What happened
On 11 July 1999, a Pitts Special, registration N80BA, was conducting a private flight near Newtownards Airport, Northern Ireland. After flying approximately 10 miles south of the airfield, the pilot began performing various aerobatic maneuvers, including barrel rolls and climbing rolls.
While returning to the airfield, the pilot descended to 1,200 feet and reduced engine power to 1,500 RPM. At this moment, the engine ceased operation immediately. The pilot notified Newtownards of the situation and prepared for an emergency landing. Due to a high rate of descent, the pilot's options for landing sites were restricted, leading to a decision to land on a nearby hill rather than attempting a landing at sea.
During the final approach, the aircraft's speed dropped to 68 knots, causing a stall. The right wing struck a hedge, which induced a spin. The impact caused the fuel tank to rupture, drenching the pilot in fuel; however, no fire occurred. The pilot managed to exit the open cockpit and move away from the wreckage. The aircraft sustained very extensive damage, including the wings being torn from the fuselage. The pilot sustained serious injuries.
The investigation
The AAIB examined the wreckage and the engine components. While the engine itself showed no obvious cause for the stoppage, investigators noted that the Bendix Pressure Carburettor had previously undergone testing earlier in 199 and had been recalibrated due to low flow rates. The overhaul agency had previously warned that the unit's seals and gaskets were of an older type susceptible to age hardening.
Following the accident, the AAIB sent the carburettor to an overhaul agency for a detailed strip-down. Although impact damage prevented a functional flow test, the physical examination revealed that the unit had been correctly assembled and the diaphragms and seals remained intact. However, investigators noted that the internal diaphragms had become stiffer due to age. Because a flow test could not be performed, the investigators could not definitively rule out whether mild carburettor icing might have contributed to the engine failure.