What happened
On 30 August 2002, a Jabiru UL-450, registration G-TULL, was conducting a private flight intended for slow flying practice and a short cross-country route. During the descent toward the departure airfield in Milton-Under-Wychwood, the pilot engaged the carburettor heat and maintained this setting until the final approach phase.
As the aircraft reached approximately 20 feet above ground level and 200 yards from the airfield boundary, the engine ceased operation. Shortly thereafter, at an altitude of roughly 10 feet, the aircraft's flaps retracted without command, causing the aircraft to drop. In an attempt to recover, the pilot applied significant back pressure on the control stick, which resulted in a stall and a subsequent hard impact with the ground. The pilot sustained no injuries, though the aircraft suffered a cracked fuselage and damage to the right wing and left landing gear.
The investigation
Investigators examined the engine performance and meteorological conditions, noting that the pilot had previously experienced engine issues due to carburettor icing. Analysis of Met Office data, including temperature, dew point, and humidity, confirmed that conditions were consistent with a high probability of serious carburettor icing during descent power.
Regarding the flap mechanism, the investigation found that the pilot had experienced uncommanded flap retractions on four prior occasions during slow flight at altitude. Records from the Popular Flying Association (PFA) indicated that during initial test flights for the aircraft's Permit To Fly, both engine failures and flap retractions had occurred. While adjustments had been made to the carburettor idle stop and the flap handle pivot bolt to address these issues, the investigation noted that uncommanded flap retractions are a known issue in this aircraft type, often attributed to improper rigging or adjustment of the flap operating system.