What happened
On November 10, 2007, at approximately 14:00 UTC, a Eurocopter AS 350 B3, registration CS-HMG, was engaged in firefighting operations near Melgaço, Portugal. The aircraft, operated by Empresa de Meios Aéreos, S.A. (EMA), was responding to a forest fire in the Serra da Peneda mountains. After refilling its Bambi Bucket at a nearby water source, the helicopter returned to the fire site to execute a water drop.
As the pilot attempted a left turn to position the aircraft for a south-to-north water release, the aircraft encountered significant difficulties. During the maneuver, the Bambi Bucket began to oscillate violently, inducing a pendulum effect. This caused the helicopter to lose control and enter a left-hand rotation, ultimately resulting in a high-impact collision with the terrain on a steep, 60-degree slope. The impact caused the aircraft to disintegrate and catch fire. The pilot, the sole occupant, was killed in the accident.
The investigation
The GPIAAF investigation examined the aircraft's maintenance records, the pilot's training history, and the operational procedures of the operator. The investigation focused on the flight dynamics during the heavy-load maneuver, the meteorological conditions at the time of the accident, and the accuracy of the aircraft's weight and balance calculations. Investigators also reviewed the pilot's experience in mountain flying and specialized firefighting maneuvers.
Findings
- The primary cause of the accident was inadequate flight technique during a tight turn while carrying a heavy external load, which triggered a pendulum motion in the Bambi Bucket and led to a loss of control.
- The pilot lacked specific training in mountain flying and had limited experience in specialized firefighting missions and heavy-load external sling operations.
- Environmental factors, including moderate winds and downdrafts caused by the terrain (mountain effect), contributed to the instability of the aircraft.
- The aircraft's weight and balance calculation sheet contained errors, specifically regarding the maximum capacity of the bucket for certain configurations, which could lead to incorrect mass calculations.
- The operator's organization was found to be deficient, as it failed to identify the need for mountain flight training and did not provide sufficient dual-command training for real-world firefighting missions.
- The pilot did not execute emergency procedures, such as releasing the water bucket, during the loss-of-control event.
Safety action
- The operator was recommended to revise its weight and balance calculation sheets for the AS 350 B3 fleet to ensure correct bucket capacity values are used.
- It was recommended that the operator implement practical mountain flight training for pilots operating above 1,000 meters.
- The investigation recommended that the operator include dual-command missions in the training syllabus for pilots new to firefighting.
- The national aviation authority (INAC) was advised to review aeronautical information circulars regarding minimum training requirements for aircraft engaged in forest fire operations.