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 analysis
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.
Text from the NTSB. Open the NTSB docket for ANC14LA085 for the full record.
Event
- Date
- Sep 22, 2014
- Type
- Accident
- Place
- Deadhorse, Alaska
- Nearest airport
- Badami (AK78)
- Highest injury
- None
- Weather
- Visual (VMC)
- Light
- Day
Cessna TU206
- N-number
- N206J
- Category
- Airplane
- Year built
- 1967
- Damage
- Substantial
- Operating rule
- Part 135 (charter and commuter)
From the NTSB aviation accident database: N-registered aircraft, events since 2008, data through Oct 28, 2026. The file is published monthly, so the latest weeks are incomplete and recent records can change. The official source is the NTSB aviation investigation search. CheckAero is independent and not affiliated with the NTSB.