Mail plane’s rudder problem could have been avoided

The issue was found to be corrosion to steel bearings, which manufacturer ATR had recommended be replaced with stainless steel bearings in 1993, but the work was not done.

G-NPTF has been leased to West Atlantic since 2022 and regularly flies the mail between Guernsey and East Midlands.

The UK Air Accident Investigation Branch examined an incident at Belfast Airport in March 2023.

The plane had been in Guernsey for three days, before flying to East Midlands safely. Issues arose when the plane flew to Belfast the next day.

Pre-flight checks found that the stiff rudder could only be moved with significant effort, but the pilots decided to continue with the flight.

As the plane came into land there was a light wind, so the co-pilot tried to use the rudder to stop the plane drifting.

But he found the rudder pedals almost impossible to move. Realising there was a problem, the commander immediately took control and placed the aircraft on the ground at Belfast Airport, rapidly de-rotating the nosewheel to allow him to use the nosewheel steering.

The plane was unloaded and taken to a remote stand. There, it was found that the rudder pedals would not move at all.

Initial checks failed to find the problem, so the plane was taken into a hangar for a detailed check.

The AAIB said this found that the problem was caused by the rear quadrant support bearings. One was found to completely seized up and the other was rough when rotated.

‘Both bearings showed evidence of corrosive attack,’ the report said.

‘The degradation of the bearings would have substantially reduced or prevented their ability to rotate freely, and thus resisted the movement of the rear quadrant shaft, which would have resulted in the difficulties reported in the rudder operation.’

G-NPTF was built in 1990 and was converted into a cargo plane in 2014.

It was the oldest plane in the West Atlantic fleet when the incident happened.

There had been three separate reports of rudder stiffness made in February 2023, a month before the incident. The plane was then grounded for 10 days in Guernsey to troubleshoot the problem.

Various operational tests were performed and equipment replaced.

ATR was contacted for help and various tests were suggested, but the rudder rear quadrant shaft and its support bearings were not specifically mentioned.

A maintenance engineer reported that the rudder could be moved by hand and that the rudder pedals had no resistance, and it returned to service.

The rear quadrant shaft support bearings on the plane were made of steel. It was recommended in 1993 that the bearings be replaced with cadmium-plated, corrosion-resistant, stainless steel bearings, due to reports of seized flight control bearings due to corrosion – but this was optional. Only six planes were reported to have been updated and G-NPTF was not one of them.

Following the incident, G-NPTF’s rear quadrant shaft and bearings were replaced.

ATR has said that in-service reports of problems with the rudder rear quadrant shaft support bearings were extremely rare.

In the wake of this incident, ATR has launched a review of inspections of its rudder mechanical controls.