What happened
On March 15, 2012, a Piper PA-28RT-201, registration I-PITU, was conducting a visual flight rules (VFR) flight from Torino Aeritalia to Aosta. The aircraft was operated by Aero Club di Torino and carried a single pilot. During the flight, the engine suddenly shut down, prompting the pilot to declare an emergency to the Milan Flight Information Center (FIC). Unable to continue the flight, the pilot performed an emergency landing in an uncultable field near the Montalto Dora aerodrome. There were no injuries to the pilot and no damage to the aircraft or surrounding property.
The investigation
The ANSV investigation focused on the cause of the engine failure and the maintenance history of the aircraft. The investigation revealed that the aircraft had undergone engine maintenance approximately 12 hours prior to the incident, which included the removal, reconstruction, and reinstallation of flexible fuel lines. While the maintenance records documented the disassembly and rework of these lines, they failed to record the reinstallation process.
Upon inspecting the aircraft at the landing site, investigators discovered a fuel leak at the connection of a flexible fuel line on the fuel flow divider. An analysis of the connector (P/N 526-4) showed that the torque applied during installation was insufficient. This was evidenced by a visual reference mark on the nut, which indicated that the nut had been improperly seated. Further technical review of the Lycoming engine overhaul manual revealed that the required torque values for this specific part were listed in a table for non-flexible metal lines rather than the table designated for flexible lines, creating potential for error during maintenance.
Findings
- The engine shutdown was caused by a loss of pressure in the fuel injector system.
- The fuel leak originated from a connector (P/N 526-4) that had not been tightened to the correct torque.
- The maintenance documentation failed to record the reinstallation of the fuel lines.
- The engine maintenance manual contained confusing instructions, as the necessary torque specifications for the flexible lines were located in a different table intended for rigid metal lines.