Hughes 369HS N4250N

Summary

On 20 June 1997 at about 10:30 local time, a Hughes 369HS registered N4250N was involved in an accident near Pacific Ocean. 2 people were on board and one died, one was seriously injured. The aircraft was destroyed. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

20 June 1997 at 10:30

Classification

Accident

Location

Pacific Ocean

Coordinates

Not recorded

Aircraft

Hughes 369HS

Registration

N4250N

Category

Helicopter

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Other Work Use

Phase of flight

Not recorded

Aircraft damage

Destroyed

Weather

VMC

Light

Day

NTSB number

LAX97LA218

1 person died.

The unapproved field modification of the cyclic trim switch, including the use of non-standard parts, which resulted in a hard-over lateral trim failure, and the pilot's subsequent failure to maintain control of the helicopter during a landing approach. A factor in the accident was the operator's failure to comply with a factory service bulletin, which required replacement of the switch with a new version, and the pilot's continued operation with a known discrepancy.

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

Read the full NTSB narrative

The pilot was spotting tuna off a ship and was approximately 10 minutes from the ship when the cyclic went full left travel. The pilot, who had not attended any factory training courses on this helicopter, said he tried to get the trim motor to reengage but to no avail. He was unable to get the cyclic to return to a neutral position. He stated that he came in to land on the boat and lost control of the helicopter because he could not hold the cyclic with one hand. The helicopter struck an antenna, rolled to the left, and landed upside down in the water. The pilot indicated to others he had problems with the trim switch on previous flights. The owner's manual states that the cyclic stick forces with a runaway cyclic would be approximately 30 pounds. It states that the helicopter will respond normally to all cyclic inputs by the pilot. The switch was returned and disassembled for detailed examination. The manufacturer could not find any identifiable markings on the switch during the examination and tool marks and other internal evidence disclosed that the switch had been disassembled and reassembled in the field. Non-standard parts were found on the inside of the switch. Boeing Helicopters sent out a mandatory service information notice dated March 10, 1994, which required all operators of the 369/500 helicopters to replace all four-way trim switches with the revision 'D' four-way trim switch. The switch is not a repairable item. No repair manual or spare parts programs exist for this switch.

Quoted verbatim from the NTSB record.