What happened
On July 24, 2006, a Boeing 737-700, registration PH-XRE, was parked at Stand 3 of Pisa Airport during baggage unloading operations. While approaching the aircraft's forward cargo hold, a motorized baggage belt operated by the airport management company, SAT, struck the lower cowling of the aircraft's right engine. There were no injuries to the flight crew or the ground personnel involved, though the aircraft sustained damage to the engine cowling.
The investigation
The ANSV investigation focused on the mechanical failure of the baggage belt, an Airport 2000 model AR/400SP. The operator reported that both the steering and the brakes became extremely stiff and unresponsive, making it impossible to avoid the collision despite the use of the handbrake.
Technical examinations revealed that the vehicle's battery was nearly depleted. While the battery indicator showed a healthy charge (two green lights) upon startup, this reading only reflected the voltage under no-load conditions. Once the operator engaged the drive motor, the sudden electrical load caused the voltage to drop significantly. This drop deprived the hydraulic pump of the power necessary to operate the power steering and power braking systems, rendering the vehicle's controls ineffective.
Findings
- The primary cause of the collision was the malfunction of the power braking and power steering systems on the baggage belt, resulting from a lack of sufficient battery power.
- The operator failed to detect the low battery state because the vehicle's battery status indicator provided an inaccurate reading under load.
- The battery voltage appeared sufficient at startup but dropped to a level incapable of supporting the hydraulic services once the vehicle was in motion.