What happened
On June 2, 2015, at the EPLL airport, a Boeing 737-800 was undergoing standard pre-departure procedures. Following the completion of a walkaround inspection by a ground handler, the aircraft's engines were started in sequence, beginning with engine number 2 followed by engine number 1. Once the nose gear steering bypass pin was removed and the signal was relayed to the flight crew, the crew confirmed stable engine parameters and signaled that they were ready to proceed.
The crew requested to terminate intercom communications and were awaiting a specific visual signal from the left side of the aircraft to begin taxiing. However, after the intercom plug was disconnected, the ground handler encountered difficulty closing the protective socket cover due to a jammed latch. The ground handler requested assistance from the ground controller to resolve the mechanical issue. During this process, both the ground handler and the controller moved out of the flight crew's line of sight.
As the ground personnel began to move away from the aircraft after resolving the latch issue, the Boeing 737-800 initiated taxiing without having received the pre-established visual clearance. Because the aircraft was moving at a low speed, the ground personnel were able to move to a safe distance before any collision occurred.
The investigation
The PKBWL investigation focused on the sequence of communications between the flight crew and the ground personnel. The investigation established that the ground handler and the ground controller were temporarily obscured from the crew's view while attempting to fix the intercom socket cover. The investigation also confirmed that the established protocol for visual signaling was not followed by the flight crew before the commencement of movement.