Airworthiness Directive after Two Fatal Bell 430 Accidents: Main Rotor – Pitch Link Clevis Fractures Angola and South Africa
Transport Canada has issued Airworthiness Directive (AD) CF-2021-26 to inspect the main rotor pitch link clevises and rod ends of the Bell 430. This followed two accidents that cost the lives of 11 people. The AD is considered an interim action and a further AD could follow. They explain:
In January 2021, a model 430 helicopter experienced an in-flight failure of a main rotor pitch link clevis resulting in loss of control of the helicopter and fatal injury to the five occupants on-board.
That accident occurred on 21 January 2021 to B430 ZT-RRT, operated by National Airways Corporation (NAC) as an air ambulance for Netcare 911, while en-route from Johannesburg to Pietermaritzburg in South Africa.
The Accident and Incident Investigations Division of the South African CAA has already published a preliminary report. That describes how approximately 1.5 hours into the flight and while cruising at 725 feet AGL, eyewitnesses report that “the helicopter suddenly started to spin around whilst losing height rapidly” and “saw what looked like helicopter parts breaking off before it crashed and burst into flames”. The wreckage was scattered over a 500 m radius. All 5 persons on board died.
The Transport Canada AD states that in that accident:
The main rotor pitch link clevis part number (P/N) 430-010-432-101 fractured at the exposed thread area above the nut and the fracture was consistent with fatigue damage.
Inspection of the failed part from the 2021 accident determined that the universal bearing P/N 212-010- 412-001 of the main rotor pitch link assembly was found with excessive wear and had increased resistance to rotation. Restriction in freedom of movement of the universal bearing can cause increased loads on the main rotor pitch link assembly and subsequent fatigue failure of the clevis prior to its life limit. The accident investigation is still ongoing.
They go on to reveal that:
A similar accident previously occurred in September 2016 on a model 430 helicopter where the main rotor pitch link clevis was found to have fractured at the neck area via fatigue damage that originated at a corrosion pit.
Transport Canada explain that:
This condition, if not corrected, could lead to crack initiation at the main rotor pitch link clevis neck or threaded area and consequent failure of the main rotor pitch link, resulting in loss of control of the helicopter. To address this unsafe condition, this AD requires an initial special detailed inspection (SDI) of the main rotor pitch link clevises and detailed visual inspection (DVI) of the universal bearings, and rectification, as required.
This AD also mandates a repetitive DVI of the main rotor pitch link clevises and universal bearings, and rectification, as required. Bell issued Alert Service Bulletin (ASB) 430-21-60 to provide instructions for inspection and replacement of the affected parts.
The Bell ASB states no reason for the inspection.
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Aerossurance‘s Andy Evans will be running two training sessions at European Rotors in November 2021. One will be on safety leadership and the other on how to procure and assure aviation services. He discussed these in a recent European Rotors Digital Series interview:
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