What happened
On August 17, 1992, at approximately 15:58 local time, a LAMA SA 315 helicopter, registration F-GIQB, was engaged in firefighting operations near Vila Cova de Perrinho, Vale de Cambra. The aircraft had departed from Albergaria-A-Velha to combat a forest fire in the region.
During the mission, the pilot attempted to refill the aircraft's water tank using a nearby irrigation reservoir to expedite the firefighting cycle. To facilitate this, the pilot performed a near-vertical descent into the reservoir area. During the process, the suction hose became entangled with the barbed wire atop the reservoir's perimeter fence. This entanglement caused the aircraft to become tethered, preventing it from maneuvering away from the site.
As the pilot attempted to compensate by adjusting the collective, the aircraft's tail swung downward and to the right, striking a rocky outcrop. This impact destroyed the tail rotor and resulted in a total loss of torque control. The pilot performed an immediate emergency landing on a pile of wood. The instability of the wood pile caused the aircraft to roll to the right upon impact, leading the main rotor blades to strike the ground. There were no fatalities, and the pilot escaped the wreckage uninjured.
The investigation
The GPIAAF investigation examined the wreckage, the site of the accident, and witness statements. Investigators analyzed the structural damage to the F-GIQB, noting that the main and tail rotors were destroyed and the fuselage sustained significant deformation. The investigation also reviewed the environmental conditions, noting that while the weather was good, winds were blowing from the valley with varying intensity and direction. The investigation confirmed that the aircraft held a valid Certificate of Airworthiness and the pilot was properly certified for the operation.
Findings
- The primary cause of the accident was the entanglement of the suction hose and terminal with the barbed wire on the reservoir fence.
- The reservoir location was unsuitable for the operation due to natural obstacles, including steep slopes, trees, and rocky outcrops, as well as man-made obstacles like a telephone line and utility poles.
- The impact with the rocky outcrop led to the destruction of the tail rotor and subsequent loss of directional control.
- The emergency landing on an unstable pile of wood caused the aircraft to roll and the main rotor to strike the ground.