Introduction
On August 19, 2018, about 1320 Hawaiian standard time, a Eurocopter EC-130 B4 helicopter, registration N11QP, experienced an in-flight separation of its left-rear sliding door near Hilo, Hawaii. The helicopter sustained substantial damage to its main rotor blades. The pilot was not injured, and the passenger sustained minor injuries. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a maintenance flight.
Flight Details
The purpose of the flight, which originated from Hilo International Airport (ITO), was to perform track and balance procedures on the main rotor blades. Earlier that day, the pilot had conducted a previous flight but returned early due to issues with the track and balance equipment. Before the accident flight, the pilot performed a walk-around inspection, visually verifying that all doors, cowlings, and equipment were closed and secured. The pilot and the passenger, a maintenance apprentice seated in the right front seat, departed ITO about 1310.
Incident Description
After completing the maintenance checks and while en route back to ITO, the pilot lowered the collective to decelerate and began a slow descent. He then heard the left-rear sliding door suddenly slide open. Looking back, he saw the door off the helicopter in midair. Turning forward, he heard a loud noise and felt a jolt. The helicopter began to vibrate but remained controllable. The pilot initiated a precautionary landing onto a grass field. He indicated that the door appeared to have struck two main rotor blades and that he thought the door fell into the ocean.
The maintenance apprentice stated that, during the return flight, after leveling off from a descent, the door suddenly opened and separated from the helicopter. He noted that during takeoff for the previous flight, a maintenance technician had ensured the doors were closed correctly, but that did not occur before the accident flight.
Investigation Findings
The accident helicopter is equipped with a sliding rear door on the left side, which, when opened, is supported by a plastic latch on the fuselage at the end of the sliding door track. Examination of photographs and reports from the director of maintenance revealed that the helicopter’s left sliding door tracks and door latch assemblies were normal and unremarkable. The plastic latch on the fuselage was damaged, and a portion had separated from the fuselage. The sliding door itself was not recovered, preventing examination of the door and its locking components. A review of the helicopter's maintenance records found no previous door-related issues.
Subsequent Actions
On December 10, 2018, Airbus Helicopters published Alert Service Bulletin (ASB) ASB EC130-05A031 for operators of EC-130 B4 helicopters with sliding doors. The ASB made it mandatory to check the correct operation of the sliding door locking system by measuring the load required to unlock the sliding door, using a spring scale. The bulletin cited an in-flight opening and loss of a sliding door as the reason for its issuance.