History of the Flight
On 14 August 2013, at 23:20 local time, a Boeing B737-800 (registration G-GDFJ) operated by Jet2.com as a commercial air transport flight under IFR from Dalaman, Turkey to Budapest, Hungary, experienced a technical issue during the climb after takeoff. When the flap control lever was moved to the retract position, the flap actuators in each wing shifted to different extents, resulting in a slight aerodynamic asymmetry. The system monitoring flap movement detected the asymmetry and stopped further retraction.
Analysis
The investigation, conducted by the Transportation Safety Bureau of Hungary, evaluated flight data recorder information and procedural documents, including the captain's event report. The defective equipment—a gearbox in the flap operating mechanism on the right-hand side—was impounded and sent to the manufacturer for detailed testing. The test report documented signs of wear and cracks at several points of the internally toothed fitting sleeve (for receiving a spline shaft) located at the end-of-wing side of one of the transmission shafts adjacent to the drive box. The seal ring responsible for supporting the fitting sleeve and insulating the drive box was absent. This absence allowed the force transfer connection point to shift slightly, leading to heavy wear and damage over time.
The IC determined that the fault was caused by the missing supporting and insulating ring. No records of the ring's absence were found in the gearbox history provided by the operating company, so the manner and date of its disappearance could not be determined.
Findings
The cause of the incident was the absence of the seal ring at the wing-end side output of the drive box, which is responsible for supporting the fitting seal and preventing long-term wear due to loose fitting of the force transfer point.
Safety Recommendations
No safety recommendations were issued, as the IC did not find circumstances warranting them.
Personal Injuries
No personal injuries occurred during the occurrence.