What happened
On 8 April 2003, a Boeing 737-73V, registration G-EZJR, was performing a scheduled passenger flight from Luton Airport to Belfast Aldergrove. During the takeoff roll on Runway 08, the aircraft experienced a sudden and significant lateral jolt at the moment the nosewheel was lifted from the ground. While the aircraft's handling returned to normal once airborne, the crew noted the severity of the movement. The Senior Cabin Crew Member reported that the disturbance was so intense that it appeared the aircraft might veer off the runway.
Following the incident, the flight crew consulted company checklists, but no specific procedures existed for such an event as the aircraft was functioning normally. After communicating with company operations and engineering, the decision was made to return to Luton for a technical inspection. The crew increased their approach speed by 10 knots as a precaution against further uncommanded inputs. The aircraft landed safely at Luton with no injuries to the 5 crew members or 119 passengers, and no damage to the airframe.
The investigation
Investigators analyzed flight data to determine if a mechanical failure or pilot input had caused the deviation. The data confirmed that the rudder control and yaw damper systems were fully operational and responding correctly to inputs during both taxi and takeoff. Analysis showed that while there were minor heading deviations during the initial ground roll, the sudden lateral acceleration of 0.21 g occurred specifically at approximately 128 kt, just before rotation. This acceleration happened without any input from the pilots or the flight control systems.
Engine parameters were checked and found to be delivering symmetric thrust, and brake pressure was found to be normal. The investigation also ruled out jet blast from other aircraft, as no other planes were using the nearby runup bay at the time. While the preceding aircraft was of a similar weight and had departed only three minutes prior, the investigation noted that any wake turbulence encountered would likely not have caused such significant control issues according to standard separation guidelines.
Findings
- The aircraft's mechanical systems, including the rudder, yaw damper, and engines, were functioning correctly.
- There was no evidence of pilot error or uncommanded control surface movement initiating the lateral force.
- An unspecified atmospheric disturbance acting on the aircraft at the point of rotation was the identified cause of the sudden yaw and lateral acceleration.