Skip to main content

Control Cable Turnbuckles Update

ABS Full Member
Posts: 954

Posted 1/24/2019, reposted 1/30/2019:
Control Cable Update
ABS will be making recommendations once we have a better handle on the data. For now we suggest having your mechanic remove the safety wire and visually check the turnbuckles, with replacement if there is any sign of fatigue cracks or corrosion. The airplane rigging is not affected as long as the turnbuckle is not turned. Of course the turnbuckle must be re-safetied after inspection.

So far this issue has only been found in aileron cable turnbuckles in Bonanzas, at the point the cable passes under the heater duct. This leads to speculation—not confirmed at this point—that condensation from that duct may promote corrosion on the turnbuckles underneath. If this is indeed found to be a factor, this would confine this issue to Debonairs and Bonanzas, but exclude Barons and Travel Airs. It might also suggest mitigation’s besides cable replacement to address the hazard. However, at least one of the five known cases at this point involved a fatigue failure of the turnbuckle at mid-shaft with no evidence of corrosion.

We’re not yet certain precisely when the change occurred, but approximately 1984 Beech began using a clip instead of safety wire design. In these airplanes the turnbuckles are in the wheel wells, not in the fuselage under the heater duct. These can be visually inspected without removing clips.

We simply do not have enough data yet to make any specific recommendation other than visual inspection and replacement on condition if needed. In part this is because we are waiting for data from the NTSB that will only be forthcoming after the US Federal government shutdown. ABS will provide updates as we learn more.

Posted 1/30/2019 - 6 months ago
|

Replies

ABS Full Member
Posts: 954

What we know so far is that we have seen six cases of aileron cable turnbuckle failure and one of rudder turnbuckle failure. All seven occurred where the turnbuckle is positioned beneath a heater duct or, in the case of the rudder cable, the overheat inlet air duct. This leads our ABS Technical Advisors to believe the failures [b]MAY[/b] be related to condensation off those ducts--we don't know that yet for certain. That said, in one if the aileron cable turnbuckle failures there was no sign of corrosion. It simply broke apart in mid-shaft.

This is different from the Australian issues several years ago when the cables themselves failed. [b]Beechcraft Safety Communique 322 [/b](https://www.bonanza.org/globalassets/aircraft/safety-communiques/sc-322---flight-controls-cable-system-inspections.pdf) and the [b]ABS Flight Controls Inspection, Maintenance and Rigging Guide[/b] (https://www.bonanza.org/globalassets/migrated/pdf/flight-controls-flaps-and-trim-manual.pdf) address actions that should already be occurring during annual inspections to detect these sorts of failures.

In all cases with safety wires (post 1984 or so have clips instead) the safety wire completely obscured the failure; the safety wire in each case was all that was holding the control cables together. Hence to inspect for this failure mode the safety wire must first be removed, something rarely if ever done. As long as the turnbuckles are not turned it does not change the rigging to do this and then re-wire the turnbuckles. We're finding that many earlier airplanes already have replacement control cables with the clip-style connections. It may be that future replacement cables should be of this type to facilitate inspections for this issue.

Clip-style turnbuckles may not be immune to this issue and should be inspected the same 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, but there was apparently no single serial number cut-in break) the turnbuckles are clip-style and located in the wheel wells. These should be inspected too--they may be exposed to even more moisture in the wells, although they may also dry much better than those inside the fuselage also--and because they do not require removing the cabin interior and carry-through spar cover, they will be less time-consuming and costly to inspect.

We’re still in the beginning stages of gathering information. We cannot exclude any model of ABS-type airplane (Bonanza, Baron, Debonair or Travel Air) at this point. I’m trying to assemble a conference call of all ABS Technical Advisors for later this week, with the goal of providing a preliminary report and initial guidance for owners. I expect our preliminary recommendation will be essentially what I wrote above, with the important request that owners report their findings—good and bad—to me at asf@bonanza.org so we can better measure the true impact on the fleet one way or the other.

Posted 1/30/2019 - 6 months ago
|
Quote
ABS Full Member
Posts: 2

Hi Tom,

1980 V35B D-10309. Four turnbuckles in the wheel wells (2 in each). I cleaned them up, took pictures and sent them to my IA. He said they looked fine...no problems noted. They all had the clips.

Best,
Rich

Posted 3/31/2019 - 4 months ago
|
Quote

Control Cable Turnbuckles Update