What happened
On 18 March 2004, a X'Air Falcon 133(1), registration G-CCNL, was conducting flight testing near Ham, Taunton, Somerset. The mission involved a BMAA test pilot attempting to collect position error correction data and measure stick forces during a 2g Vmax descending turn. While the aircraft was maintaining the required 2g load for approximately six seconds, the engine ceased operation and failed to restart despite throttle inputs.
The crew, having planned the manoeuvre over a large field, attempted a forced landing into the wind. However, the discovery of power lines crossing the field prevented them from orbiting to find a safer landing spot or flying beneath the wires. To lose altitude quickly, the crew performed a side-slip. During the final approach, the aircraft's airspeed was higher than the crew realized, as the wing-mounted pitot-static system was underreading. This caused the aircraft to float during the flare, touching down with only 60 metres of runway remaining. The aircraft ultimately struck a boundary hedge at approximately 10 kt, resulting in no injuries but causing slight damage to the landing gear.
The investigation
The investigation focused on why the engine failed during the high-load manoeuvre and why the approach speed was misjudged. Investigators examined the aircraft's pitot-static system and the carburettor design. It was noted that the pilot was accustomed to a cockpit-mounted system, which is more accurate, whereas the wing-mounted system used during this flight was prone to underreading.
Regarding the engine, the investigation identified a mechanical issue within the PHBE36HS carburettor. The twin floats in the single fuel bowl were connected to the same arm, preventing independent movement. During the high-g turn, this configuration allowed the fuel level in the bowl to drop below the level required to feed the fuel jet.
Findings
- The engine failure was caused by fuel starvation resulting from a carburettor float level issue.
- The interconnected twin-float arm design allowed the fuel level to fall too low during extreme manoeuvres.
- The pilot misjudged the approach speed because the wing-mounted pitot-static system underread the actual airspeed.
- The presence of power lines restricted the crew's ability to execute a safer landing pattern.