Flight and Accident Sequence
The flight was scheduled as a local instructional departure east from the airport, followed by a southbound cruise along the coastline. Multiple witnesses observed the helicopter at an altitude between 200 and 500 feet above ground level (agl) in straight and level flight on a south heading. One witness, a former pilot and mechanic, reported hearing a change in rotor noise, followed by a bang/pop/twang sound. Subsequently, the helicopter executed a snap-roll to the left and descended in a nose-low attitude into the terrain.
Maintenance and Inspection Findings
Post-accident examination of the flight control system revealed that the right forward servo-to-swashplate push-pull tube joint was disconnected, with the attach hardware (bolt, lock nut, two washers, and pal nut) missing. The left forward servo-to-swashplate push-pull joint was connected, but the nut was only partially engaged on the bolt threads and was finger tight; no pal nut was present. Material analysis indicated that only one of the two nuts for both the left and right connections had been installed, and that nut was only finger tight. The nut on the right servo connection rotated off during flight, allowing the bolt to extract and disconnect the servo from the push-pull tube.
Maintenance Personnel Statements
A maintenance inspection requiring disassembly of the push-pull tube-to-servo connections had been performed prior to the accident flight, followed by a 0.5-hour maintenance test flight. The mechanic who performed the inspection stated he forgot to properly secure the hardware for the left and right servo connections. He attributed the error to several factors: being pulled in all directions by company personnel since his arrival at the facility; his personal maintenance practice of ensuring reassembly was the opposite of disassembly, which was not followed; distraction from an apprentice who wanted to stay late two nights prior to complete a section of the inspection, causing the mechanic to forget to return and secure the hardware; and the company being understaffed with maintenance personnel.
Quality Control Program
The company's maintenance quality control program required that any completed maintenance be inspected by another mechanic. A review of the program indicated that mechanics were not adhering to this protocol, and the company was not providing oversight or enforcing the program.