What happened
On 4 February 2006, a Lambada UFM-13, registration ZU-VOS, was conducting a private flight near Port Alfred Aerodrome. The pilot, accompanied by a passenger, was performing various maneuvers along the coastline at approximately 1,500 feet. While climbing in an easterly direction at 4,000 feet, the pilot initiated a 30-degree left turn. During this maneuver, the aircraft began over-banking to the left.
In an attempt to correct the attitude, the pilot applied full right flapperon input, but the control failed to respond. The pilot then attempted to increase airspeed by pushing the control stick forward and later reduced power to idle, but the aircraft continued to spiral to the left. To maintain control, the pilot increased power and airspeed to 90 knots. During the subsequent emergency approach to Runway 10L, the left wing continued to drop sharply, resulting in a hard landing on the grass runway. The impact caused damage to the main landing gear and the propeller, though no injuries were sustained by the occupants.
The investigation
SACAA AIID investigators determined that a 3.72-meter section of the right flapperon had separated from the wing in flight. The investigation focused on the failure of the flapperon control push-pull rod, specifically finding that the rivets at the eyeball-end fitting had failed.
Technical analysis of the Dynon Avionics EFIS-D10A flight instrument revealed that the airspeed indicator was not calibrated according to the Pilot's Operating Handbook. This error caused a significant discrepancy in airspeed readings, specifically a 38% error in the Vne (never-exceed speed) display. This lack of calibration meant the pilot may have unintentionally exceeded the aircraft's structural speed limits during the maneuvers.
Findings
- The primary cause of the control surface separation was flutter occurring at high speeds.
- The aircraft's EFIS instrument provided erroneous airspeed information due to a lack of proper calibration.
- The failure of the control system was triggered by the separation of the rivets at the flapperon push-pull rod eyeball fitting.
- The pilot was flying within the perceived limits of the instrument, but the actual airspeed likely exceeded the structural design limits.
Safety action
- It is recommended that the manufacturing organization ensure all avionic equipment installations are properly calibrated to match the Pilot's Operating Handbook.
- The SACAA should consider inspections of the flapperon control systems on similar EFIS-equipped Lambada aircraft.
- Recommendations were made regarding the oversight of sub-contractor documentation and the necessity for specialized technical knowledge during the installation of modern electronic flight instruments.