Accident Sequence
The purpose of the flight was to provide an introductory flight to a potential student. The flight instructor, a certified flight instructor (CFI) with 6,271 hours of experience, conducted a preflight inspection step by step following the checklist. The inspection included examination of the swash plate assembly for security of the flight control push/pull tubes. The student reported no preflight inspection discrepancies.
After engine start, the helicopter departed to the west, climbing to 500 feet mean sea level (msl), then descending to 300 feet. While flying straight and level at 60 knots, the student, who was looking outside, reported that the helicopter banked left and pitched nose down, making it impossible for the instructor to control the aircraft. The CFI commented several times "what happened" and attempted to recover from the left and nose down attitude but was unable. The CFI moved the cyclic control in an attempt to recover, but due to his confusion, the student could not recall what position the cyclic was moved to. The student perceived the helicopter impacted the ground first with the left skid. The student did not notice any change in engine sound from takeoff to the moment the helicopter banked left.
Postaccident Examination
Postaccident examination of the helicopter revealed that the left forward push/pull tube was not connected to the swashplate assembly; the lug was not fractured. The rod-end and securing hardware of the left push/pull tube were not located. The securing hardware for the aft push/pull rod to the swashplate assembly was found to be loose; the threads of the bolt did not extend beyond the end of the nut, and a palnut was not in position. NTSB examination of the swashplate assembly found no elongation of the hole of the left forward lug, but linear impressions on the interior surface were consistent with the threads of the bolt. The impressions were located in the area where the bolt shank is normally located.
Maintenance History
Four days before the accident, tracking and balancing of the main rotor had been accomplished. The bracket used during the tracking procedure was installed to the left and aft lugs of the swashplate assembly, contrary to the procedure specified in the maintenance manual. The mechanic who performed the work could not recall if he used a new metal self-locking nut when reinstalling the push/pull rods.
Robinson Helicopter Company personnel reported that if either of the forward push/pull tubes were to become disconnected at the lower swashplate, it is assumed that the helicopter would be uncontrollable.
Postaccident review of the operator's facility and several helicopters by NTSB and FAA personnel revealed several had the push/pull tubes installed on the incorrect side of the lugs at the swashplate assembly, and the securing hardware was incorrectly installed. Additionally, FAA personnel noted discrepancies with the maintenance records. One of the helicopters with incorrectly installed push/pull tubes had been previously inspected on five separate occasions by one of the mechanics who had performed the last tracking and balancing of the main rotor on the accident helicopter.
Installation of the bracket used during the last main rotor tracking and balancing required the removal of the bolts at the left and aft lugs of the swashplate. Proper installation of the bracket requires removal of hardware that secures two of three flight control push/pull tubes to the swashplate.