Cessna U206G N9742Z

Summary

On 5 December 2010 at about 20:30 local time, a Cessna U206G registered N9742Z was involved in an accident near Leverett, Massachusetts, United States. 4 people were on board and 2 died, 2 were seriously injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

5 December 2010 at 20:30

Classification

Accident

Location

Leverett, Massachusetts, United States

Coordinates

42.4442, -72.4919

Aircraft

Cessna U206G

Registration

N9742Z

Category

Airplane

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Personal

Phase of flight

Not recorded

Route

Keene → Islip

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

ERA11FA078

2 people died.

A total loss of engine power due to the fatigue failure of the crankshaft, which resulted from improper tightening of the cylinder hold-down nuts.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

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.

Quoted verbatim from the NTSB record.