History of the Flight
On 30 August 2002 at 1900 hours UTC, a Jabiru UL-450, registered G-TULL, was on a private flight piloted by its owner. The purpose was to practice slow flying with and without flaps, followed by a short cross-country. During the descent into the departure airfield, the pilot selected carburettor heat and left it selected until turning onto final approach. At approximately 20 feet above ground level (agl) and 200 yards from the airfield boundary, the engine stopped. At around 10 feet agl, within the airfield boundary, the flaps retracted and the aircraft dropped. The pilot pulled back on the control stick, which precipitated a stall, followed by a hard impact with the ground.
Injuries and Damage
The pilot, the sole occupant, reported no injuries. The aircraft sustained damage including a cracked fuselage, a broken right wing, and a broken left landing gear.
Engine
The pilot believed the engine failed due to carburettor icing, which he had experienced on three previous occasions at altitude. On each of those occasions, he successfully restarted the engine using carburettor heat. A meteorological aftercast from the Met Office, plotted on a Carburettor Icing Probability Chart using temperature, dew point, and humidity, indicated that serious carburettor icing could occur at descent power.
Flaps
The pilot reported that the flaps had retracted uncommanded on four previous occasions while flying the aircraft, all occurring during slow flight at altitude.
Test Flights for Permit To Fly Certificate
During test flights conducted by the Popular Flying Association (PFA) for the initial issue of the Permit To Fly Certificate, the aircraft experienced both engine failures and uncommanded flap retractions. The idle stop on the carburettor was reset to prevent stalling when the throttle was fully closed, and the flap handle pivot bolt was adjusted to prevent it from jumping out of its detent. Subsequent test flights were completed without recurrence of engine failure or flap retraction.
Other Information
Enquiries with the PFA revealed that there have been several reports of uncommanded flap retractions on this aircraft type, most of which were attributed to incorrect adjustment or rigging of the flap operating system. The Civil Aviation Authority (CAA) had not received any reports of uncommanded flap retractions on this type. According to a PFA Inspector and pilot familiar with the aircraft type, approaches must be flown quite flat to keep airspeed under control, and the aircraft tends to float during the landing flare.