Hughes OH-6A N6188L

Summary

On 25 October 2004 at about 21:25 local time, a Hughes OH-6A registered N6188L, operated by Tucson Sector Air Operations, was involved in an accident near Tucson, Arizona, United States. 2 people were on board and 2 were seriously injured. The aircraft was destroyed. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

25 October 2004 at 21:25

Classification

Accident

Location

Tucson, Arizona, United States

Coordinates

32.0064, -111.6542

Aircraft

Hughes OH-6A

Registration

N6188L

Category

Helicopter

Engines

1

Operator

Tucson Sector Air Operations

Operating rule

Public Use

Purpose of flight

Public Use

Phase of flight

Not recorded

Route

Ajo → Tucson

Aircraft damage

Destroyed

Weather

VMC

Light

Day

NTSB number

LAX05TA018

2 people were seriously injured.

The loss of engine power due to a fatigue fracture of the PC line from the governor to fuel control, resulting from fretting damage induced by excessive vibration, which was due to the failure of maintenance personnel to install the proper bearings in the starter/generator. A contributing factor was the loss of power at low altitude and airspeed (height/velocity limitation) which diminished the possibility of a successful autorotation.

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

Read the full NTSB narrative

The engine spooled down during a law enforcement surveillance flight, and the pilot made a hard forced landing in uneven terrain. The crew was performing surveillance at low altitude above an uneven wash, and the pilot was in slow sideward flight. He pulled the collective to gain altitude and airspeed to make another pass. Then he heard and felt the engine spool down. He said that it quit producing power completely, and he attempted to autorotate to the ground. He said that he had insufficient airspeed and altitude to complete a successful autorotation. The helicopter hit the ground hard in a near level attitude. It bounced backwards, and rotated 45 degrees to the right. Metallurgical examination revealed that the governor tee to fuel control PC line fractured as a result of fatigue. The tubes were bent with contours differing from the original manufactured shape, indicative of handling/assembly damage. Disassembly and inspection of the starter/generator revealed conditions indicative of wear and misassembly, including the wrong bearings being installed, which would cause the unit to operate in an out-of-balance condition and induce vibrations.

Quoted verbatim from the NTSB record.