Incident Overview
On Thursday, August 12, 2004, at 20:45 local time, a Bell 407 helicopter (registration EC-IMZ) operated by Helicópteros del Sureste, S.A. was engaged in aerial firefighting operations near Candasnos (Huesca), Spain. The helicopter had departed from the Peñalba Fire Base at 20:35 to assist in extinguishing a stubble and tire fire approximately four minutes away.
Sequence of Events
According to the pilot's statement, upon arrival at the fire zone, he conducted a reconnaissance lap and observed two power lines in the area. He landed near the fire, dropped off a forestry brigade, and installed a Bambi Bucket on the helicopter. He then took off to collect water from a nearby pond and proceeded to drop it on the fire. The water drop pass was made from south to north, parallel to one of the power lines, with the line to his right and the fire to his left.
After releasing the water, the pilot noticed a power line crossing perpendicularly ahead of the helicopter. He raised the nose to climb and clear the wires. As the helicopter was approximately over the line, he felt a tug from the rear and the nose dropped. He heard a minor impact but did not believe the main rotor was damaged. He stabilized the helicopter and landed without perceiving vibrations. The pilot did not release the Bambi Bucket via the cargo hook release controls.
Injuries and Damage
The pilot was uninjured. The helicopter sustained damage to one main rotor blade. The Bambi Bucket was rendered unusable. One tower of the power line was bent by the impact, but no cables were severed.
Pilot Information
The 33-year-old pilot held a commercial helicopter license with agroforestry rating limited to firefighting, valid until March 29, 2005, and type ratings for Bell 407 and HU 300. He had a valid medical certificate. In the previous 12 months, he had flown 67:45 hours; in the last 30 days, 18:45 hours; and in the last 24 hours, 1:45 hours.
Cargo Hook System
The cargo hook was mounted on the underside of the fuselage, with both electric and manual release. The electric release was activated by a switch on the cyclic control, protected by a circuit breaker. An emergency release lever operated independently of the electric switch.
Analysis
The water drop maneuver was conducted heading north, parallel to the south-north power line at a distance of about six meters. The line was to the pilot's right and the fire to his left. The Bambi Bucket was lower than the parallel power line during the discharge, limiting lateral escape options. The pilot did not release the bucket after the impact; releasing it could have prevented further damage and increased safety during landing.
Probable Cause
The incident occurred due to the impact of the Bambi Bucket suspended from the helicopter against cables, as a result of the pilot not noticing the presence of the power line in time.