McDonnell Douglas 369D N8625F

Summary

On 13 November 1996 at about 00:50 local time, a McDonnell Douglas 369D registered N8625F, operated by Alika Aviation, was involved in an accident near Hana, Hawaii, United States. 5 people were 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

13 November 1996 at 00:50

Classification

Accident

Location

Hana, Hawaii, United States

Coordinates

20.7700, -155.9907

Aircraft

McDonnell Douglas 369D

Registration

N8625F

Category

Helicopter

Engines

1

Operator

Alika Aviation

Operating rule

Part 135: Air Taxi & Commuter

Purpose of flight

Unknown

Phase of flight

Not recorded

Route

Kahului → Unknown

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

LAX97LA039

Nobody was injured.

subsequent failure of the spur adapter gearshaft (SAG), after 'retaining ring to compressor impeller machining' occurred and allowed the SAG to shift aft. The mechanism which induced the ring to impeller machining was not determined. Mountainous terrain in the emergency landing area was a related factor.

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

Read the full NTSB narrative

During flight, the pilot heard a loud noise from the engine compartment, accompanied by the engine out light & horn. He entered an autorotation, & the helicopter rolled over during touchdown on mountainous terrain. Disassembly of the engine revealed the forward splines of the Spur Adapter Gearshaft (SAG), which connected the compressor & turbine module shafts, had fractured, & the compressor module was disconnected from the turbine section. The SAG retaining ring was found to have machined into the compressor impeller, which allowed the SAG to shift aft. Aft movement of the SAG then resulted in heavy wear on the splines of both the Compressor Adapter Coupling (CAC) & the SAG, which resulted in a fatigue failure of the SAG splines. The CAC & impeller were of an old configuration. Allison Commercial Engine Bulletin 1325 recommended replacement of the old CAG, SAG, impellers, & retaining rings with models of a newer design to 'improve spline wear characteristics.' Allison engineers opined that the typical retaining ring to impeller machining was due to the same retaining ring being returned to the engine during overhaul, though evidence of this was not apparent in the engine examination.

Quoted verbatim from the NTSB record.