What happened
On March 6, 2010, an Alon A2-A (Aircoupe), registration CS-AIG, departed from a private airstrip at Herdade “Pinheiro e Cavaleiro” in Ciborro, Portugal, for a planned local flight. The flight was intended to last approximately one hour.
During the takeoff roll, the aircraft encountered a strong tailwind. While the pilot successfully lifted the aircraft off the runway, the plane was unable to accelerate to the required safety speed of 65 MPH. The aircraft entered a state of power inversion, where the engine could not provide enough thrust to maintain altitude while simultaneously increasing airspeed. As the pilot attempted to lower the nose to gain speed, the aircraft lost altitude, forcing the pilot to pull back on the controls, which in turn caused the aircraft to lose further airspeed. This resulted in an unstable, oscillating flight pattern at the edge of a stall. Eventually, the aircraft struck the ground approximately 300 meters beyond the end of the runway, impacting the terrain and flipping inverted. Both the pilot and the passenger sustained fatal injuries.
The investigation
The GPIAAF investigation focused on the aircraft's performance capabilities and the mechanical condition of the engine. Investigators examined the takeoff procedures, noting that the pilot followed the Aircraft Flight Manual (AFM) procedures but lacked specific performance correction charts for the prevailing tailwind conditions.
Technical analysis of the Continental C90 engine revealed that it was not producing its rated nominal power. The investigation found that cylinder compression levels were below the minimum required standards and identified corrosion on several critical engine components. Furthermore, the investigation noted that the aircraft had not undergone specific maintenance recently, despite having completed an annual inspection several months prior.
Findings
- The primary cause of the accident was the aircraft's inability to maintain flight due to being airborne at the minimum sustentation speed and being unable to accelerate without losing altitude.
- Engine power deterioration due to low cylinder compression and internal corrosion significantly contributed to the loss of performance.
- The takeoff was performed with a strong tailwind without the use of necessary performance correction calculations, a practice discouraged by the manufacturer's manual.
- The aircraft's inability to climb was exacerbated by the lack of sufficient airspeed to exit the power inversion zone.