Unusual directional changes during takeoff roll of a Boeing 757-300 in Antalya

Event overview and flight development On 16 June 2000, a Boeing 757-300 passenger aircraft carrying 249 people was on a charter flight to Cologne. During the takeoff roll, shortly before liftoff, the aircraft made unintended directional changes with uncomfortable lateral accelerations and deviated several meters from the runway centerline. The pilot flying felt kicks in the rudder pedals while correcting. After liftoff, the aircraft and its systems behaved normally. Because a possible effect on controllability during landing was feared, the crew prepared passengers for an abnormal landing and declared an emergency to air traffic control on approach to the destination airport. Landing and taxiing to the parking position were uneventful. ## Investigation and findings The German Federal Aviation Accident Investigation Office (BFU) was informed of the emergency by an official at Cologne Airport. In coordination with the operator, the flight data recorder (FDR) was secured for analysis. The operator’s technical service inspected the rudder, wheels and brakes, and engines on site, but the cause was not resolved. The aircraft was transferred to the operator’s technical base in Frankfurt, where the entire rudder system was tested according to manufacturer instructions. Both yaw damper / stabilizer trim control units were sent to the manufacturer and found to be functioning normally. During inspection of the nose-wheel steering, it was found that the cable pre-tension was only 45 lbs instead of the 62 lbs required by Boeing, and that the neutral position of the hydraulic actuation was at 2° rather than within the specified 1.5°. Boeing informed the operator that B757-300 aircraft built between 15 November 1998 and 20 June 2000 had been fitted with control cables in the flight controls, brakes, and landing-gear actuation that had not been pre-stretched before installation. The affected aircraft was produced in 1999. The operator issued an engineering order to check and adjust cable tensions at every second A-check on its B757-300 fleet until no further changes were found. ## Flight data recorder analysis FDR data showed a sequence of directional changes during the takeoff roll, with time zero defined as nose-wheel liftoff. Starting about 23 seconds before liftoff, the aircraft’s heading shifted right at about 85 knots ground speed, corrected by the pilot with up to 25% rudder pedal input. Further shifts occurred at about 110, 130, 140, 150, and 155 knots, with pedal inputs up to 40% and a maximum heading deviation of 3°. At liftoff, the heading stabilized and the pedals and rudder returned to neutral. At speeds above 100 knots, the directional changes caused deviations from the runway centerline of up to 6 m and lateral accelerations from -0.2g to +0.15g. Pedals and rudder moved synchronously. Earlier flights also showed unstable directional behavior during takeoff rolls, but the incident exceeded the limits accepted by the pilot. ## Assessment and conclusions The investigation concluded that the aircraft had been fitted with control cables that had not been pre-stretched before installation. Over time, the nose-gear steering cable tension reduced enough to cause lag in nose-wheel deflection. When the rudder pedals were moved, the rudder responded immediately while the nose wheels lagged, adding their effect later and making the directional control sluggish. The pilot flying continually overcontrolled the aircraft as speed increased, producing growing deviations from the takeoff direction. It could not be determined whether the partly unstable rolling behavior was solely due to the manufacturing error or typical for the Boeing 757-300. Boeing issued a service letter on 31 October 2000 to operators of B737, B747, and B757 aircraft built between 15 November 1998 and 20 June 2000 about the manufacturing error, so the BBU did not issue a safety recommendation.