Bell 407 N501PH

Summary

On 8 June 2015 at about 19:32 local time, a Bell 407 registered N501PH, operated by PHI Inc, was involved in an accident near Pecan Island, Louisiana, United States. 5 people were on board and nobody was injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

8 June 2015 at 19:32

Classification

Accident

Location

Pecan Island, Louisiana, United States

Coordinates

29.6178, -92.3533

Aircraft

Bell 407

Registration

N501PH

Category

Helicopter

Year built

1999

Engines

1

Operator

PHI Inc

Operating rule

Part 135: Air Taxi & Commuter

Phase of flight

Not recorded

Route

Vermilion Block → Pecan Island

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

CEN15LA265

Nobody was injured.

The fatigue fracture of the tail rotor gearbox attachment studs, which resulted in a loss of tail rotor control and a subsequent hard landing.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

The operator reported that the helicopter air taxi flight was in cruise about 1,000 ft above ground level when the pilot felt an impact and a strong vibration. The pilot completed an instrument and functional control check and could not immediately identify any anomalies. The pilot stated that, as he slowed the helicopter for landing, he noticed a "heavy mechanical sound and strong vibration." The vibration worsened, and the pilot began to have difficulty controlling the helicopter; he subsequently initiated an autorotation and deployed the helicopter's floats. The helicopter touched down in a marshy area, and the pilot and passengers egressed. During the landing, the main rotor blades contacted the tail boom and one of the tail rotor blades, resulting in separation of the tail rotor gearbox (TRGB) support structure, which was subsequently located in the marsh. A postaccident examination and metallurgical analysis revealed that fatigue fractures on two of the four TRGB attachment studs likely existed before the accident flight. As the fatigue fractures grew larger through the first two attachment studs, their load-carrying capability lessened, and the additional load was transferred to the remaining attachment studs. The progressive failure of the fatigued TRGB attachment studs led to the vibrations felt by the pilot and, ultimately, the uncommanded right yaw and subsequent loss of tail rotor control. The reverse- bending, high-cycle fatigue fracture initiation mode observed on two of the TRGB studs suggests the fatigue fractures were a result of a loss of torque of the attachment stud nuts. The reason for the loss of torque could not be determined based on the available information.

Quoted verbatim from the NTSB record.