History of the Flight
The Bell 206B helicopter was being used to transport fuel barrels via sling from a beach to a tent camp. After delivering several barrels, the pilot flew two barrels to the camp generator shed. As the helicopter approached the shed, the pilot transitioned to a hover and began a vertical descent to place the barrels on the ground. When the barrels were approximately two feet above the ground, the helicopter departed from controlled flight and rotated rapidly to the right through three full rotations. A ground assistant who had positioned himself under the helicopter to stabilize the barrels ran clear. The helicopter then struck the ground upright and rolled onto its right side.
Injuries and Damage
The pilot sustained minor injuries. The ground assistant was uninjured. The helicopter was substantially damaged: the skid cross tubes detached from the fuselage, and the main rotor struck and severed the tail boom. The cockpit and cabin remained intact.
Aircraft and Pilot Information
The helicopter was a Bell 206B JetRanger III, serial number 3231, manufactured in 1981. It was powered by a single Allison 250-C20B engine. Total airframe time was 10,407 hours. The aft short tail rotor drive shaft had accumulated approximately 19,000 hours of service, most in a corrosive saltwater environment after previous service in the Arabian Gulf. The pilot, aged 32, held a Commercial Pilot Licence and had 2,300 total flying hours, including 2,000 hours on type. He was qualified on the Bell 206B.
Causal Factors
The investigation determined that the aft short tail rotor drive shaft failed in an area weakened by intergranular cracking. This cracking initiated from corrosive attack on the interior wall of the shaft. The drive shaft failure resulted in a loss of tail rotor thrust. The failure occurred while the helicopter was hovering at an altitude that precluded a successful autorotation. The corrosion was not visible externally, and no scheduled internal inspection existed. The shaft had been improperly reworked at some point, which likely scratched the interior protective coating and allowed corrosion to initiate.
Additional Findings
The pilot did not release the sling load to avoid dropping it on the ground assistant. The pilot was not wearing the available shoulder harness. It is probable that the use of a protective helmet prevented serious head injury.