History of Flight
On June 8, 2022, about 1726 Hawaii-Aleutian standard time, a Bell 407 helicopter, registration N402SH, sustained substantial damage when it impacted a lava field near Kalea, Hawaii. The pilot and two passengers sustained serious injuries; three passengers sustained minor injuries. The helicopter was operated by Paradise Helicopters as a Title 14 Code of Federal Regulations Part 135 on-demand air tour flight.
The helicopter departed the company base at Ellison Onizuka Kona International Airport (PHKO) about 1701, traveling south for an air tour. Automatic dependent surveillance-broadcast and company flight track data showed the helicopter proceeded southeast toward the South Point area. The pilot reported a normal first part of the flight. About 35 minutes after departure, at 1,500 ft agl and 130 knots, the helicopter experienced a violent upset followed by an uncontrolled right yaw. A passenger in the aft-left forward-facing seat observed an object fall from the helicopter but could not identify it. The pilot made two mayday calls and attempted recovery as the helicopter spun and descended rapidly. It subsequently impacted a lava field and came to rest on its left side.
A passenger placed an emergency call at about 1728. Simultaneously, the US Coast Guard Honolulu Joint Rescue Coordination Center received an emergency locator transmitter alert and initiated search and rescue operations.
Aircraft Information
Airframe Structure
The helicopter fuselage comprised three primary structural assemblies: forward fuselage, intermediate fuselage, and tail boom. The intermediate fuselage extends from the rear of the passenger compartment to the front of the tail boom; its aft portion is called the aft fuselage. Four aft fuselage longerons (upper-left, upper-right, lower-left, lower-right) attach to the aft fuselage bulkhead. The tail boom attaches to the intermediate fuselage via fasteners connecting the four aft fuselage longerons to four corresponding longerons at the forward end of the tail boom. According to Bell, tail rotor thrust produces tension on the left attachment points and compression on the right; weight and aerodynamic forces add tension on the upper and compression on the lower points. The upper-left attachment point experiences the highest tension load.
Maintenance Records
The most recent 300-hour torque check of the tail boom attachment fasteners was completed on May 4, 2022, at 22,891.4 flight hours. On June 6, 2022, the helicopter had 23,005.6 flight hours (114.2 since the torque check) and 30,490 total flight cycles. No additional maintenance was performed on the attachment fasteners after the torque check.
The tail boom (part number 407-030-801-205D, serial number BP-1598) was installed on August 23, 2009, at 5,780.0 flight hours. It was last removed and reinstalled on July 3, 2014, for longeron and frame repairs. The work order indicated that a repair station assisted the operator in accomplishing Bell TB 407-12-96 Revision A, which covered installation of a redesigned aft fuselage upper-left longeron assembly.
Technical Bulletins
Bell TB 407-07-78 (September 19, 2007) introduced an improved machined aft fuselage bulkhead (P/N 407-030-027-101), which was installed on the accident helicopter. A later revision (TB 407-07-78 Rev A, August 2020) introduced a reinforced inside flange in the upper left area. The helicopter records contained no entries regarding TB 407-07-78 or TB 407-12-96.
Both TBs utilize an aluminum drill plate to verify alignment of the four tail boom attachment fittings and bolt holes. TB 407-12-96 Rev A recommends installation of the new bulkhead per TB 407-07-78 before final installation of the upper-left longeron and bulkhead. The TBs include detailed procedures for installing the bulkhead using existing or new pilot holes, and for verifying planarity within 0.002 inches.
Wreckage and Impact Information
NTSB examination revealed the tail boom came to rest about 762 ft northeast of the main wreckage (fuselage, engine, main rotor system). The tail boom separated at the tail boom attach point. The upper-left attachment fitting fastener was missing; the lower-left attachment fitting was fractured with fatigue signatures. Fasteners for the lower-left, lower-right, and upper-right fittings were present.
Postaccident examination of the rotor system, flight control system, and engine found no pre-impact malfunctions or failures. Detailed examination of the attachment structure showed significant deformation. The upper-right, lower-left, and lower-right attachment hardware assemblies were consistent with maintenance manual requirements; no corrosion preventative compound (CPC) was on exposed threads. Torque measurements for the upper-right and lower-right assemblies exceeded the lower limit.
The lower-left fitting fracture exhibited fatigue cracking from two origins (O1 and O2). Fatigue crack O1 emanated from multiple origins at the outer surface near the inner transition radius; it propagated about 1 inch with alternating fatigue and overstress features. Fatigue crack O2 emanated from a corrosion pit and measured about 0.75 inch. The upper-right and lower-right fittings showed overstress fracture. The upper-left bolt hole in the fuselage frame contained circumferential gouge and impression marks, more severe on one side; other bolt holes showed no such damage.
Attachment bolts were NAS627 specification. Hardness testing of the upper-right and lower-left bolts was within the specified 39–43 HRC range; the lower-right bolt measured 44 HRC, exceeding the upper limit. Material grade, grip length, and diameter complied with specifications.
Additional Information
On December 1, 2022, based on the investigation findings, the NTSB issued four urgent safety recommendations (A-22-28 through -31) to the FAA and Transport Canada.