Aerospatiale AS350D N57731

Summary

On 13 August 2003 at about 21:50 local time, a Aerospatiale AS350D registered N57731 was involved in an accident near Webb, Idaho, 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

13 August 2003 at 21:50

Classification

Accident

Location

Webb, Idaho, United States

Coordinates

46.3742, -116.8467

Aircraft

Aerospatiale AS350D

Registration

N57731

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

Route

Craigmont → Unknown

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

SEA03FA169

1 person was seriously injured.

An over temperature condition within the gas generator turbine which led to first stage turbine blade fatigue as well as first stage blade track warping and consequent blade tip rub. The fatigue and blade tip rub ultimately led to blade separation and failure of the engine. Contributing factors were the out of calibration condition of the turbine outlet temperature gauge and the non-operational engine CHIP warning light system. An additional factor was insufficient rotor RPM while conducting an autorotation.

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

Read the full NTSB narrative

The pilot had just maneuvered the helicopter for a water pickup for firefighting and was at an altitude of 100-150 feet above ground transitioning to forward flight (outside the height-velocity envelope) when the engine failed. He executed an autorotation to a hard landing as rotor speed bled off. Post accident examination of the engine revealed all the airfoils of the first stage turbine wheel were fractured/damaged and many of the fracture surfaces exhibited features indicative of fatigue progression. Fluorescent penetrant inspection revealed multiple cracks extending onto the rim faces and radial sectioning of several of the stage one turbine airfoils revealed intergranular cracks within the airfoils as well as cracks in the rim area consistent with exposure to temperature spikes and/or elevated operating temperatures. Examination of the second stage turbine nozzle assembly revealed evidence of both thermal distress and mechanical damage and the first stage blade track exhibited damage and deformation throughout its circumference. The diameter and run-out of both the first stage and second stage blade tracks revealed an out of round (warped) condition. Testing of the ToT gauge revealed an out of calibration condition between true input temperature and the temperature displayed on the gauge. The disparity increased as true temperature increased with the gauge reading on the low side (lower than true operating temperatures). Post accident examination revealed metal particulates bridging the contacts of the engine chip light plug. Testing of the warning system revealed a discontinuity within the airframe which prevented the chip light from operating.

Quoted verbatim from the NTSB record.