What happened
On 1 February 2022, a Jabiru UL-450, registration G-CBGR, was performing a private flight at Clench Common Airfield in Wiltshire. During the final stages of the approach to landing, at an altitude of approximately 40 feet, the aircraft's flaps retracted without input from the pilot.
Upon noticing the retraction, the pilot attempted to raise the aircraft's nose to compensate for the sudden loss of lift. However, the pilot was unable to prevent the aircraft from striking the ground with significant force. The impact caused extensive damage to the airframe, including a shattered windscreen, a damaged fuselage, and a detached right wing. The nose undercarriage leg sheared off during the collision, and the main undercarriage legs also failed. The incident resulted in one serious and one minor injury to the crew.
The investigation
Investigators examined the mechanical operation of the aircraft's manual flap system. On this model, the flaps are controlled by a lever mounted on the side wall, which uses a button to latch into three distinct positions. The investigation focused on why the lever moved from its selected position during the approach.
It was established that the aircraft had recently undergone an engine service and the installation of a new instrument panel. While the aircraft had been tested in recent flights, the investigation looked into the stability of the flap control mechanism. The pilot noted that the aircraft encountered some turbulence shortly before the retraction occurred.
Findings
- The primary cause of the accident was the flap handle becoming dislodged from its selected gate, which triggered the uncommanded retraction of the flaps.
- The loss of lift caused by the large flaps retracting (covering roughly 70% of the wing span) led to a rapid change in aircraft attitude that could not be corrected at such a low altitude.
- The investigation highlighted a known design vulnerability: if the flap handle pivot bolt is not sufficiently tightened, the handle can jump the gate. This specific risk is documented in the Light Aircraft Association type acceptance data sheet for this aircraft type.