What happened
On 14 September 2002, a Boeing 747-300, registration TF-ATH, was undergoing pushback at Madrid-Barajas Airport, prepared for a flight to Mexico D.F. The aircraft had already experienced significant delays due to maintenance issues and a fuel leak observed during refueling. During the pushback process, the flight crew followed a sequence to start engines 1, 2, 3, and 4.
As the crew was starting engine 3, a communication misunderstanding occurred between the flight crew and a ground technician. The crew misinterpreted the technician's instruction regarding engine 3 rotation as a request to apply the parking brake. This resulted in an abrupt braking action, causing the tow bar to strike the nose gear leg. Following the incident, the crew requested clearance to taxi back to the terminal finger.
The investigation
The CIAIAC investigation examined the hydraulic and brake systems of the aircraft, the engine starting sequence, and the cockpit environment. The investigation noted that the cockpit was crowded, containing the pilot in command, co-pilot, flight engineer, a relief co-pilot, and a passenger. The investigation also reviewed the ground technician's statements and the sequence of engine starts.
Findings
- The primary cause of the incident was that the electrically driven hydraulic pump (ACP) was not manually reconnected after it automatically released during the initiation of the engine 4 starting process, which was ultimately discontinued.
- The crew was distracted by several contributing factors, including the behavior of passengers who were refusing to fly and standing in the cabin, which required the chief cabin attendant to enter the cockpit multiple times.
- The crew failed to complete the "after start" checklist as detailed in the operator's manual.
- The crew failed to connect the alternative or emergency hydraulic systems once the loss of brake pressure was identified.
- A communication error occurred when the crew misunderstood the ground technician's verbal instructions during the engine start sequence.