History of Flight
On August 8, 2018, at about 0920 Hawaii time, a Hughes MD Helicopters Inc. 369D helicopter, registration N369MH, was substantially damaged during an accident near Honolulu, Hawaii. The commercial pilot sustained minor injuries, while the three passengers reported no injuries. The helicopter was operating as a Title 14 Code of Federal Regulations Part 136 revenue air tour flight.
The helicopter was the lead in a flight of two that departed Honolulu International Airport (HNL) at about 0909. The flight proceeded east/southeast along the shoreline. According to the pilot, while cruising at about 1,800 ft, he felt severe vibrations, heard a loud bang, and the helicopter began shaking violently. The pilot lowered the collective and entered a power-on autorotation, intending to land in a grassy clearing. He radioed his intentions to the trailing helicopter and informed his passengers. The pilot noted that small tail rotor pedal inputs significantly worsened the vibrations.
The pilot performed a partial run-on landing onto the clearing, about 13 miles east of HNL. On first contact, the helicopter bounced about 1 ft, and the subsequent slide across the dry, rocky grass field was rougher than expected. The helicopter came to a stop upright, and the pilot shut down the engine. The landing field was part of a public school grounds, and the pilot released the passengers to school staff while he inspected the helicopter and coordinated with his company.
Aircraft Information
The helicopter was equipped with a single 5-blade main rotor, a 4-blade tail rotor, and a T-configuration horizontal and vertical stabilizer. The accident helicopter had an aftermarket tail boom produced by Aerometals, approved under FAA supplemental type certificate STC SH5055NM. The tail rotor transmission attach hardware consisted of through-bolts and self-locking nut plates. The tail rotor assembly comprised two 2-blade assemblies mounted 90° apart on a four-arm fork, with teeter bearings and tension bolts.
The helicopter had accumulated about 14,419 total service hours. Its most recent 100-hour/annual inspection was completed on July 12, 2018, at 14,328 hours, and the most recent 300-hour inspection was on May 22, 2018, at 14,157 hours. The Aerometals tail boom was installed in May 2006, and a tail rotor transmission overhauled by California Aero Components was installed in August 2016. The accident fork assembly, containing improperly installed teeter bearings, was installed about 23 months before the accident.
Damage and Recovery
The helicopter came to rest upright on its landing skids, with the right skid fractured but still supporting the helicopter. Postaccident photographs showed multiple tail rotor blade and gearbox components were damaged. The helicopter was substantially damaged. Without NTSB or FAA knowledge or approval, and contrary to applicable regulations, the operator recovered the helicopter to its facility shortly after the accident and began disassembly for repair. More than a day later, the NTSB became aware and instructed the operator to cease repairs.