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Anti-Servo Tab Linkage

The Anti-Servo Tab (AKA ‘Trim Tab’) is connected to the (very strong) actuator cartridge by a rather slim control rod/control link. On the earliest models this rod is straight. On later models, it has a slight bend on the forward end. THIS LINK AND ITS HARDWARE IS A FLIGHT-CRITICAL PART!!!!I am in the midst of an exchange with a member who will remain anonymous. He ordered a hardware kit, and wished to return it, because ‘the bolts are much too small’. I have pasted in (below) my response to him. I would never have thought that anyone would have done what it initially sounds like has been done in this case. I cannot say with certainty, as I have not yet seen photos. But in light of the importance of this part, I advise every member (unless you have been KLUX’ed) to check this linkage for the proper size bolt (3/16″ diameter). There is also a proper type of bolt and nut, but that’s another story. The key aspect here is to make certain someone has not made the hole oversize for a quarter-inch bolt.


Whoa. Something is seriously wrong. The bolts I sent are the correct 10-32 (-3 size) special magnafluxed bolts. If they are much too small (reported as about 1/2 the size of the hole), something is very badly wrong, and it could prove deadly to you. The ends of that rod are VERY highly stressed for their size; that’s one of the reasons it uses special magnafluxed bolts and nuts, and special end bushings. There is supposed to be a hardened stainless-steel bushing in each end of the rod, which is roll-peined in place. It is not made to be readily removable. It sounds like someone may have knocked out the 3/16″ ID by 1/4″ OD bushings, and installed 4-28 (size -4) bolts, which are .250″ rather than .187″ in diameter. If so, the rod ends have been severely weakened, far beyond any reasonable limit. They do not have the hardened bushings which serve to spread out the load, while reducing the rate of wear in the much softer aluminum of the control rod. Beech does not allow any modifications to that rod. That rod, and those two bolts, are ‘Jesus parts’. If either end comes loose, you will die. If an aileron rod or rudder cable breaks, the plane remains controllable. But it is impossible to control the Stabilator if the Anti-Servo tab function is lost. It is not just a trim tab, as can be seen by its size and direction of movement. Its primary function is to increase travel resistance as the Stabilator moves out of trail. Without the tab, the Stabilator will slam fully against the up or down stop on its own, due to wind loads, and you cannot prevent it.

You are certainly welcome to return the kit; that’s no big deal at all. But please, DO NOT FLY THE PLANE until you can send me some photos of both ends of the control rod, so we can figure out what is going on here. An A&P-IA who is unfamiliar with the model probably would not detect this during Annual Inspections. It would have been done either by some prior owner trying to save a dollar, or some prior A&P who should have known better. They discovered play in the bolt-bushing interface, and their solution was to punch out the bushing and use a bigger bolt. Very bad news, if that is what we find. One accidental VNE event during a maneuver, or a limit load application during turbulence, could break an end of the rod. You must not take this lightly; please let me help you follow up on it.

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