Enstrom F-28F N785M

Summary

On 6 March 2007 at about 19:00 local time, a Enstrom F-28F registered N785M was involved in an accident near Monmouth, Oregon, United States. One person was on board and nobody was injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

6 March 2007 at 19:00

Classification

Accident

Location

Monmouth, Oregon, United States

Coordinates

44.0833, -123.0000

Aircraft

Enstrom F-28F

Registration

N785M

Category

Helicopter

Engines

1

Operator

Not recorded

Operating rule

Part 137: Agricultural

Purpose of flight

Aerial Application

Phase of flight

Not recorded

Route

Monmouth → Corvalis

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

LAX07LA106

Nobody was injured.

The failure of the main drive belt tension assembly shaft due to high cycle, low stress fatigue.

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

Read the full NTSB narrative

The pilot reported that he was spraying Christmas trees, when the engine experienced an over speed condition and he "lost all power to the transmission." The pilot initiated a forced landing to a field. During the forced landing, the helicopter touched down hard and bent the tail boom. The pilot stated that the engine was producing power, but it wasn't being delivered to the rotor blades. Examination of the helicopter revealed the shaft of the main drive belt tension assembly was fractured, which resulted in the main drive belt disengaging from the transmission. Materials examination of the shaft showed that the shaft fractured due to high cycle, low stress fatigue. The fatigue initiated from multiple origins at the thread root. No material defects specific to the origin were noted, but overall hardness values suggested that the shaft strength was less than typical strength values for the specified material. It remained undetermined whether the strength was above the design minimum since no material specifications for the shaft could be produced by the manufacturer.

Quoted verbatim from the NTSB record.