What happened
On June 26, 2011, a Diamond DA40D, registration F-GUVQ, was conducting a cross-country flight from Clermont-Ferrand Aulnat to Cannes Mandelieu. While cruising at FL95 near the Montélimar aerodrome, the pilot observed "ECU(2) A fail" and "ECU B fail" warnings on the cockpit displays. Simultaneously, the engine experienced a severe power loss, dropping to approximately 5% of its rated output. The pilot subsequently performed a forced landing at the Montélimar aerodrome. There were no injuries resulting from the incident.
The investigation
Investigators examined the engine's fuel pressure regulation system, specifically the Prail valve (an electrovalve regulating fuel pressure in the admission manifold). Upon inspection, a wire within the Vrail plug was found to be severed inside its insulation. The investigation revealed that the insulation was crushed and the cable was bent at the point of the break.
Tracing the history of the component, investigators found that the Prail valve had been replaced in March 2009 to comply with a mandatory service bulletin. This modification required cutting wires and crimping new connectors. While the exact circumstances of that maintenance task could not be determined, it was concluded that the initial damage to the wire likely occurred during that 2009 installation. Furthermore, the maintenance facility reported that recurring ECU alarms had been appearing since December 2010, and although the valve had been replaced several times since then, the underlying wiring fault remained undetected.
Findings
- The primary cause of the power loss was the severing of a wire within the Vrail plug.
- The failure of this electrical connection caused the Prail valve to open fully, leading to a sudden drop in fuel pressure within the admission manifold.
- The engine's electrical architecture lacked sufficient redundancy; a loss of power to the valve results in a non-fail-safe condition that triggers an immediate emergency.
- The damage likely originated during a maintenance procedure in March 2009, and subsequent repeated connections and disconnections of the valve during later maintenance likely contributed to the final breakage.