What happened
On 12 August 2000, a Cessna 172 RG, registered ZS-KSV, was conducting flight training in the D200 Training Area, north of Cape Town. The flight, operated by Cape Aero Club, involved a student pilot and an instructor practicing recovery from an incipient spin. During the maneuver, as the student pilot attempted to recover from a left-hand incipient spin by applying right-hand rudder, an audible snapping sound occurred. This was immediately followed by a total loss of rudder control. Despite the mechanical failure, the crew successfully recovered the aircraft from the spin and proceeded to perform a safe landing at Cape Town International Airport. There were no injuries and no fatalities resulting from the incident.
The investigation
Following the event, investigators examined the rudder pedal assembly of the aircraft. The inspection revealed that cracks had formed within the sheet metal structure of the rudder pedals. Furthermore, the investigation established that the torque tube bearings had reached a state of significant wear. This degradation likely permitted excessive movement between the two torque tubes, which in turn caused the torque tube gears to become misaligned. This misalignment led to the slackening of the rudder control cables.
Findings
- The primary cause of the loss of control was the misalignment of the torque tube gears.
- Worn torque tube bearings allowed for excessive movement within the control system.
- Structural cracks were present in the rudder pedal sheet metal.
- The aircraft, a 1981 model, had accumulated 5,858 total airframe hours.
- Current maintenance protocols do not mandate specific inspections of this particular system during Maintenance Program Intervals (MPIs).
Safety action
Given the prevalence of this specific aircraft type and age in flight training environments, it is recommended that airworthiness authorities notify aircraft owners and Approved Maintenance Organizations (AMOs) regarding these findings. This measure is intended to ensure that the potential for rudder control failure is addressed through more rigorous inspection standards.