What happened
On May 26, 2015, at 18:20 UTC, a Dyn’Aero MCR 4S-2002, registration PH-VGH, was performing a local private flight at the Vilar de Luz aerodrome in Água Longa, Santo Tirso, Portugal. The aircraft was executing left-hand traffic patterns for runway 34.
As the pilot completed the turn from the base leg to the final approach, the aircraft suddenly rolled uncontrollably to the left. The aircraft entered a left-hand spiral and impacted a paved road leading to a football field. The impact resulted in two fatalities and the total destruction of the aircraft.
The investigation
The GPIAAF investigation focused on the flap control system to determine why the aircraft lost control during the approach. Investigators examined the rod and nut assembly, performing visual, laboratory, and microscopic analyses (including scanning electron microscopy).
The investigation established that the aircraft was operating within mass and balance limits and that the engine was producing power at the time of impact. However, the investigation found that the pilot lost control due to asymmetric flaps. The analysis revealed that while the right flap extended normally to its 30-degree limit, the left flap failed to extend or suddenly retracted.
Findings
- The primary cause of the accident was a failure in the flap actuator system caused by the failure of a bronze nut.
- The bronze nut on the left side of the flap control system had worn beyond the limits specified by the manufacturer.
- The owner had failed to comply with Airworthiness Directive F-2013-001, which required the replacement of this specific bronze nut.
- The Dutch Civil Aviation Authority had revalidated the aircraft's Special Airworthiness Certificate without verifying the actual condition of this component.
- The failure occurred at a low altitude, leaving the pilot with insufficient time to recover from the resulting asymmetric lift and roll.