What happened
On June 22, 2019, an Alpi Pioneer 200 ultralight aircraft, registered CS-UNF, was performing a recreational flight near Chamusca, Portugal. The pilot had been participating in a military simulation exercise, using the aircraft for aerial observation. After completing several local flights throughout the day, the pilot departed from Santa Margarida at 15:55 UTC, heading toward the base at Lezírias.
Approximately ten minutes into the flight, at an altitude of roughly 1,000 feet, the engine stopped. After an unsuccessful attempt to restart the engine, the pilot performed an emergency landing in agricultural fields. The pilot initially considered landing on an access road but aborted the maneuver due to the presence of a power line. The aircraft sustained substantial damage to the landing gear, the first structural bulkhead, and the firewall, leading to the loss of its flight certificate. The pilot escaped the crash uninjured.
The investigation
The GPIAAF investigation examined the aircraft's fuel system and maintenance history. The investigation revealed that the aircraft had undergone significant, undocumented modifications to its fuel system. Specifically, an auxiliary tank had been added, along with a shut-off valve between tanks and a reconfiguration of the electric pump from a parallel to a series installation. These changes were not documented in the aircraft's manual or cockpit labels, leaving the pilot unaware of the correct system sequencing.
Furthermore, the investigation found that the fuel indicator display contained overlapping, manual markings, and the manual dipstick was inaccurate in the lower half of its scale. During the post-accident assessment, investigators found a significant amount of solid debris in the fuel filter and drain ports.
Findings
- The primary cause of the engine failure was a blockage in the fuel supply line to the auxiliary tank, caused by sediment accumulation in the main tank collector area.
- The pilot's manual fuel gauge reading of 40 liters before the final flight was inaccurate, as the auxiliary tank was already empty at that time.
- Significant, unapproved modifications to the fuel system increased operational complexity and risk.
- The fuel indicator and manual dipstick provided unreliable measurements.
- The pilot had limited experience specifically with this aircraft type, having built up intensive flight activity only within the previous seven months.