What happened
On the afternoon of August 23, 1998, a Cessna 152, registration CS-AUS, operated by Aeroclube do Porto, departed Vilar de Luz aerodrome for a scheduled forest fire reconnaissance and surveillance mission. The flight was part of a protocol between local flying clubs and the Ministry of Internal Administration.
Approximately 80 minutes into the flight, while flying at 3,0 and over the Valongo area, the engine began to sputter before failing completely. Due to heavy smoke from nearby wildfires and late-afternoon haze, horizontal visibility was significantly reduced. The pilot determined that returning to Vilar de Luz was not feasible and instead selected an open cornfield near Nossa Senhora da Paz, Alfena, for an emergency landing.
While the pilot successfully executed the forced landing, the aircraft's nose gear collapsed upon impact. The momentum caused the aircraft to rotate around its wing axis, ultimately coming to rest in an inverted position. The pilot escaped the wreckage uninjured, though the aircraft sustained severe damage, including a fractured engine mount and nose gear.
The investigation
The GPIAAF investigation focused on the fuel state of the aircraft and the pilot's pre-flight procedures. Investigators examined the aircraft's fuel system and found no evidence of leaks or fuel spills at the crash site. They also noted that the aircraft's fuel quantity indicators were known to be unreliable, a fact the pilot was aware of.
To verify fuel levels, the pilot had used a manual method, inserting a finger into the fuel tanks to estimate the quantity. The investigation calculated that based on the aircraft's consumption rate and the last recorded refueling on August 22, the aircraft likely had significantly less fuel than the pilot had estimated. Furthermore, the investigation found that the tanks had not been topped off during the previous refueling, which contradicted manufacturer recommendations to prevent water contamination.
Findings
- The primary cause of the accident was deficient flight planning by the pilot, which led to an engine failure due to fuel exhaustion.
- The pilot failed to follow the established checklist procedures to unequivocally verify the total fuel quantity on board.
- Incomplete operational procedures during pre-flight inspections prevented an accurate real-time determination of the fuel available for the planned mission.
- The emergency landing was complicated by the terrain, which contributed to the aircraft capsizing after the initial impact.
Safety action
- Pilots should strictly adhere to all operational procedures outlined in the approved Flight Manual, particularly during the flight planning phase, to ensure all mission requirements can be safely met.