What happened
On Sunday, 25 June 2023, at approximately 12:06 UTC, a Grumman American AA-5A Cheetah departed from runway 24 at Goetsenhoven aerodrome (EBTN) for a non-commercial cross-country flight to Genk/Zwartberg. The aircraft had already flown earlier that day under hotter conditions without incident. For this second flight, the pilot carried two passengers: a female in the front right seat and her husband in the rear right seat.
After taxiing to the runway threshold, the aircraft performed a rolling takeoff to accommodate another aircraft on base leg. The pilot rotated at roughly 60 KIAS but immediately noticed a lack of expected acceleration and climb performance. Recognizing that returning to the runway was no longer feasible, he attempted to clear the road bordering the airfield by maintaining altitude. However, the aircraft suddenly descended steeply and impacted a cultivated field beyond the runway, landing on its main gear before veering right. All occupants evacuated quickly; the pilot sustained no injuries, while the passengers suffered minor abrasions and contusions.
The investigation
The AAIU(Be) conducted a limited-scope fact-gathering investigation focusing on the immediate circumstances of the occurrence. Data from the onboard GNSS logger confirmed the aircraft's trajectory and ground-roll acceleration. Witness statements, including those from experienced pilots and a vehicle driver nearby, corroborated that the aircraft adopted an abnormally high nose attitude shortly after liftoff and appeared to "hang" on engine power before descending. The stall warning horn was not heard by occupants or witnesses.
Maintenance records showed the aircraft was airworthy with a recent 50-hour inspection completed in June 2023. Mass and balance calculations confirmed the aircraft was within limits, though the center of gravity was aft. The pilot held a valid PPL(A) but had last flown more than a month prior and had not carried rear passengers recently.
Findings
The investigation determined that the aircraft remained on the backside of the power curve during the initial climb, unable to accelerate or climb effectively. A nose-up elevator trim setting, combined with an aft center of gravity, increased pitch sensitivity and adversely affected acceleration. This configuration, coupled with elevated ambient temperatures reducing performance, created a situation the pilot did not recognize in time. The period of inactivity and the altered flight control feel due to passenger weight distribution likely contributed to the delayed recognition of the stall risk. Two minor injuries were sustained by the passengers.
Safety action
The AAIU(Be) issued a safety message highlighting the risks of operating on the backside of the power curve during takeoff, particularly regarding elevator trim settings and passenger weight distribution. The investigation referenced existing safety leaflets from the French IASA on this topic, urging the pilot community to remain vigilant about pitch attitude and airspeed management after rotation.