What happened
On June 10, 2019, a private Flyer Pelican 500BR ultralight, registration CS-UUN, was performing a recreational flight from Tojeira aerodrome to Vendas Novas, Portugal. The flight was part of a special event celebrating the history of Portuguese aviation. After departing Vendas Novas for a return leg to Tojeira, the pilot encountered moderate turbulence and a 10-knot northwest wind.
During the cruise phase, the pilot utilized a technique of banking the aircraft into the wind to maintain the planned course. Approximately 20 minutes into the flight, the pilot observed that the fuel indicator for the right wing had dropped to zero, while the left wing indicator was approaching the red markings. Shortly thereafter, the engine began to lose power and eventually stopped completely.
At an altitude of 1,500 feet, the pilot declared an emergency and attempted an engine-out landing in a nearby field. However, due to difficulties managing energy during the emergency descent, the aircraft failed to lose sufficient altitude before striking the side barrier of the A12 motorway. The aircraft crossed two lanes of traffic at an estimated 70-degree angle, colliding with two vehicles traveling in a south-north direction and causing debris to strike a third vehicle. The pilot escaped without injury, though the passenger sustained minor injuries.
The investigation
The GPIAAF investigation focused on the fuel system and the circumstances leading to the engine failure. Investigators examined the aircraft's fuel tanks, which are integral to the wings and connected via a compensation tank. Tests revealed that due to a permanent deformation in the left landing gear, the aircraft naturally maintained a slight bank angle.
Further testing demonstrated that at a bank angle of only -3.5 degrees, the lower tank would cease to supply the engine once the fuel level reached 22 liters. The investigation also reviewed the aircraft's manuals, noting that they did not specify operational limitations regarding fuel levels beyond a standard 10-liter unusable amount.