during the last engine inspection.

NTSB narrative

While on climbout on a cargo flight, the pilot heard a loud bang, followed by a squealing noise; the engine immediately lost power. The pilot accomplished a forced landing to a field, during which both wings were damaged after contacting power poles. Examination of the engine revealed the compressor turbine (CT) blades had fractured. Material analysis of the CT blades confirmed operational overtemperature conditions had occurred during previous flights, and significant creep in the microstructure of the blades indicated an imminent cracking probability in all the CT blades. During the last borescope inspection about 3 months before the accident, a crack in a CT blade that could be seen in a video recording of the inspection was not observed by the technician who conducted the inspection. It is likely that this CT blade failed due to creep and the undetected crack. The engine's compressor turbine vane ring had features different from an original equipment manufacturer part, including cooling air ducts that were a different size; however, the investigation was not able to determine if cooling air performance was compromised. The CT vane axial positioning, which was staggered, likely increased vibrational loads on the CT blades; however, the investigation was not able to determine if this contributed to the CT blade longevity and crack initiation.

Analysis

Primary failure mode
Engine power loss
First missed decision gate
Inspection of CT blades should have detected the crack before the flight.

NTSB coding

Evidence available

  • 3 docket documents
View NTSB final reportView NTSB docket

Docket documents3

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