Bell 206B II N70711

Summary

On 15 August 1998 at about 00:55 local time, a Bell 206B II registered N70711, operated by Alaska State Troopers, was involved in an accident near Chickaloon, Alaska, 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

15 August 1998 at 00:55

Classification

Accident

Location

Chickaloon, Alaska, United States

Coordinates

61.7407, -148.2207

Aircraft

Bell 206B II

Registration

N70711

Category

Helicopter

Engines

1

Operator

Alaska State Troopers

Operating rule

Part 91: General Aviation

Purpose of flight

Public Use

Phase of flight

Not recorded

Route

Willow → Unknown

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

ANC98TA125

Nobody was injured.

A fracture of the main rotor drag pin assembly.

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

Read the full NTSB narrative

The commercial helicopter pilot said that he had completed a normal, westerly approach, and subsequent landing atop a 4,000 feet msl mountain. The pilot stated that as he reduced the throttle to the flight idle position, in preparation for engine shut down, a severe airframe vibration occurred. A postaccident inspection revealed that the helicopter's main rotor transmission had been torn from the lower isolation mount assembly, and the helicopter's transmission deck sustained substantial damage. The main rotor drag pin assembly, main rotor driveshaft, forward coupling assembly, and associated fasteners, were sent to the NTSB Materials Laboratory for inspection. The inspection discovered no evidence of a progressive fracture mechanism, and all fracture faces displayed features typical of overstress separation. The main rotor transmission isolation mount was retained by the NTSB, and sent to the manufacture for evaluation, and testing. An FAA airframe certification engineer attended the evaluation process, and reported that the isolation mount operated slightly below acceptable stiffness limits. He added that since the isolation mount sustained damage during the accident, an accurate stiffness value was unattainable.

Quoted verbatim from the NTSB record.