Pilot Debrief

CESSNA TU206 near Deadhorse, AK — 2014-09-22

Final reportANC14LA085
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Date
2014-09-22
Location
Deadhorse, AK, USA
Airport
AK78
Aircraft
CESSNA TU206
Registration
N206J
Category
Airplane
Highest injury
None
Fatalities
0
Phase of flight
Climb

Probable cause

The application of insufficient torque to the engine cylinder through bolts during the replacement of the No. 1 cylinder, which resulted in the displacement of the No. 2 bearing, oil starvation, and a catastrophic engine failure.

NTSB narrative

The commercial pilot was conducting an on-demand air taxi commuter flight. The pilot reported that, during cruise flight, the engine began vibrating violently and lost power and that the throttle and propeller controls were unresponsive. The cockpit subsequently filled with smoke. The pilot conducted a forced landing to the nearest and driest tundra patch, during which the airplane nosed over. Examination of the engine revealed a large hole on the top left side of the crankcase near the No. 2 cylinder. The No. 2 connecting rod had separated from the crankshaft connecting rod journal. The No. 2 main bearing support mating surfaces exhibited fretting damage. The No. 2 main bearing had shed material from its forward side and had shifted. Measurements of the breakaway torque on the cylinder through bolts indicated that the torque on the Nos. 2 and 3 cylinder through bolts was below the engine manufacturer's specification. It is likely that the insufficient torque on the Nos. 2 and 3 cylinder through bolts resulted in the fretting damage and the No. 2 main bearing shifting and interrupted the oil flow to the No. 2 connecting rod bearing. The interruption of oil flow resulted in the bearing becoming starved of oil and overheating and the subsequent separation of the connecting rod from the crankshaft. A review of maintenance records revealed that the No. 1 cylinder was replaced about 403 flight hours before the accident, which would have required the removal and installation of hardware on the Nos. 1, 2, and 3 cylinder through bolts. It is likely that insufficient torque was applied to the through bolts during the replacement of the No. 1 cylinder.

Analysis

Primary failure mode
Engine power loss
First missed decision gate
Pilot could have performed an emergency landing sooner after engine issues began.

NTSB coding

Evidence available

  • Photos
  • 8 docket documents
View NTSB final reportView NTSB docket

Docket documents8

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