What happened
On August 11, 2015, a Boeing 747-8 arriving from Newark, USA, landed at Frankfurt/Main Airport on runway 25L at 07:19 local time. After exiting the runway via taxiway M21, the aircraft proceeded through a series of taxiways toward parking position C15.
During the taxi maneuver, the aircraft turned left from taxiway N onto the parking stand. At this time, a passenger bus was positioned near parking position V127, moving in a left curve to pick up passengers from a recently arrived flight at position V129. As the aircraft maneuvered, the bus entered the path of the engine exhaust. A second passenger bus was also stationary at position V12 and was struck by the first bus during the maneuver.
The force of the jet blast caused a window to shatter on the right side of the first bus, between the forward and middle doors, and deformed a rear engine cover. On the second bus, two windows on the rear left side were destroyed. Approximately 70 passengers were boarding the second bus at the time of the incident, and one person sustained minor facial lacerations.
The investigation
The BFU examined flight data recorder (FDR) information and airport records. The FDR indicated that approximately 11 minutes after landing, the aircraft's heading changed from 070° to 330° over a 35-second period. During this interval, the groundspeed fluctuated between 1 and 7 knots. Crucially, the FDR recorded an increase in engine power, with the N1 (fan speed) of engine #4 rising to 50%, while other engines remained at lower settings or were inactive.
The investigation also reviewed airport regulations and the airline's operating manual. Frankfurt Airport's traffic rules mandate a safety distance of 125 meters for vehicles behind aircraft with jet engines. Furthermore, the airline's manual specifies that breakaway power should be limited to 40% N1.
Findings
- The primary cause of the damage was the increased engine thrust applied to the number 4 engine during the turn.
- The passenger buses were positioned within the path of the jet blast.
- The aircraft's N1 speed on engine #4 reached 50%, exceeding the airline's recommended limit for breakaway power.