What happened
On September 12, 2003, a Culver V, registration CS-ACY, departed from Coimbra Aerodrome at 15:53 UTC, intending to fly to Évora. The pilot had recently completed a 100-hour/annual inspection and initially intended to perform a proficiency flight before proceeding to his destination.
During the takeoff roll, the pilot noted that the aircraft required a longer runway than usual. Once airborne, despite applying maximum power, the pilot found unable to maintain a level flight altitude and observed a gradual loss of airspeed. The engine temperature also began to rise progressively. In an attempt to troubleshoot, the pilot cycled the landing gear, suspecting it might not have retracted fully, but the performance issues persisted.
Unable to return to Coimbra or reach the alternative airfield in Fátima due to the continuous loss of altitude, the pilot opted for an emergency landing on the A1 motorway at km 125.5. The aircraft landed successfully at 16:35 UTC in a section of the highway with low traffic. The pilot, who was the sole occupant, was uninjured, and there was no damage to the aircraft or third parties.
The investigation
The GPIAAF investigation examined the aircraft's performance capabilities and environmental conditions. The aircraft was powered by a Continental C-85-12FHJ engine. While the engine was within its operational hours, it had not undergone a mandatory overhaul based on its 57-year age.
Investigators performed performance calculations using the pilot's reported manifold pressure, RPM, and an outside air temperature (OAT) of approximately 40 ºC. The analysis determined that while the high temperature reduced available horsepower from 73 HP to approximately 68 HP, this reduction alone was insufficient to explain the inability to maintain level flight, as the aircraft could maintain cruise at much lower power settings.
Findings
- The aircraft possessed a weak power-to-weight ratio.
- High outside air temperatures (OAT) contributed to reduced engine performance.
- The pilot likely adopted a nose-high attitude in an attempt to prevent altitude loss, which increased aerodynamic drag and decreased airspeed.
- This high-drag attitude resulted in reduced airflow for engine cooling, further degrading engine performance and leading to the eventual loss of altitude.