What happened
On 30 December 2006, a Diamond DA 40 D, registration G-ZANY, was conducting a private handling exercise near Hanningfield Reservoir, north-west of Southend Airport. The flight was part of a return journey from Staple/ford to Lydd. During the exercise, the pilot performed a series of manoeuvres, including a clean stall and recovery, followed by a series of steep turns.
While executing a steep left turn at a load factor of approximately 2g, the engine experienced a momentary shudder and a propeller overspeed. Shortly after, the engine suffered a significant loss of power. The pilot attempted to switch between the two independent Engine Control Unit (ECU) channels, but the engine failed to respond to power lever changes. An emergency was declared to Southend Airport, and the pilot attempted an emergency landing in a field. The aircraft touched down long and struck a boundary hedge and a small ditch, causing the nose gear to collapse and resulting in damage to the front of the aircraft, the nose gear, and the left wing. The two occupants were uninjured.
The investigation
The AAIB examined the aircraft's fuel system, engine, and ECU data logs. The investigation found that the fuel filter canister contained only a very small amount of fuel, which was insufficient for normal operation. While the fuel tanks themselves were intact, the gascolator drain valve was found to be damaged and leaking.
Engine manufacturer tests were conducted in Germany to replicate the flight conditions. These tests involved performing steep turns with varying levels of fuel and introducing air into the fuel supply. The tests demonstrated that while the engine could tolerate small air bubbles, larger 'slugs' of air caused the engine to run down and stop. Furthermore, the investigation looked into whether the fuel could have moved away from the pickup point during unbalanced turns.
Findings
- The engine experienced a sudden drop in fuel rail pressure, falling to 130 bar, which is consistent with fuel starvation.
- The small volume of fuel found in the fuel filter canister suggests the engine was deprived of its fuel supply.
- There was evidence suggesting that air may have been introduced into the fuel system, though the exact mechanism could not be confirmed.
- The ECU data showed that the engine functioned normally until the moment of power loss, and no mechanical or electrical failures were identified in the engine or ECU.