What happened
At 2146 Eastern standard time, a Lufthansa German Airlines Boeing 747-430 was undergoing de-icing procedures at the central de-icing facility at Toronto / Lester B. Pearson International Airport. While the aircraft was being serviced, the operator of de-icing vehicle 13 noticed that the wing root remained contaminated. The driver attempted to contact the zone de-icing controller via UHF radio to request permission to reposition the vehicle to apply a second coat of fluid, but the transmission was lost in heavy radio congestion.
Believing the de-icing process was complete and the area was clear, the controller known as Iceman updated the signal board to "Exit Now" and authorized the aircraft to taxi. As the Boeing 747-430 began to move forward, the vehicle operator attempted to move the truck out of the aircraft's path. However, the right leading edge of the aircraft's wing struck the vehicle's boom, causing the truck to tip onto its right side. The operator of vehicle 13 sustained non-life-threatening injuries to the head, face, and leg, while the aircraft sustained damage to its wing skin.
The investigation
The investigation examined the communication protocols and staffing levels at the de-icing facility. It was established that on the night of the accident, only one zone de-icing controller was on duty, managing four de-icing pads instead of the usual three. This increased workload led to significant task saturation. Furthermore, the investigation found that the UHF radio frequency was heavily congested due to a lack of radio discipline among various staff members, many of whom did not hold formal radio telephone licenses.
Investigators also looked into the signaling process. The controller relied on a manual "de-icing strip" to confirm that all vehicles had returned to safe zones. Because the controller could not identify the specific request from vehicle 13 amidst the radio noise, the strip was passed to Iceman, signaling that the area was clear when it was not.
Findings
- The zone de-icing controller issued taxi instructions while de-icing vehicle 13 was still positioned in front of the aircraft's wing.
- Radio congestion and task saturation prevented the vehicle operator from successfully communicating the need to re-apply fluid.
- There were no standard operating procedures limiting the number of pads a single controller could manage or the number of users on the UHF frequency.
- The facility lacked a formal procedure for vehicles to return to an aircraft for fluid re-application.
- The controller relied on memory and a manual strip system that did not specifically track which teams were still active.