What happened
On March 19, 1996, a HU-3 and00C helicopter, registration PT-HDM, operated by J. F. Aeroagrícola, was performing a takeoff from the unregistered São José Mill airfield in Igarassu, Pernambuco. Shortly after departing, at an altitude of approximately 200 feet, the pilot initiated a right-hand turn. During the maneuver, a loud bang and intense vibration were felt throughout the aircraft.
In an attempt to return to the runway, the pilot reversed the turn to the left. However, the aircraft lost altitude and the tail boom struck a perimeter fence. The helicopter subsequently lost control and struck the ground. Both the pilot and a passenger survived the impact without injuries, though the aircraft was a total loss.
The investigation
CENIPA's investigation revealed a critical chain of mechanical and operational failures. Post-accident analysis of the engine uncovered several discrepancies: a broken exhaust valve in cylinder number 1, misaligned piston rings in cylinders 3 and 4 causing compression loss, and oil leakage that fouled the spark plugs. Additionally, all spark plugs were found to be corroded and improperly calibrated.
Fuel samples also contained water, likely due to improper handling or storage. The investigation noted that the pilot was aware of excessive engine vibrations from previous flights but proceeded with the mission. Furthermore, the airfield's perimeter fence was found to be encroaching on the required runway safety zone, creating a significant obstacle.
Findings
- Deficient Maintenance: The engine had undergone service only 62 hours prior to the accident, yet significant mechanical defects remained unaddressed.
- Improper Emergency Procedure: Instead of executing an autorotation by lowering the collective to land in front of obstacles, the pilot attempted to return to the runway, which led to the tail strike.
- Operational Negligence: The pilot continued operations despite known excessive vibrations and the presence of water in the fuel, which could have been removed via proper pre-flight drainage.
- Inadequate Infrastructure: The unregistered airfield lacked proper clearance, with a perimeter fence located within the runway safety area.
- Lack of Oversight: The operator lacked a certified mechanic to support maintenance decisions and oversee fuel handling procedures.