Incident Description
On 26 November 2005 at 1020 UTC, a Boeing 737-8AS (registration EI-DAP) was parked on Stand 4 at Glasgow Prestwick Airport after a passenger flight. The flight crew had initiated normal shutdown procedures when a baggage belt vehicle approached the front cargo hold. As the driver applied the footbrake, the pedal travelled to the floor without slowing the vehicle. The driver attempted to engage the handbrake but failed, and steered right to avoid the open hold. The conveyor belt, which overhangs the front of the vehicle, struck the aircraft fuselage, bringing the vehicle to a stop. The captain felt the impact and later reported not immediately knowing its significance due to delayed communication from ground crew. He opened the flight deck window and was told the belt had hit the fuselage, after which he decided to disembark passengers via rear stairs. No one was injured.
Emergency Response
Shortly after the collision, ground crew contacted their line manager, who arrived and telephoned the Motor Transport department. At about 1040 hrs, approximately 20 minutes later, a ground operator with mobile patrol duties notified ATC. An 'Aircraft Ground Incident' was declared, and fire services arrived shortly thereafter.
Airfield Investigation
The Airfield Operations Manager conducted a comprehensive investigation, including interviews and an independent vehicle inspection. The vehicle was an Avia Lift APL 900 Mk1 (built 1982), self-propelled with a cab on the left and a conveyor belt overhanging the front on the right. Its footbrake operated a non-assisted single circuit hydraulic system to drum brakes; the parking brake was hand-operated. Automatic transmission included a park setting.
Vehicle Maintenance
Service records showed the vehicle had received six-month services in June 2005 and September 2004, each with 63 maintenance actions. The airport authority maintained the vehicle; inspections were not independent but had signatures of a maintainer and supervisor. The inspections aligned with the 30-point safety check recommended in CAP 642, though CAP 642 is not mandatory. The CAA expects airport operators to adopt CAP 642 guidance as part of their Safety Management Systems (SMS) per CAP 168.
Vehicle Inspection
Post-incident inspection by an independent organisation revealed:
- Footbrake system: The brake pedal could be pushed through full travel without resistance. The hydraulic pipe to the front offside wheel brake cylinder was fractured, causing immediate loss of brake fluid pressure. The driver would have had no prior warning. The fracture cause was not determined.
- Parking brake: The front section of the parking brake cable, replaced in June 2005, was seized, rendering parking and emergency braking unavailable. This defect would have been noticeable during a daily check. The downstream system operated satisfactorily.
- Use of park with automatic transmission: Regular use of the park setting could have reduced parking brake usage, possibly contributing to cable seizure and decreased detection probability.
Analysis
The incident was caused by a failure in the hydraulic brake pipe. The vehicle had been serviced twice in the prior 14 months, and brake pipe parts had been replaced 12 and 14 months before the incident. However, the vehicle became unsafe within six months of its last service. The impending brake pipe failure and defective parking brake might have been detected with a daily check or quarterly service and an effective defect reporting system.
Safety Actions
Airfield management recommended a full review of the ground vehicle fleet, defect reporting, maintenance reporting, servicing schedule content and frequency, and Motor Transport manning levels. They also recommended improving awareness of prompt emergency procedures, including immediate ground incident reporting to the aircraft captain.
Safety Recommendation
The AAIB issued Safety Recommendation 2006-060: The Civil Aviation Authority should remind airport operators that their SMS should ensure safe maintenance and use standards for all vehicles and mobile equipment operating near aircraft.