Incident Overview
On September 30, 2005, a Boeing 737-300 operating a flight from Turin to Frankfurt/Main encountered a severe disturbance during its approach to Runway 25L. The aircraft was carrying five crew members and 90 passengers. At the time of the incident, the plane was flying at an altitude of 2,700 feet, approximately 9.8 nautical miles from the runway threshold.
Flight Dynamics and Response
The aircraft initially rolled 23 degrees to the right, a movement controlled by the autopilot. This was followed by a more severe roll of 62 degrees to the left. The crew disengaged the autopilot during this second phase and manually restored the aircraft to normal flight attitude. The landing flaps were set to position 1, and the airspeed was between 200 and 210 knots. The pilot continued the approach slightly above the glideslope until a safe landing was achieved.
Investigation Findings
The German Federal Aviation Office (BFU) investigated the event with support from the German Aerospace Center (DLR). Analysis of radar data, flight data recorder information, and meteorological conditions indicated that the Boeing 737-300 likely encountered the wake turbulence of a preceding Boeing 747-400. The 747 was approaching the parallel Runway 25R.
Simulations suggested that wind conditions caused the wake vortices to drift toward the path of the following aircraft. At the moment the autopilot was disengaged, the estimated distance between the two aircraft was 4.6 nautical miles. The analysis concluded that the Boeing 737-300 came into very close proximity with or directly struck a strong wake vortex generated by the heavier aircraft ahead.
Outcome
There were no injuries to passengers or crew, and no damage was reported to the aircraft or third parties. The incident was classified as a severe disturbance.