Bell UH-1B N3979C

Summary

On 23 September 1993 at about 15:15 local time, a Bell UH-1B registered N3979C, operated by Clearwater Management Co. Inc., was involved in an accident near Pierce, Idaho, 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

23 September 1993 at 15:15

Classification

Accident

Location

Pierce, Idaho, United States

Coordinates

46.1604, -116.9201

Aircraft

Bell UH-1B

Registration

N3979C

Category

Helicopter

Engines

1

Operator

Clearwater Management Co. Inc.

Operating rule

Part 133: Rotorcraft Ext. Load

Purpose of flight

Other Work Use

Phase of flight

Not recorded

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

SEA93LA207

Nobody was injured.

SEPARATION OF THE 90 DEGREE GEARBOX AFTER FATIGUE FAILURE OF THE GEARBOX ATTACH BOLTS. FACTORS INCLUDE HILLY/MOUNTAINOUS TERRAIN.

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

Read the full NTSB narrative

WHILE MANEUVERING NEAR A REFUELING SITE IN HILLY/MOUNTAINOUS TERRAIN, THE 90 DEGREE GEARBOX SEPARATED FROM THE AIRCRAFT. THE PILOT THEN ATTEMPTED A RUN-ON FORCED LANDING ON A NEARBY LOGGING ROAD. DURING THE FLARE, THE AIRCRAFT LANDED HARD, RESULTING IN A COLLAPSE OF THE SKIDS, AND SEPARATION OF THE REMAINING PORTION OF THE TAIL BOOM. METALLURGICAL ANALYSIS REVEALED THAT ALL SIX GEARBOX ATTACH BOLTS HAD EXPERIENCED REVERSE-BENDING FATIGUE FAILURE. THE OPERATOR RECORDS INDICATED THAT THIS WAS A NEW SURPLUS PART WHICH HAD 136 HOURS OF OPERATION SINCE NEW. HISTORICAL RECORDS CONFIRMING THE UNIT'S TOTAL TIME SINCE BEING SHIPPED TO THE PHILIPPINES AS A NEW SURPLUS PART IN 1981 COULD NOT BE LOCATED.

Quoted verbatim from the NTSB record.