What aircraft was involved and where did it happen?

The accident on null involved a aircraft, registration EI-REI, at IE.

What was the probable cause of the accident?

Corrosion on the threaded area of the torque link apex pin likely caused the retaining nut and locking washer to separate, allowing the pin to fall out.

Corrosion suspected in nose gear component loss on ATR 72

A severe nose wheel shimmy during landing at Dublin Airport led to the discovery of a missing torque link apex pin on an ATR 72-201.

What happened

On 30 March 2013, an ATR 72-201, registration EI-REI, was performing a scheduled passenger flight from Edinburgh to Dublin. The aircraft was carrying 57 passengers and 4 crew members. While the landing on Runway 10 was initially routine, the flight crew experienced a violent nose wheel shimmy as the aircraft slowed below 40 knots.

The aircraft was brought to a stop on the runway, and the Airport Fire Service attended the scene. While there were no injuries and only minor damage to the aircraft, a subsequent inspection of the nose landing gear revealed that the torque link apex pin assembly, including the retaining nut and washers, had completely detached and was missing. The loss of the upper link caused damage to the weight-on-wheel switch assembly and the inner side of both nose wheels.

The investigation

The AAIU investigation focused on the mechanical integrity of the nose landing gear and the maintenance history of the aircraft. Investigators were unable to recover the missing pin or hardware from the runway or the departure airport.

During the inquiry, the operator identified that at certain outstations, the use of large wheel chocks could potentially lodge under the apex pin's locking washer, potentially displacing it during chock removal. Furthermore, a fleet-wide inspection by the operator revealed that several other apex pins in their ATR fleet exhibited varying degrees of corrosion, specifically where the cadmium protection had degraded.

Findings

The primary cause of the incident was likely corrosion on the threaded portion of the apex pin, which caused the serrated washer and retaining nut to separate, allowing the pin to migrate free.
The degradation of the cadmium protection on the pin threads made the component susceptible to this corrosion.
The loss of the pin was a contributing factor to the severe shimmy experienced during the landing roll.
The operator has since implemented a new maintenance task to inspect these pins every four years and issued ground crew instructions regarding the careful placement of wheel chocks.