Garlick UH-1H N94NW

Summary

On 14 December 1998 at about 19:00 local time, a Garlick UH-1H registered N94NW was involved in an accident near Darrington, Washington, United States. One person was on board and one was seriously injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

14 December 1998 at 19:00

Classification

Accident

Location

Darrington, Washington, United States

Coordinates

48.1894, -121.2105

Aircraft

Garlick UH-1H

Registration

N94NW

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

VMC

Light

Day

NTSB number

SEA99LA020

1 person was seriously injured.

The total separation of the vertical fin (stabilizer), as the result of fatigue cracks which initiated in the fourth rivet hole above where the fin extends from the tailboom.

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

Read the full NTSB narrative

While in a hover during heavy-lift aero-logging operations, the vertical fin separated from the tail boom, resulting in an uncontrolled descent into the terrain. During the investigation, the NTSB Materials Laboratory determined that the separation was due to the propagation of a number of fatigue cracks which had initiated within the fourth rivet hole above where the left side of the spar fin cap protruded from the tail boom. Although the FAA had previously issued Airworthiness Directive (AD) 97-20-09 to address the separation of vertical fins from UH-1 helicopters used in repeated heavy-lift operations, the Rotorcraft Directorate determined that the AD was not adequate. As a result, the Directorate initiated the formulation of a Priority Letter Airworthiness Directive requiring the replacement of the original fin spar with one that '...has been shown to account for the effects of repeated heavy-lift operations.'

Quoted verbatim from the NTSB record.