Mechanical & Engine Failure · NTSB ERA11FA078
CESSNA U206G — Leverett, MA
| Date | December 5, 2010 |
| Location | Leverett, MA |
| Aircraft | CESSNA U206G |
| Purpose of flight | Personal |
| Conditions | Day · Visual Meteorological Cond |
| Phase / occurrence | Emergency descent Off-field or emergency landing |
| Pilot age | 23 |
| Pilot total time | 390 hrs · Building experience |
| Time in type | 90 hrs |
| Fatalities | 2, 2 serious |
Probable cause
NTSB findings
- Aircraft-Aircraft power plant-Engine (reciprocating)-Recip eng cyl section-Incorrect service/maintenance - C
- Personnel issues-Action/decision-Action-Incorrect action performance-Maintenance personnel - C
- Environmental issues-Physical environment-Object/animal/substance-Wire-Contributed to outcome
What happened
The airplane was in cruise flight at 3,000 feet above ground level when the engine developed vibrations and, shortly after, lost total power. The pilot conducted a forced landing in an open field. The pilot cleared the trees adjacent to the field but did not see the electrical wires on the other side. The airplane’s main landing gear contacted the wires, and the airplane flipped and impacted the ground inverted. Examination of the engine revealed that several incorrect nuts for the cylinder hold-down studs were installed, and the breakaway torque values measured for the cylinder hold-down nuts were consistent with improper torque having been applied. Metallurgical examination revealed that the engine’s crankshaft fractured due to fatigue cracks that developed as a result of the No. 2 main bearing shifting in the crankcase saddle. The through-bolts that clamp the No. 2 crankcase saddle faces are secured with the hold-down nuts for the Nos. 2 and 3 cylinders. The engine had a reported total time in service of 6,629 hours with 1,475 hours since major overhaul. All six cylinders had been replaced since the overhaul, with the Nos. 2 and 3 cylinders having been replaced 692 and 549 hours before the accident, respectively.