Incident
During a test flight, the aircraft encountered an elevator system oscillation while in a high speed dive outside the normal operating envelope. The oscillation lasted 17 seconds and was recorded on the cockpit voice recorder with an average frequency of 28 Hz. The aft elevator sector clevis (part number 2331510-32) fractured due to reverse bending fatigue caused by the vibration, resulting in a complete loss of elevator control.
The flight crew reported that pitch control was established by using horizontal stabilizer pitch trim. During final approach to runway 17, which was 13,337 feet long by 200 feet wide, dry asphalt, the aircraft's nose began to drop. The flying pilot was unable to raise the nose using a combination of horizontal stabilizer trim and engine power. The aircraft landed short of the runway, striking an airport perimeter fence and a berm. Surface winds were from the south at 23 knots, gusting to 32 knots.
Investigation
The investigation identified the probable cause as the PIC's delayed remedial action during the elevator system oscillation, resulting in the failure of the aft elevator sector clevis due to reverse bending fatigue caused by vibration, and subsequent loss of elevator control. Factors contributing to the accident were high and gusting winds, the crosswind, the airport perimeter fence, and the berm.