Pterodactyl Ptraveller, 10-390, Fairlight Authorised Landing Area, 24 km south-west of Canberra, Australian Capital Territory, on 24 December 1989

Circumstances:

The pilot was to conduct solo training flights in a flying wing type ultralight aircraft. Directional control in this type of aircraft is achieved by yaw through the use of wing tip rudders. These rudders are spring loaded to the left and balanced by air loads in flight. During pre-flight assembly on the day of the accident, the control cable attachment to the left rudder was inadvertently positioned on the wrong side of a clamp near the wing tip rib. This allowed the cable, under some conditions to foul on the clamp. After assembling the aircraft, the pilot conducted some flights, until a heavy landing bent the main landing gear axle. The pilot used a steel pipe as a hammer to straighten the axle, but the shock loads from this operation dislodged the left hand wing tip rib and rear spar. Although an inspection was conducted, it did not discover the damage to the wing tip which would only have been apparent by removing the wing sail. On the subsequent flight at about 30 feet after take-off, the damaged left wing tip distorted due to aerodynamic loads, initiating an uncontrolled right roll. Attempts by the pilot to level the aircraft resulted in the incorrectly installed control cable attachment inducing further adverse distortion. The aircraft rolled to about 60 degrees, entered a rapid descent and clipped a parked aircraft before coming to rest in a nose down attitude. The engine which appeared to be operating normally was shut down by the pilot after the aircraft came to rest.

Significant Factors:

The following factors were considered relevant to the development of the accident:

1. Incorrect assembly of the left hand rudder cable.

2. Shock load damage to the left hand wing tip structure during straightening of the landing gear axle.

3. Inadequate inspection of the aircraft for damage.

4. The damaged left hand wing tip distorted with increased aerodynamic loads. This accident was not the subject of an on-scene investigation.