What happened
On 1 June 2000, a CASA 1.131-E3B, registration G-BXBD, was conducting a flight test to renew its Permit-to-Fly following a significant restoration. The flight, which included the pilot and an engineer, had been underway for approximately one hour when the pilot applied moderate negative 'g' forces. At this moment, the engine ceased operation.
In an attempt to restore power, the pilot performed a dive and advanced the throttle, but the engine failed to restart. At an altitude of roughly 1,000 feet and an airspeed of 120 knots, the pilot declared a 'Mayday' and prepared for a forced landing in a nearby field. The chosen landing site was subject to a slight crosswind and contained power cables at the upwind end. The pilot planned to land further down the field to ensure sufficient clearance.
As the aircraft approached the landing site, the rate of descent proved higher than expected, partly due to the aircraft being heavier than during previous glide practice. While the aircraft successfully cleared the first set of wires, the crew encountered a second set of cables running perpendicular to their path, which had been obscured by trees and a boundary hedge. Lacking the altitude or speed to fly over these wires, the pilot attempted to fly beneath them. During this maneuver, the aircraft struck trees and pitched nose-first into the ground. There were no injuries to the two occupants.
The investigation
The investigation focused on the cause of the engine failure and the circumstances of the landing. Investigators examined the fuel system of the CASA 1.131-E3B, which utilizes a single tank with two distinct outlets. One outlet is used for priming and reserve, while the 'OPEN' position utilizes a 'flop' tube designed to maintain fuel flow during negative 'g' maneuvers.
It was established that the fuel selector had not been moved to the 'OPEN' position. Because the selector remained in the 'RESERVE AND PRIME' position, the fuel supply was susceptible to interruption during maneuvers. The investigation also noted that while the flight manual's instructions regarding the selector were part of pre-start checks, there was no explicit requirement in the manual to switch to 'OPEN' after the engine had started.
Findings
- The engine failure was caused by the fuel selector being left in the 'RESERVE AND PRIME' position, which prevented a continuous fuel supply when negative 'g' forces were applied.
- The pilot and engineer both failed to switch the selector to the 'OPEN' position prior to the maneuver.
- The aircraft's higher weight compared to previous practice contributed to a higher-than-anticipated descent rate.
- The presence of obscured power cables prevented a safe landing clearance.