The information is contained in a note issued by the Office for the Prevention and Investigation of Accidents with Aircraft and Rail Accidents (GPIAAF), which Lusa has seen.

The Eurocopter took off at 3.10 p.m. from a private aerodrome at Valongo, in Porto district, with a team of five firefighters on board and fire-fighting equipment consisting of a basket and bucket. After dropping the team on the ground, and lowering the bucket into position, the pilot flew the helicopter to a nearby water source to fill up for the first time with a view to emptying the water onto the fire.

As the note states, "after the cycle was repeated, on the second approach to the site of the fire and in coordination with another aircraft" that was operating in the area, "the pilot, knowing of the existence and location of the aerial power cables that existed in the location, defines the trajectory for the second drop.

"After crossing a first very-high-voltage line, duly indicated and composed of 14 conductors, the bucket suspended from the aircraft collided with the cables of the second line positioned at lower down and about 45 metres horizontally from the first, which is why it was not marked," the GPIAAF states.

The section in question of the second line, according to the note, "is characterised by a span of 400 meters” between two poles to the east and west.

"With the tail rotor destroyed, the vibrations induced by this lead to a rapid separation of the vertical stabiliser [that is] typical in these events of severe rotor 'unbalancing',” the note continues. “Now without its tail rotor and without vertical stabiliser the aircraft starts to rotate counterclockwise as an effect of the torque of the main rotor.

“The loss of control of the aircraft was inevitable and [resulted in the] consequent abrupt drop in rotation, traversing 66 meters until it came to a stop", the GPIAAF says.

The resulting "violent” crash on the ground immediately triggered an “intense” fire that “fully consumed the aircraft", the note states, adding that "in this process the pilot, the sole occupant of the aircraft was fatally injured".

Ferreira, 36, was a pilot in the Portuguese Air Force’s 751 squadron and also commander of the volunteer firefighters of Cete, in Paredes, in Porto district.