What happened
On 24 February 2024, during a training flight at Blackbus and Blackbushe Airport, Surrey, a Cessna 152, registration G-BSZW, experienced a sudden loss of right rudder control. During takeoff, the instructor noticed the student pilot appeared to lack sufficient rudder control and prompted a right rudder input. Despite the student's efforts, the aircraft failed to respond to right rudder commands, though full left rudder authority remained functional.
The instructor took control of the aircraft and, after confirming the lack of response to right rudder inputs, levelled the aircraft at circuit height. The instructor briefed the student on the situation, and the remainder of the flight proceeded without further incident, with the aircraft landing safely. There were no fatalities and no injuries to the crew or passenger.
The investigation
Following the incident, investigators examined the rudder assembly and discovered that the right rudder cable had detached from the rudder bellcrank. The examination of the bellcrank revealed that the component had fractured across its full width at the attachment point, with the tip of the bellcrank having separated during flight.
Physical evidence showed that the inboard edge of the bellcrank had been rubbing against the aircraft's fuselage rub-plate. This contact had caused significant mechanical wear, stripping the paint and exposing bare metal. Furthermore, the investigation found that the bolt stack used to attach the cable clevis did not match the manufacturer's specifications; it included an incorrect top-hat style bush and an additional washer, suggesting the attachment hole had been previously oversized.
Findings
- The primary cause of the failure was stress corrosion cracking (SCC).
- The cracking originated on the inboard edge of the bellcrank where mechanical wear from fouling against the fuselage had removed the protective paint and exposed the metal to corrosive elements.
- This wear reduced the effective cross-section of the bellcrank, increasing the stress on the remaining material.
- The investigation could not determine the exact cause of the bellcrank fouling against the fuselage, though possibilities included misalignment or incorrect rudder stop settings.
- The aircraft had not been subjected to the manufacturer's supplemental inspection (27-20-02), which calls for inspections every 100 hours or annually, meaning the developing crack went undetected.