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American Bonanza Society Control Cable Turnbuckle Recommendation Notice Number: NOTC8499
American Bonanza Society Control Cable Turnbuckle Recommendation
The American Bonanza Society (ABS) posted an article on January 30, 2019, that addressed some concerns over corrosion found on aileron and rudder cable turnbuckles hidden under the safety wire and one occurrence where the rudder cable turnbuckle failed. All of these occurrences happened where the turnbuckle is positioned beneath a heater duct or in the case of the rudder cable, the overheat inlet air duct.
After reviewing the original article, the FAASTeam feels it would be prudent to disseminate the information again to ensure all affected aircraft are inspected. Below are important excerpts from the ABS article.
The ABS is still in the beginning stages of gathering information. They cannot exclude any model of Bonanza, Baron, Debonair or Travel Air at this point. ABS will be making recommendations once they have a better handle on the data. For now, ABS recommends having a mechanic remove the safety wire and visually check the turnbuckles, and replace the turnbuckles if there is any sign of fatigue cracks or corrosion.
So far this issue has only been found in aileron cable turnbuckles in Bonanzas at the point the cable passes under the heater duct. The condensation from that duct may promote corrosion on the turnbuckles beneath the heater duct. If condensation is found in this manner, then this would confine this issue to Debonairs and Bonanzas, excluding Barons and Travel Airs. ABS might also suggest mitigations besides cable replacement to address the hazard. However, at least one of the five known cases involve a fatigue failure of the turnbuckle at mid-shaft with no evidence of corrosion. Around 1984, Beech began using a clip instead of a safety wire design. In the post 1984 airplanes, the turnbuckles are in the wheel wells, not in the fuselage under the heater duct. These can be visually inspected without removing clips.
In all cases of turnbuckles using the safety wire design, the safety wire completely obscured the failure under the safety wire wrap; the safety wire in each case was all that was holding the control cables together. Therefore, to inspect for this type of failure, the safety wire must be removed to facilitate the inspection of the turnbuckle.
Clip-style turnbuckles may not be immune to this issue and should be inspected the same way as those secured with safety wire. The difference is that the clip-style turnbuckles are much easier to see, and therefore easier to inspect. In later models (generally post-1984) the turnbuckles are clip-style and located in the wheel wells. Although these turnbuckles may dry much better than those inside the fuselage, they may be exposed to even more moisture in the wells and should be inspected as well.
If you have further questions, contact the American Bonanza Society at:
American Bonanza Society 3595 N. Webb Road Suite 200 Wichita, KS 67226