What happened
On November 29, 2006, a Diamond DA20-A1-100 "Katana" was performing a local instructional flight at Montpellier Méditerranée airport. While the aircraft was on final approach for runway 31L at approximately 400 feet, the engine began to vibrate and subsequently stopped. At the time of the failure, the electric fuel pump and carburetor heat were both activated.
The instructor managed to restart the engine by adjusting the power lever, but the aircraft remained above the glide path. Due to the loss of power, the instructor decided to perform a landing with reduced power. Following the landing, a maintenance inspection revealed a blue fuel leak trace near the mechanical fuel pump. No injuries were reported during the incident.
The investigation
The investigation focused on the fuel delivery system, which consists of an electric pump, a mechanical pump, and a pressure sensor. Investigators examined the mechanical BING fuel pump and noted that the aircraft's electric pump delivered a discharge pressure of up to 1 bar, which significantly exceeded the mechanical pump's design specifications of 0.3 to 0.4 bar.
Technical examinations of the aircraft's engine and subsequent replacements of the mechanical pump revealed a recurring pattern of failure. After the initial incident, several replacement pumps also exhibited leaks or triggered low-pressure warnings. The investigation also reviewed similar incidents involving other aircraft equipped with Rotax 912 S3 engines and BING mechanical pumps.
Findings
- The engine failure was caused by an excessively rich fuel mixture resulting from high fuel pressure downstream of the electric pump.
- The activation of the electric pump increased the fuel pressure beyond the mechanical pump's ability to regulate, leading to an oversupply of fuel to the carburetor, a condition exacerbated by the use of carburetor heat.
- The high pressure also caused physical damage to the mechanical pump's flexible membrane, leading to fuel escaping through the vent.
- The primary cause was the installation of an electric pump by the aircraft manufacturer that did not comply with the engine manufacturer's installation manual regarding maximum allowable pressure.