What happened
On 17 August 2017, an Airbus Helicopters EC120B Colibri, registration G-SWNG, was performing a private flight near Wellesbourne, Warwickshire. Following a period of routine maintenance, which included a compressor wash and an ‘A’ check, the pilot commenced the flight.
During the final stages of the landing approach, as the helicopter was performing a flare, the pilot heard an unusual noise. The pilot immediately landed the aircraft. Upon inspection, it was discovered that the right engine cowling had partially opened, with the forward latch assembly missing and the centre latch damaged. This movement caused the cowling to strike the inboard sections of all main rotor blades, resulting in damage to both the cowling and the blades. There were no injuries to the pilot.
The investigation
Investigators examined the aircraft's latching mechanism, which uses three hooked latches to secure the cowling to the helicopter structure. The examination of the remaining two latches showed no signs of unusual wear, distortion, or damage to the hooks, the helicopter structure, or the secondary spring locks.
An authorized maintenance organization confirmed that the contact between the cowling and the rotor blades was the direct cause of the blade damage. The investigation also noted that the inner faces of the latch levers had been painted in a contrasting colour to the airframe to provide a visual cue for identifying unlocked latches, a safety measure previously recommended by the manufacturer.
Findings
- The right engine cowling opened during the landing flare because the three cowling latches were left unlocked following maintenance.
- The pilot did not perform a pre-flight walkaround inspection, which would have likely revealed the unsecured latches.
- The completion of maintenance tasks immediately prior to the flight, combined with a short break away from the aircraft, likely caused a distraction that led to the omission of the inspection.