What happened
On March 31, 2015, a Britten Norman BN-2B-26 operated by a German airline was preparing for departure from Wangerooge. After the pilot removed the rudder lock, the aircraft taxied approximately 1,000 meters southeast and then 950 meters east toward the start of runway 28. During the initial climb following takeoff, the pilot identified a malfunction in the rudder control. After requesting assistance from another aircraft in the vicinity, the pilot confirmed via visual inspection that the rudder remained immobile despite pedal input. The pilot subsequently performed a safe landing at Harle airport using asymmetric engine power to maintain control. There were no fatalities or injuries among the pilot and eight passengers, though the aircraft sustained light damage.
The investigation
The BFU investigation focused on the structural failure of the rudder control linkage. Examination of the aircraft revealed that the rudder control rod had torn away from the clevis attached to the rudder horn. Approximately two-thirds of the rod section was missing, and the remaining portion was bent backward. The investigation also noted damage to the three rudder hinge points. Metallurgical analysis conducted by the Institute for Joining and Welding Technology (ifs) determined that the failure was a ductile overload fracture. Microscopic examination showed evidence of shear failure, including slip bands and shear webs, with the final fracture occurring as a ductile overload. The material, an aluminum-copper alloy, showed no structural defects, though increased hardness was noted in the fracture area due to deformation hardening.
Findings
- The rudder control rod failed due to a ductile overload fracture.
- High wind loads, driven by a severe storm with strong, gusty winds, were transmitted to the control linkage during taxiing.
- Meteorological data confirmed that a storm system was present, with winds at nearby stations reaching up to 60 knots with gusts as high as 76 knots.
- While the pilot was highly experienced and the aircraft was properly maintained, the wind conditions were at the extreme edge of the aircraft's operational limits, and the maximum allowable taxiing wind speed was likely temporarily exceeded during the taxi phase.
Safety action
- The aircraft operator has since updated its operational procedures to reduce the maximum allowable wind speed for taxiing from 55 to 50 knots.
- The BFU issued a safety recommendation (03/2016) advising the manufacturer to more comprehensively evaluate potential wind loads on the vertical stabilizer resulting from specific taxiing wind directions and speeds to mitigate future risks.