What happened
On 28 May 2012, a Jetstream 4100, registration G-MAJJ, was undergoing pushback from a stand at Brussels National Airport. During the maneuver, the aircraft experienced a sudden, abrupt halt that caused the shear pin on the towbar to break. The pilot, after consulting with the ground agent and noting no visible external damage or steering issues, elected to continue the flight.
Following the pushback, the aircraft completed several sectors. During subsequent flights on 29 May, multiple crews reported unusual sensations, including a "clunking" sound and a feeling of metal stretching or crushing beneath the cockpit floor during climbs. Despite these symptoms being noted, the aircraft continued operations until landing at Aberdeen Airport, where a maintenance inspection eventually revealed significant structural damage.
The investigation
Investigators examined airport CCTV footage, flight data recorder (FDR) analysis, and witness statements. The footage confirmed the aircraft experienced a sharp jolt during the initial pushback in Brussels. Analysis of the FDR ruled out heavy landings or brake applications as the cause of the damage.
Technical analysis of the equipment revealed that the pushback tractor used weighed approximately 14,000 kg, significantly exceeding the 4,500 kg maximum recommended by the aircraft maintenance manual. This excess mass provided enough momentum to apply a massive longitudinal force to the aircraft when the pivot bolt reached the end of its slot, leading to the shear pin failure.
Findings
- The primary cause of the structural damage was the excessive longitudinal force applied to the aircraft during pushback, facilitated by the use of a tug far heavier than the manufacturer's recommendation.
- The damage, which included the rear pressure bulkhead of the nose landing gear bay, the lower fuselage skin, and the keel plate, went undetected for eight flight sectors.
- Identification of the damage was hindered by its location at the bottom of the fuselage, which is difficult to inspect from a standing position, especially in low-light conditions.
- A breakdown in defect reporting meant that while crews experienced physical symptoms of the damage, these were not effectively escalated to trigger a mandatory inspection.