What happened
On 28 January 2019, at Singapore Changi Airport, a catering truck was performing routine food cart replenishment on an Airbus A350-900, registration 9V-SMS. During the process of unloading used carts and loading new ones, the truck's cabin platform began to drift downward on its own.
To correct the height, the truck operator attempted to use the front control panel but found it unresponsive, prompting him to use the rear control panel. Because the operator could not see the platform from the rear position, he relied on a colleague to monitor the height. As the platform was raised toward the aircraft, a safety shoe—intended to prevent door contact—was compressed between the platform and the aircraft door. Despite the operator attempting to stop the ascent, the platform continued to rise, eventually striking the aft-most right-side door (Door 4R). The impact forced the door upward, resulting in a twisted door hinge and damage to the adjacent door frame.
The investigation
Investigators examined the truck's mechanical functions and the effectiveness of the safety shoe system. While the control panels themselves were found to be functioning correctly, CCTV footage confirmed that the platform was lowering without any manual command.
Testing revealed that the truck's engine was running at an abnormally high idle speed of 1,200 RPM, compared to the manufacturer's recommended 900 RPM. This excessive speed generated enough hydraulic pressure to cause the scissor lift to drift downward under load. Furthermore, investigators discovered a critical design flaw: any manual command from the truck's control panels would override the safety shoe's automatic lowering mechanism, rendering the safety feature useless during manual height adjustments.
Findings
- The primary cause of the platform's uncommanded descent was an excessive engine idle speed of 1,200 RPM, which created unintended hydraulic pressure.
- The manufacturer's recommended 900 RPM setting was not clearly communicated to the operator or included in the maintenance manual.
- The safety shoe's automatic protection mechanism was bypassed because the truck's manual control inputs took precedence over the safety sensor's command.
- The use of the rear control panel prevented the operator from having a direct line of sight to the aircraft door during the adjustment.