What happened
On December 22, 1981, a Hughes 269C helicopter with registration CS-HAP, operated by Aeroavia Flight School, was conducting training maneuvers at Cascais Aerodrome in Portugal. The flight involved an instructor and a student pilot. After completing an instructional landing, the aircraft lifted off at low altitude to return to the apron, intending to conclude the morning's training session.
As the helicopter approached the transition between the apron and the runway, it experienced a sudden loss of power. Witnesses nearby reported hearing an abnormal noise just before impact. The student pilot distinctly felt a drop in rotor RPM. The aircraft struck the ground violently, causing the tail rotor to collide with the terrain. This collision destroyed the tail rotor assembly and resulted in a complete loss of directional control. The helicopter spun uncontrollably on the ground until it was destroyed. The incident occurred at 11:55 hours.
Both the instructor and the student exited the wreckage unharmed. They were promptly assisted by maintenance personnel on site. There were no injuries to the crew, and no damage was reported to third-party property or infrastructure.
The investigation
The GPIAAF investigated the circumstances surrounding the accident. The aircraft had been undergoing maintenance, and a report from the firm responsible for the engine overhaul revealed significant mechanical deficiencies. The inspection identified cracks in the spring plates of two cylinders, which allowed foreign objects to enter the compression chamber. Additionally, the distributor shaft exhibited cracks on its lobes, the connecting rods contained welds, and the crankshaft showed deep grooves at the bearing points.
The instructor held a valid Commercial Pilot License for helicopters and an instructor qualification, with approximately 2,300 hours of helicopter experience. The student pilot was undergoing standard training. Meteorological conditions were favorable, with light easterly winds and minimal cloud cover. No navigation aids or flight recorders were relevant to the investigation.
Findings
The investigation concluded that the aircraft suffered from critical engine deficiencies that likely caused a sudden loss of power. The mechanical failures within the engine prevented the rotor system from maintaining sufficient RPM during the low-altitude maneuver. This power loss, combined with the subsequent collision of the tail rotor with the ground, led to the total destruction of the helicopter.
The loss of power due to engine malfunction was the primary causal factor. The instructor was properly certified and qualified for the flight. The aircraft's structural failure was a direct result of the mechanical issues identified in the engine overhaul report.
Safety action
No specific safety recommendations or actions taken by the GPIAAF are recorded in this source material beyond the identification of the mechanical defects.