What happened
On the night of 11 November 2017, a Boeing 747-400 ERF, registration TC-ACR, was preparing for a scheduled cargo flight from Maastricht Aachen Airport to Jeddah. During the take-off roll on Runway 21, the aircraft was accelerating through approximately 30 knots when the number four engine suddenly experienced a power loss.
The resulting asymmetric thrust caused the aircraft to yaw sharply to the right. The flight crew attempted to maintain the centerline using nose wheel steering, differential braking, and left rudder, but the deviation could not be corrected. The aircraft subsequently exited the runway and entered the soft ground on the right side of the airfield. The incident resulted in substantial damage to the aircraft, though there were no injuries to the crew.
The investigation
The Dutch Safety Board examined the mechanical state of the engines and the crew' and cockpit environment. Investigators analyzed the flight data recorder and cockpit voice recorder to reconstruct the sequence of events. The investigation included a borescope inspection of the engine components and laboratory testing of various engine parts, including the high-pressure compressor (HPC) blades, fan blades, and fuel pump.
Engine examinations revealed that while some components, such as certain HPC blades, showed evidence of wear and fatigue from previous flight cycles, these were not the primary cause of the sudden stall. However, the investigation did find that the fuel gear pump showed cavitation damage and signs of having been run without fuel, leading to its disposal. Additionally, some temperature sensors failed visual inspections due to corrosion.
Findings
The primary cause of the runway excursion was the pilot's inability to maintain directional control due to prolonged asymmetric thrust following the loss of power in engine #4 at a low airspeed. The loss of thrust was triggered by a compressor stall.
Several contributing factors were identified:
- The crew did not immediately retard the thrust levers to idle, which is the necessary action to arrest deviation when the rudder is not yet effective. It took approximately eight seconds for the levers to be moved to idle.
- The 'startle effect' likely prevented the crew from following standard rejected take-off (RTO) procedures immediately following the loud bang and engine failure.
- The use of active noise-cancelling headsets by the captain may have hindered the immediate perception of the engine failure.
- The crew felt time pressure to depart due to impending airport night-flight restrictions.