What happened
On August 19, 2018, at approximately 1320 Hawaiian standard time, a Eurocopter EC1t30 B4 helicopter, registration N11QP, was involved in an accident near Hilo, Hawaii. The flight, operated by Blue Hawaiian Helicopters, was being conducted under 14 CFR Part 91 for the purpose of performing main rotor blade track and balance maintenance.
The flight departed from Hilo International Airport (ITO) with the pilot and a maintenance apprentice on board. While en route back to the airport, the pilot lowered the collective to decelerate and began a slow descent. During this phase, the left-rear sliding door suddenly slid open and separated from the aircraft. The pilot observed the door in midair before hearing a loud noise and feeling a jolt. The door struck two of the three main rotor blades, causing the helicopter to vibrate. The pilot was able to maintain control and performed a precautionary landing in a grass field. The passenger sustained one minor injury, and the pilot was not injured.
The investigation
Investigators found that the helicopter's left sliding door tracks and door latch assemblies were in normal condition. However, the plastic latch on the fuselage, which supports the door when it is in the open position, was damaged, and a portion of it had separated from the fuselage. The sliding door itself was not recovered because it fell into the ocean, which prevented a full examination of the door and its locking mechanisms.
Maintenance records for N11QP showed no prior issues regarding the doors. Following the accident, Airbus Helicopters issued Alert Service Bulletin ASB EC130-05A031. This bulletin made it mandatory for operators of EC-130 B4 helicopters to use a spring scale to measure the load required to unlock the sliding door to ensure the locking system was operating correctly.