What happened
On 13 June 2019, a Bristell NG5, registration G-OJCS, was conducting a flight near Kilrush Airfield, Co. Kildard, for the purpose of pilot familiarization. The aircraft was operated by a syndicate of three pilots. During the flight, the crew performed two stall exercises starting from an altitude of approximately 3,300 feet. While attempting to recover from the second stall, the aircraft lost controlled flight and entered a rapid descent characterized by a flat spin. The aircraft struck an agricultural field approximately 5 NM south of the airfield. The impact resulted in two fatalities and the total destruction of the aircraft.
The investigation
The AAIU examined the wreckage and confirmed that all flight control surfaces, linkages, and engine controls were intact and functional prior to the impact. Analysis of recovered electronic data confirmed that the aircraft completed two straight and level stall exercises before losing control during the second recovery attempt. The investigation also involved international cooperation with agencies from the UK and the Czech Republic.
A critical component of the investigation focused on the aircraft's weight and balance specifications. Investigators discovered that the moment arm for the pilot and passenger was actually longer than what was stated in the manufacturer's documentation available at the time of the accident.
Findings
- The aircraft entered a counter-clockwise flat spin during the recovery phase of a stall exercise.
- The weight and balance documentation provided for the aircraft incorrectly specified the moment arm for occupants as 600 mm aft of the datum.
- Independent weighing of NG5 aircraft in the UK confirmed that the actual moment arm for a pilot and passenger is longer than the 600 mm figure previously recorded.
Safety action
Following the discovery of the measurement error, the UK LAA issued airworthiness alerts to notify owners and pilots of the corrected figures. Additionally, the aircraft manufacturer issued a technical bulletin and revised the Weight and Balance sections of the Aircraft Operating Instructions to incorporate the updated crew arm measurements and a change to the weight and balance datum point.