Southern Aero UH-1B N896W

Summary

On 27 August 1997 at about 16:15 local time, a Southern Aero UH-1B registered N896W was involved in an accident near Skykomish, Washington, United States. One person was on board and one died. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

27 August 1997 at 16:15

Classification

Accident

Location

Skykomish, Washington, United States

Coordinates

47.6408, -121.3296

Aircraft

Southern Aero UH-1B

Registration

N896W

Category

Helicopter

Engines

1

Operator

Not recorded

Operating rule

Part 133: Rotorcraft Ext. Load

Purpose of flight

Other Work Use

Phase of flight

Not recorded

Aircraft damage

Substantial

Weather

Unk

Light

Day

NTSB number

SEA97FA196

1 person died.

A fatigue fracture in the main rotor mast, which resulted in an in flight separation of the main rotor from the helicopter. Contributing to the accident was insufficient Federal Aviation Administration airworthiness standards and requirements for the aircraft.

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

Read the full NTSB narrative

While performing external load logging operations, the helicopter's main rotor separated from the helicopter and the helicopter crashed. Metallurgical examination of the main rotor mast revealed a fatigue fracture in the upper spirolox groove in the damper support splines. Based on the mast's historical service record, the fractured mast, a Bell part number 204-011-450-001 mast assembly with a part number '204-040-466-9' mast tube (not a valid part number according to Bell), had 4,006.7 hours at the time of the mast separation. An FAA airworthiness directive (AD), AD 97-14-12, applicable to Bell 204B, 205A, 205A-1, 205B, and 212 civil helicopters but not to surplus military UH-1 helicopters, limited the life of part number 204-011-450-001 masts to 6,000 flight hours or a retirement index number (RIN) of 300,000 (the fractured mast had a RIN of 200,335, computed according to the method specified by that AD.) The most recent main rotor mast AD directly applicable to the accident helicopter, AD 89-17-03, limited mast life to 15,000 hours and contained no requirement to establish or track RIN. The 'thin-walled' Bell part number 204-040-366-9 mast tubes installed in part number 204-011-450-001 masts were ordered removed from U.S. Army UH-1 helicopters by a 1984 U.S. Army emergency safety-of-flight message.

Quoted verbatim from the NTSB record.