The FAA’s FAASTeam published a safety notification this week echoing concerns outlined by the American Bonanza Society in January. The intention was to ensure all Bonanza owners were aware of the potential problem.
In short, ABS reported that control cables were failing at the swaged ends where they meet with adjusting turnbuckles. These turnbuckles can be secured either by clips or with safety wire that’s wrapped around the shank of the swaged cable end. It’s the latter configuration proving to be an issue.
The ABS says it is “aware of six recent cases of failure of the swaged end of flight control cables at the turn buckles in Beech piston airplanes. Four were in aileron control cables, one in an elevator control cable and one in a rudder control cable. Two of these cases are currently under investigation by the U.S. National Transportation Safety Board. Failure of a control cable connection at the turn buckle will result in loss of use of the associated control surface(s) and probable loss of control of the aircraft in flight. NOTE: This condition is not related to the control cable failures that were subject of an Australian (CASA) Airworthiness Directive in 2012.”
Some of these broken swaged ends were found in cables exposed to the elements but some were hidden in overhead panels. According to the ABS report, “Safety wire prevents visual inspection of the affected areas. Further, the safety wire itself tends to trap moisture and debris from the lower fuselage, potentially accelerating corrosion in the aileron turn barrels. Safety wire must be REMOVED in order to inspect the swaged ends for the type of damage we have seen. In two cases the swaged ends of the cable had failed between the safety wire hold and threaded end completely and the safety wire was all that was holding it together. Later airplanes have turn barrels held by clips that make visual inspection easier, and some pre-1970 airplane cables may have been replaced with the clip style turn barrels. The aileron cable turn buckles are located in the wheel wells post 1977 with this type of cable, which may be exposed to moisture but tend to dry from air flow in flight.”
The ABS is urging owners to check these areas within the next 20 hours and is requesting that the FAA add a specific callout to inspect under safety wire to the existing Special Airworthiness Information Bulletin CE-12-18 having to do with control-system inspections in Bonanzas.