Accident Overview
A commercial pilot and an FAA check pilot were conducting a Part 135 check flight in a McDonnell Douglas (Hughes) 369D rotorcraft. The commercial pilot, who had 900 hours of pilot-in-command time in the make and model, occupied the left seat as the examinee. The check pilot, with 40 hours of PIC time in the make and model, occupied the right seat.
Sequence of Events
After returning to the Boise airport, the commercial pilot transferred control of the aircraft to the check pilot, who then demonstrated a simulated 180-degree autorotation. The check pilot rolled off power, after which the GEN OUT caution light illuminated, followed by the ENG OUT warning light. The check pilot noted that rotor RPM remained in the green, but engine RPM was decelerating. The commercial pilot reported that he felt the check pilot's flare was premature. The rotorcraft landed hard, and during the impact, the main rotor blades flexed downward, striking and severing the tailboom.
Post-Crash Examination
Examination of the rotorcraft after the accident revealed that the throttle/collective controls from both the left and right seats to the engine fuel control unit had been misrigged. A test run of the engine confirmed a flameout condition when the right seat throttle was retarded to the idle position.
Maintenance History
A review of the rotorcraft's maintenance log showed that the right seat controls had been installed two days before the check flight. The installation had been signed off with the notation that "all rigging found to be within limits." No further details about the maintenance procedure were available.
Flight Manual Guidance
The McDonnell Douglas MD500D Rotorcraft Flight Manual, in its Normal Procedures Section, specifies that a throttle rigging check must be performed prior to autorotation training. This check must be conducted on both left and right seat throttle controls if dual controls are installed. The manual also includes a warning that misrigging of the throttle control may result in inadvertent flameout during rapid closing of the twistgrip to the ground idle position.