What happened
On 14 November 2002, a Gulfstream AA-5A Cheetah, registration G-BGVW, was taxiing for a ferry flight to Blackbushe when the pilot noted symptoms of potential carburettor icing. During a delay of approximately seven minutes before takeoff, the pilot attempted to clear the icing by increasing engine power and applying carburettor heat. While stationary on the runway, the pilot again applied carburettor heat at 2,000 rpm.
During the takeoff roll, the engine reached 2,200 rpm, and the aircraft began its climb at a rate of slightly less than 500 fpm. However, upon reaching 200 feet above the airfield, the engine rpm dropped to 1,800 despite the application of full power. Unable to maintain level flight, the pilot performed a forced landing in a ploughed field located roughly half a mile northwest of the airfield. Upon impact, the noseleg of the aircraft collapsed, causing the plane to pitch onto its back. The single occupant sustained minor injuries and escaped through the canopy.
The investigation
Investigators examined the engine and fuel systems following the accident. The engineering inspection identified a significant presence of water within both the carburettor float chamber and the electric fuel pump. While the aircraft's wing fuel caps were found to be in good condition, the investigation of the fuel drain system revealed that one of the two drain holes in each wing fuel drain was blocked. Although the remaining unblocked hole allowed for drainage, the pilot had previously noted water during pre-flight checks and had continued draining until the water appeared to be gone.
Findings
- The aircraft had been parked outside for six weeks prior to the flight with the fuel tanks approximately two-thirds full.
- Although atmospheric conditions (temperature of +10°C and dew point of +7°C) were conducive to serious carburettor icing, the evidence suggests water contamination of the fuel was the more probable cause of the engine power loss.
- The presence of water in the fuel pump and float chamber, combined with the recent period of inactivity, points to moisture ingress or condensation within the fuel system.