Control Rigging: Critical, Yet Forgotten

Having the aircraft properly rigged per the maintenance manual can pay back big, and even avoid component failure and loss of control.

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Who has been working on this airplane? That was the question we would often ask in the shop when an airplane would come in for autopilot troubleshooting and we found control cable tensions so low you could strum a tune with them. Oftentimes it was to troubleshoot pitch and roll problems where the autopilot would deviate from the selected altitude or blow through the desired course. Then there were pilots who would complain the airplane wasn’t making book speeds, the controls weren’t as responsive as they once were, or the airplane wouldn’t fly straight and level. All are symptoms of rigging problems.

Owners give it little thought, and it’s a maintenance item that should be checked during annual inspection, but it often gets dropped. Moreover, when faced with the hefty shop labor to properly rig the airplane the way the manufacturer’s maintenance manual prescribes, many owners put it off. That’s a bad idea, especially when investing in a new autopilot. Read on for a lesson in control rigging 101. 

DIY Rigging Check

It’s easy to get complacent and not even recognize there’s a rigging problem. That is until you fly a similar model and notice how much tighter the controls feel, how it’s easier to keep in trim or how it flies just a touch faster than yours. Before taking it to the shop, do some checking yourself. Here’s a review.

As shops will attest, the specialized tools needed to precisely analyze and adjust the rigging are expensive, but aren’t needed for a general status check by non-mechanics. Look for some early clues by paying close attention to control surfaces, and how they feel when manipulating them: Is the trim tab bent? Do the controls feel stiff? Does the aircraft wander about the roll and pitch axes and is it a chore to accurately trim? It can be argued that observing an aircraft’s state of trim is subjective, but there is nothing at all arbitrary about diagnosing an out-of-rig airplane. 

For starters, bring the plane to a level area of the ramp where you can run the engine. Verify that the ground is level, then level the airplane laterally. You can do this using the leveling points specified in the airframe maintenance manual, although on many aircraft, you can simply put a bubble level across the pilot’s and copilot’s seat tracks. You could also let some air out of one main tire, provided the attitude isn’t such that you will have to make one tire flat to level the wings. Be sure the struts are equally level, and that one is not stuck extended or retracted. Don’t forget to compensate for the lack of weight in the pilot’s seat. Have someone of equal weight sit in for you.

With the airplane in perfect lateral level, adjust the turn coordinator so the inclinometer ball is perfectly centered. This could mean removing the false panel to access the instrument’s mounting screws, which are elongated to allow adjustment. Eliminate parallax (the apparent displacement of an object due to a change in the position of the observer) by adjusting the seat to the position you normally have it in flight—and your head in an equally normal position. When you are satisfied the instrument is perfectly level and the ball is centered from where you sit, retighten the mounting screws. If this is a steam gauge airplane, make a similar adjustment to the attitude indicator while it’s fully erect. You’re only concerned with lateral level here—the airplane may or may not be level with pitch at this point—so don’t be concerned with the horizon’s pitch display.

Next, make some checks outside the airplane. Get a straightedge of the appropriate length and check each cockpit-adjustable trim tab for fairness. The cockpit indicators may indicate neutral, but they may be lying. Get out and make sure they are actually in a neutral position, which is fair with the trailing edge of the control surface the tab is attached to. If there is disagreement between what the indicators show in the cockpit and the actual position of the tabs, make a note of it and mark the actual neutral position on the trim housing in the cockpit. 

From the outside of the airplane, make sure that the cowl flaps retract uniformly and completely. Also check for looseness. Note that some cowl flap systems are designed so that the flap trails slightly in flight. Read the manual.

Check the wing flaps and make sure they retract together and come up fairly even. Stand at one aileron-flap juncture and hold their trailing edges together. Does the outer trailing edge of that aileron line up with the trailing edge of the wingtip? If it does, is the control yoke or stick level? If you see the opposite aileron is level with the flap and wingtip, you may have picked up some valuable clues. A sagging aileron or flap may be the cause of tremendous trim drag. However, unless you have found something terribly awry, check your airframe manual before leaping to possibly erroneous conclusions. For most designs, though, the trailing edges of the flap, wingtip and aileron should fair together to form a straight line or smooth curve.

Flying It

Don’t ignore a stiff or binding pitch trim. The command wheel should be smooth and the trim action should be linear.

Set aside some time where you can fly the airplane to focus fully on the rigging. Pick a calm day (turbulence will make this more difficult) where you can fly VFR without interruption. If possible, ask a mechanic to come along. Fill the fuel tanks and empty the baggage compartments. Use caution, as some aircraft are out of their balance envelope in this configuration, so you might have to compensate. Remember that you are looking to achieve lateral balance in the air. If you nearly always have passengers, then you will want to proceed to check your rigging based on a balanced lateral load (which means taking an equally weighted passenger along). If you fly solo most times, check the rigging based on the unbalanced load of your butt in the left seat. 

Once airborne, accelerate to the normal cruising speed in level flight. Feel free to use the elevator trim, but leave the rudder or aileron trim tabs neutral. Come off the rudder pedals and roll the wings level using aileron (providing a wing was low) referencing the attitude instrument. With the heavy wing leveled and the skid ball centered (without your input), note the rudder trim indicator’s position and mark the exact position. Masking tape works. Note whether the heavy wing is still heavy. Chances are it’s not, or at least not as bad as it was. If it still takes some aileron input to hold one wing up, adjust the aileron trim to compensate.

Note the aileron trim indicator’s setting the same way you did for the rudder trim. On a side note, if your instructor never clued you in, this is really the correct way to trim an aircraft for level flight. Some refer to it as the tail-first method. Trim the elevator to hold proper pitch, then the rudder to get the ball centered and finally the ailerons to get the wings level. This is easier in aircraft with cockpit-adjustable trim tabs or no movable tabs. If the tabs are put into a neutral position and you still find that constant control pressure is required to keep the ball centered and the wings level, the airplane’s rigging demands more scrutiny. Its inability to fly straight and level without having one or more trim tabs deflected means it is losing airspeed to trim drag.

Shopping Tips: Hit The Logs

If you’re shopping for a used aircraft, the attention paid to the aircraft’s rigging will speak volumes for how it was maintained, overall. Start with the logbooks and look for the magic words that indicate it’s been rigged—especially if the airplane has been painted.

You should see something along the lines of: “Control surface rigging checked and found to be in conformity with manufacturer’s specifications.” We’ll bet that you come up empty for the majority of aircraft you research.

The teardown during paint projects could lead to control rigging – and balance – issues. It’s a good time to perform a rigging job and of course, weigh the aircraft when the paint work is finished.

If the aircraft has been painted, you might see wording from the paint shop that a control surface has been balanced, but this doesn’t mean all surfaces were rigged. 

In some instances, an airplane may have been improperly rigged right out of the factory. If it’s never been checked, it’s still improperly rigged. An especially hard landing can cause a change in the rigging. In these situations, external damage (perhaps wrinkled skin) should be visible, but is often missed. It’s possible the damage may be more than cosmetic. Even if it was repaired, it may not be ready for flight.

One case of unrelated maintenance and rigging problems that comes to mind involved a Piper Saratoga. During the course of the repair, the nosegear and engine mount were removed for repairs. New nosegear bushings and straightening/rewelding of the engine mount was accomplished. Reassembled and with the nosewheel centered, it was obvious the rudder was slightly cocked to one side. The new repairs had corrected a past asymmetry problem, which now showed up as the cocked rudder.

Previous damage showed up during a shop inspection of a high-powered twin. It was noticed that the left aileron ground-adjustable trim tab was intentionally bent to nearly maximum deflection, and an extra ground-adjustable trim tab had been installed on the right aileron (it, too, had been bent to nearly maximum deflection). The cockpit-adjustable rudder tab had been adjusted quite far off to one side. Closer examination of the airframe revealed an extra stall strip fitted to the right wingtip.

The wing was bent—apparently in an exceptionally hard landing years before. Attempting to compensate for the asymmetric airframe, mechanics, through the years, had bent the aileron tabs to their maximums. No doubt this airframe wasn’t making full speed and its new owner was blindsided with major repairs. In our estimation, a deeper prepurchase evaluation might have helped.

Who’s Gonna Do It?

Done right, properly rigging a complex twin or single could mean sizable teardown and as much as two days of shop time, especially if aging components need replacement. That’s often the case as airframes age and the multitude of small parts in the control system wear out.

If you’re committing to a new autopilot installation, we strongly suggest picking a shop that has experience rigging the controls. We recently heard a nightmare story of a complex twin that had a new Garmin autopilot installed, but the installing shop didn’t have the capability to rig the cables per the aircraft’s maintenance manual. When the owner retrieved the aircraft, he was disappointed to find the old autopilot performed better than the new digital one. He ended up bringing it to a shop that specializes in the type. That added time and more expense for a task that should have been done before installing the autopilot. 

Last, control rigging  (or lack of it) can pose a safety of flight issue. We remember a taildragger that ended up in the weeds in a stiff crosswind because the rudder cables had so much slop the pilot couldn’t obtain full deflection when he needed it the most. A $1000 rigging job could have ultimately prevented a $10,000 repair.


This article originally appeared in the February 2021 issue of Aviation Consumer magazine.

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Larry Anglisano is a regular AVweb contributor and the Editor in Chief of sister publication Aviation Consumer magazine. He's an active land, sea and glider pilot, and has over 30 years experience as an avionics tech.

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9 COMMENTS

  1. I am an A&P who admittedly always has something to learn, but I had a hard time following some of this.
    “As shops will attest, the specialized tools needed to precisely analyze and adjust the rigging are expensive, ”
    I’m probably missing the obvious, but I’m trying to think of anything special for the rigging for light singles or even twins off the top of my head – you’d need a digital protractor which you can pick up for around $20. You’d need a cable tensiometer which is not cheap but one most people use is under $200 new. I can find one on the used market for half that and it’s easy to calibrate with a weight, or make the one in the Kit Planes article which is actually nicer than what is in my toolbox.
    Most planes have some sort of jig that sits on the tail upper airfoil to form a flat surface to set the protractor on to get the required measurement in the TCDS. There’s a template for that in the MM and it takes an hour or two to make one from scrap lumber but I don’t know anyone who ever actually paid for the Cessna or Piper, etc. part for the jig.
    I don’t interpret 14 CFR 43 Appendix A for a living, but this seems to be instructions for non-mechanics to adjust instruments required for airworthiness. Not sure if that is a legit preventative maintenance task authorized in Part 43 for owner pilots to perform. You do you.

    Not to sound flippant but the way to check your plane’s control surfaces is per the MM to the deflection numbers in the TCDS. I know this article ends with “read the manual” but that’s actually the opener, not the closer. Some of these other instructions seem to be possible red herrings. From my admittedly incomplete experience, there are very few of these 50+ yr old planes that haven’t slightly deformed by a couple of mm from thousands of TO/L cycles, assuming they were ever built or rigged true. Not sure if you’re going to necessarily see wrinkled skin etc., you might think there was one big event but it just seems like these poor mules have hauled a lot on their backs for so long and are a little bent no matter what, even if they never had a major hard landing event.

    For advice, I would avoid buying from anyone who’s always braggin on their $400 annuals. If I sign your annual, I complied with Appdx. D Pt 43 (c)(5) and (j), meaning I inspected all systems, including the control system, per MM’s procedures. In an annual, that goes without saying and I don’t itemize every system the MM details a required check of, so I’d only log any control surface rigging adjustments. But be sure I followed the MM and I ran a cloth over every inch of 7×19, ensured each pully moved freely, fairleads are all good, check tension and deflection numbers per spec.
    Sadly many mechanics are under the impression that they can attest to current airworthiness of your plane by simply ticking off the 30 or so literal items in Appendix D to Part 43. If that’s you’re idea of an annual inspection, rigging might be the least of your problems

  2. I agree with you Carl, as a shop owner we see the gambit of problems with aircraft. We regularly check and adjust cable tensions. Had a Cherokee six in a while back where all the cable turn barrels were at max adjustment and the cables were less that 8lbs. We ended up replacing all the flight control cables.

    The $400 annuals are alive and well being done by mechanics with no insurance and certainly no current and up to date tech manual subscription.

    • I was thinking the very same thing! The phrase “tensions so low you could strum a tune with them” just does not sound logical. I think maybe there is a typo and the author meant to say “tensions so low you could NOT strum a tune with them” or maybe “tensions so high you COULD strum a tune with them”.

  3. Thanx for your lengthy but thoughtful comment, Carl R. As an A&P and former A&P Instructor, I agree with and support your position. I do not blame anyone for trying to save money, but basic instincts should sound an alarm when a person who earns his living performing inspections and repairs offers a ridiculous price for an annual inspection or time-consuming repair. I may not agree with Larry A. on every point, but I give him credit for opening this issue for us with his article.

    Now for a new twist: EAB’s. Experimental Amateur Built airplanes are a blessing for pilots when it comes to saving money. Since EAB owners are “exempt” from Part 43, there is no annual, but a “Conformity” Inspection instead. OK, none of this is news, but where does an A&P performing a Conformity Inspection go to reference the correct rigging numbers on an airplane whose builder (FAA calls this person: “Manufacturer” on the Airworthiness Certificate) passed on years ago?

    • The A&P or non builder owner can check for the data in the builder’s/manufacturer’s log, check with a kit manufacturer, a type club, or a set of plans, or the owner of another one, or another A&P or repairman who maintains one like it, or someone who has built one, or someone who is building one. Many possibilities. I probably missed some. The EAB industry is mature now with good support.

  4. For EAB it is a Condition inspection, not a Conformity inspection. The term comes from the definition of airworthy, which in a nutshell is conformity and condition. An EAB does not have a type design (TCDS, etc.) so there is no conformity or approved data to reference for the annual/Condition inspection. That is why it is called a Condition inspection, the signing mechanic or repairman can only attest that the aircraft is in a “condition safe for flight”. This also means an EAB can never be called airworthy, it can’t be by definition. FYI I currently own two EABs.

    Most EAB aircraft have drawings or other data for the flight control rigging and travels. If you don’t have any hard data it would be difficult to do the rigging.

    As an A&P, IA and maintenance instructor I also find some of the suggestions in this article to be beyond the legal abilities of the owner/operator.