What happened
On 26 July 2002, a Jetstream 41, registration G-MAJA, was being pushed back from Stand 12 at Dublin Airport for a scheduled public transport flight. As the pushback maneuver concluded, the ground crew—consisting of an engineer, a tug driver, and a training instructor—prepared to disconnect the towbar from the aircraft. The captain had already applied the aircraft's parking brake as instructed.
During the disconnection process, the engineer attempted to remove the towing pin from the tug lugs. However, as the tug driver engaged reverse gear, the pin accidentally slipped back into place. This sudden movement, combined with the aircraft's parking brake being engaged, created an intense mechanical force. The resulting jolt was felt by the passengers, and the aircraft's stall warning and unsafe gear systems were triggered. While there were no injuries among the 23 people on board, the aircraft sustained significant structural damage to the nose undercarriage and the lower skin.
The investigation
The investigation focused on the mechanical interaction between the tug, the towbar, and the aircraft's nose gear. Investigators examined the tug, which was a 25-ton vehicle, and found it was disproportionately powerful for the aircraft type. The towbar used featured a shock absorber designed to handle loads at least three times the weight of the Jetstream 41, making it effectively rigid and unable to cushion the impact for such a light aircraft.
Technical analysis revealed that when the pin re-engaged while the tug was in reverse, the shearpin on the towbar attachment head fractured. Because the towbar's design does not allow the head to separate from the bar, the tug continued to move until it hit a design stop, delivering an impulsive force directly to the nose gear. This force fractured the mounting for the down-lock roller and caused the roller to become embedded between the aircraft's forward pressure bulkhead and the lower skin.
Findings
- The primary cause of the damage was the inadvertent reinsertion of the towing pin at the exact moment the tug began moving in reverse.
- The tug used during the operation was too large and powerful for the specific aircraft being handled.
- The towbar's shock absorption capacity was incompatible with the light ramp weight of the Jetstream 41.
- The tight tolerances of the towing pin and lugs made the disconnection process difficult for the ground crew.
Safety action
Following the incident, the maintenance organization updated its pushback procedures to provide more specific instructions regarding towbar disconnection. Additionally, the organization began trials with a smaller, more appropriate tug to ensure better compatibility with turboprop aircraft operations.