Bell 407 N917AL

Summary

On 4 May 2001 at about 21:16 local time, a Bell 407 registered N917AL was involved in an accident near Vermillion 44, United States. 2 people were 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

4 May 2001 at 21:16

Classification

Accident

Location

Vermillion 44, United States

Coordinates

29.4333, -92.5000

Aircraft

Bell 407

Registration

N917AL

Category

Helicopter

Engines

1

Operator

Not recorded

Operating rule

Part 135: Air Taxi & Commuter

Phase of flight

Not recorded

Route

Hi-338 → Intercoastal

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

FTW01FA115

Nobody was injured.

Failure of the engine-to-transmission driveshaft coupling due to fatigue.

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

Read the full NTSB narrative

While in cruise flight, the pilot reported that a "slight vibration became noticeable." After a few minutes, the vibration became more pronounced, and was accompanied by a noise. During an attempted precautionary landing to an offshore platform, the vibration and noise level increased again, and total engine power was lost. The pilot then initiated an autorotation to the water, deployed the skid floats, and landed safely. While the helicopter was being towed in the water, the helicopter rolled inverted. Examination of the helicopter after recovery revealed that the KAflex engine-to-transmission driveshaft was fractured, and the forward tail rotor driveshaft segment was separated. Examination of the KAflex driveshaft revealed fatigue fractures that originated from a bolt hole in the first flex frame of the coupling at the transmission end of the shaft and fatigue fractures in the end fitting at the transmission end. The primary fracture was a fatigue crack that occurred in a bolt hole where a bolt joined the first flex frame to the center flex frame. The driveshaft was determined to be manufactured within engineering specifications. The fractured tail rotor driveshaft showed evidence of torsional overstress. The KAflex driveshaft coupling had a total time of 2,114.2 hours and an airworthiness life limit of 5,000 hours. Following the accident, the manufacturer issued a service bulletin introducing a new KAflex driveshaft with a 1,250-hour overhaul interval.

Quoted verbatim from the NTSB record.