Bell UH-1B N46969

Summary

On 5 December 2007 at about 23:00 local time, a Bell UH-1B registered N46969 was involved in an accident near Ennis, Montana, 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

5 December 2007 at 23:00

Classification

Accident

Location

Ennis, Montana, United States

Coordinates

44.7961, -111.6247

Aircraft

Bell UH-1B

Registration

N46969

Category

Helicopter

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Positioning

Phase of flight

Not recorded

Route

Ennis → Ennis

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

SEA08LA043

Nobody was injured.

The loss of collective control friction during takeoff that resulted in a collective bounce oscillation. Contributing to the accident was the pilot's failure to maintain aircraft control during the aborted takeoff and the snow covered terrain.

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

Read the full NTSB narrative

The pilot reported that he had flown the helicopter for five cycles throughout the day and landed at the landing zone to remove the long line. He was asked by ground personnel to reposition the helicopter from the landing zone to a nearby road in order for a snowplow to access the landing zone. Once the snowplow was done, the pilot began to reposition the helicopter back to the landing zone. As the helicopter lifted from the ground, it began to vibrate, and the vibration turned into a severe "hop or a bounce." The pilot lifted the helicopter to 15 feet; however, it continued to vibrate and subsequently began to nose over and become uncontrollable The pilot then decided to force land the helicopter and touched down hard in two feet of snow, substantially damaging the doorframe. Inspection of the helicopter revealed that the collective control absolute friction was less than the manufacturer's specified setting and the maintenance manual indicated that if the friction is not set properly, a collective bounce could be induced. No other mechanical anomalies were identified and the reason for the loss of friction could not be determined. The operator's manual indicates that the severity of this oscillation is such that effective control of the helicopter may become difficult to maintain.

Quoted verbatim from the NTSB record.