29th of September 2021, Blog #552

A 1991 built Britten Norman BN-2B-26 Islander was operating a scheduled domestic flight between Antigua and Montserrat, on board the aircraft besides the pilot, 6 passengers.

The severely damaged nose section of the aircraft (Source © Unknown)

The aircraft departed Antigua at 17.14 lt (local time), the following take-off and climb were uneventful as the aircraft reached its cruise altitude for the short 19-minute flight. The weather was good and visual meteorological conditions were present for the entire flight. The METAR for Montserrat gave the following weather details;

  • Wind - 060º at 5 knots

  • Clouds - 2/8 t0 3/8 Comulonimbus at 1600 feet

  • Temperature - 29ºC

When approaching Montserrat the Islander was the only aircraft operating in the area, the aircraft was positioned on a downwind leg for a visual approach to runway 10. The initial approach and approach to the runway were uneventful and a stable approach was flown at an approach speed 0f 65 knots, which was reduced to 60 knots as the aircraft touched down.

A smooth touchdown was made on the runway and before the aircraft was de-rotated the pilot applied the brakes. It became apparent to the pilot that the left brake felt "spongy" and seemed inefficient while the right brake felt normal. Due to the differential braking, the aircraft started to drift to the right two seconds after the touchdown. The pilot attempted to maintain directional control but was unable to do so. Five Seconds after touchdown the aircraft departed the paved runway. It continued on the grass adjacent to the runway until it hit an embankment and came to a stop.

As soon as the aircraft came to stop the pilot stopt both engines and vacated the aircraft through the flight deck door as the passengers evacuated through the right cabin exit, One passenger sustained minor injuries. The left main landing gear had failed resulting in the left cabin exit being unusable, as the landing gear was jammed against the door.

The failed left-hand main landing gear jammed the left-hand passenger door. (© AAIB)

The Air Accident Investigation Branch (AAIB) was alerted and an investigation was launched. As part of the investigation, the aircraft was inspected. Due to damage sustained in the accident, it was not possible to function test the pilot’s left brake system, but the pilot’s right brake system was found to operate normally. The left and right brake systems were visually inspected, and no leaks were apparent. Selected components from the left brake system were removed from the aircraft and shipped to the UK for more detailed inspection. A slight leak, caused by a flattened seal, was found on a calliper of the left outboard brake, this caused a reduced braking effect from the left brakes. The brake friction pads on the left outboard brake had been replaced the night before the accident. This process involved pushing the pistons back into the calliper to allow for the greater thickness of the new friction pads. Since the replacement, the aircraft had made six landings including one at Montserrat and two at Barbuda, which has a shorter runway than Montserrat, all without incident. There were no reported issues with the brakes for the first six flights after the friction pad replacement and the leak appears, therefore, to have developed after these flights. The leak was likely due to scoring of the piston bore and the flattened piston seal, both of which could not be identified unless the calliper was disassembled.

Aircraft track, white crosses CCTV data, yellow dots GPS data (© AAIB)

The investigation resulted in the following conclusion being presented by the AAIB;

"When the pilot applied the brakes on landing, a leak from one of the pistons of the left outboard brake calliper rendered the left brakes less effective than the right, causing the aircraft to veer to the right and depart the runway. Difficulty in maintaining directional control was compounded by the limited size of the runway and the use of an incorrect braking technique on landing.

The investigation also identified shortcomings with the operator’s manuals, procedures and regulatory oversight, these can be found in the investigation report (published on the 22nd of September 2022, which is accessible by clicking on the .pdf file below;

BN 2B Islander brake failure 29-sep-2021
Download PDF • 1.07MB

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