What happened
On October 22, 2014, a Boeing 747-422 operated by a US-based airline landed on runway 25L at Frankfurt/Main Airport. The flight had departed from Chicago, USA, the previous evening, carrying 291 passengers and 16 crew members.
The aircraft was performing an ILS approach with a target speed of 157 knots. During the flare maneuver, the aircraft encountered a gust. The pilot flying responded by using aileron to correct the aircraft's attitude. While the flight data recorder (FDR) showed the airspeed remained within the required stabilized approach parameters, it also recorded a right bank of 5.5° approximately two seconds after the aircraft'le weight transitioned to the ground.
Upon reaching the parking position, the crew discovered damage to the underside of the number four engine (the outermost right engine) nacelle. There were no injuries to the passengers or crew, though the aircraft sustained light damage.
The investigation
The BFU investigation relied on statements from the pilot in command and an analysis of the flight data recorder (FDR). The FDR and cockpit voice recorder (CVR) were both recovered and found to be fully functional and readable.
Investigators examined the physical damage to the engine, which included abrasions on the engine inlet ring, the lower engine nacelle, and the reverser components, as well as cracks and broken pieces on the reverser lower fairing. The investigation also reviewed the airline's flight manual and operational procedures regarding stabilized approaches and aircraft bank angles.
Findings
The investigation established that the contact between the engine and the runway was caused by a right bank of 5.5° occurring during the landing roll. The airline's flight manual specifically warns that with the main landing gear compressed, the outboard engine pod can contact the ground at a bank angle of approximately 6°.