What happened
On April 16, 2005, at approximately 09:10 UTC, a Campana AN-4 ultralight, registration CS-UHM, departed from the Palma airfield for a recreational flight to Évora Airport. While cruising at 2,000 feet over the S. Cristóvão area in Montemor-o-Novo, the aircraft's engine suddenly stopped.
The pilot immediately contacted Lisbon Flight Information Service (FIS) to declare an emergency and notify controllers of the need for an emergency landing. Air Traffic Control activated search and rescue procedures. The pilot successfully performed an emergency landing on a reasonably flat, unprepared field. Following the landing, the pilot contacted controllers to confirm that there were no injuries and no damage to the aircraft, prompting the cancellation of the rescue mission.
The investigation
The GPIAAF investigation focused on the circumstances leading to the engine failure. The pilot, who held a valid ultralight pilot license and significant experience in this specific aircraft, conducted a post-landing inspection to identify the cause of the power loss. The investigation established that the pilot's documentation and medical certification were both valid at the time of the occurrence.
Findings
The investigation determined that the engine failure was caused by an alteration in the air-fuel mixture within the engine intake. This was specifically due to the degradation of the fuel supply line structure, which had developed cracks. These cracks allowed air to enter the fuel system, disrupting the proper combustion process. The pilot was able to replace the faulty tubing on-site, after which the aircraft was able to depart from the landing site and return to the original airfield without further incident.