What happened
On July 12, 2013, a Gaz’aile ultralight, registration F-PTML, was performing a training flight at a private airfield in Sabonneredes, France. The pilot, who had built the aircraft, invited a known instructor to conduct the flight to extend the pilot's single-engine piston (SEP) class rating. Due to the unavailability of the originally planned aircraft, the flight was conducted in the owner's self-built machine.
The pilot elected to take off from runway 27. During the takeoff roll, the pilot reached rotation speed at approximately 52 knots. However, following rotation, the aircraft failed to accelerate. The aircraft remained in ground effect until the end of the runway, where it crossed a road and entered an adjacent field. The aircraft traveled approximately 40 meters into the field before the landing gear collapsed, causing the aircraft to come to a stop. There were no injuries to the pilot or the instructor, but the aircraft was heavily damaged.
The investigation
The investigation focused on the aircraft's performance capabilities and the flight preparation. The aircraft was operating at a weight near its maximum takeoff mass, with the center of gravity positioned at the rear limit of the manufacturer's defined envelope.
While the flight manual specifies a rotation speed of 52 to 55 knots (depending on mass) and requires maintaining a level acceleration phase until reaching 60 knots before climbing to 73 knots, the investigation noted that the aircraft's takeoff distance is highly sensitive to environmental factors. The manufacturer's theoretical takeoff roll for the day's conditions—including a grass runway, uphill slope, high temperature, and pressure altitude—was estimated at approximately 600 meters, which exceeded the available runway length.
Findings
- The primary cause of the accident was the improvisation of a training flight and inadequate flight preparation.
- The high takeoff mass of the aircraft, given the specific environmental conditions, should have prompted the instructor to cancel the flight due to the limited runway length.
- The instructor's lack of familiarity with the specific performance characteristics of this aircraft contributed to the decision to proceed.
- Mutual trust between the two pilots influenced the decision to undertake the flight despite the risks.
Safety action
- It is suggested that a reminder regarding the necessary corrections for calculating aircraft performance could be included in the flight manuals of non-certified aircraft. This would assist pilots in accounting for the impact of meteorological conditions (temperature, wind) and airfield characteristics (runway surface, slope, and pressure altitude) when operating on limiting runways.