Incident Overview
A pilot was engaged in spotting tuna from a helicopter when, approximately 10 minutes from the ship, the cyclic control abruptly moved to its full left travel limit. The pilot, who had not attended any factory training courses on the helicopter, attempted to reengage the trim motor but was unsuccessful. Unable to return the cyclic to a neutral position, the pilot proceeded to land on the boat. During landing, he reported losing control because he could not hold the cyclic with one hand. The helicopter subsequently struck an antenna, rolled to the left, and ended up inverted in the water.
Historical Issues and Manual Guidance
The pilot indicated to others that he had experienced problems with the trim switch on previous flights. The owner's manual for the helicopter states that in the event of a runaway cyclic, the cyclic stick forces would be approximately 30 pounds. It further notes that the helicopter would respond normally to all cyclic inputs made by the pilot under such conditions.
Examination of the Trim Switch
The trim switch was removed and sent for detailed examination. The manufacturer could not identify any markings on the switch. Tool marks and internal evidence revealed that the switch had been disassembled and reassembled in the field. Non-standard parts were found inside the switch, which is not a repairable item; no repair manuals or spare parts programs exist for this component.
Mandatory Service Information
Boeing Helicopters issued a mandatory service information notice dated March 10, 1994, requiring all operators of the 369/500 helicopters to replace all four-way trim switches with the revision 'D' four-way trim switch.