Autopilot repair facility

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    Hello fellow members. I fly a 310P out of Lawrenceville Ga. (LZU) near Atlanta and am experiencing problems with my Navomatic 400A autopilot. Does anyone know of or heard of a good Navomatic autopilot shop located in the south East.

    Thanks, David


    We had work done at Carpenter Avionics in Smyrna, TN on our 800B. They might be able to help you. The cost to keep the AP running may astound you. I would recommend an evaluation by a shop and then a worst case scenario repair estimate. Probably the best shop in the country is Autopilots Central in Oklahoma. I know it is a bit far, but they know the Cessna AP better than anyone else and it may actually save you money to take the airplane to them. At some point you may need to decide if it is worth fixing or more cost effective to replace.

    quote DLYNN:

    Hello fellow members. I fly a 310P out of Lawrenceville Ga. (LZU) near Atlanta and am experiencing problems with my Navomatic 400A autopilot. Does anyone know of or heard of a good Navomatic autopilot shop located in the south East.

    Thanks, David

    What’s it doing?


    There are two shops that are highly recognized experts on older Cessna/ARC equipment, particularly the autopilots:

    Executive Autopilots in Sacramento, California (KSAC)

    Autopilots Central, Tulsa OK (KTUL)

    I’m sure there are others, but these are widely known as “the experts.”

    Finally, I’d add that the 400A may not be worth too much in repairs. The 400B and 800s were pretty good units, but the 400A enjoys a reputation as, well, cargo. I’d probably at least have a conversation with one of the experts to get their take.


    You can easily spend enough money fixing it to install a new style Auto Pilot. Once you start down the path you are committing to fix it and a some point you almost reach a point of no return where you have spent so much money you have to fix it.


    I would highly recommend Mayday Avionics in Grand Rapids
    Altho’ I have not actually used them since I was able to sort out my problems myself with Bob Webers advice, I was impressed with his understanding and ability to communicate a solution. That is after presenting my control problem to several other shops. Subsequently I have come up with a test sequence to prove operation and also a section that I use every pre-flight. Here it is for any of you who would like a bit more insight into how it should function. This of course is not a full description only to clear up ‘my’ hazy understanidng.

    AutoPilot and KLN-90B GPS CHECKOUT


    1. OBS Mode should track HSI OBS selector when looking at MODE 2 or NAV 3 page. Select either page and turn the OBS to see bearing reading change.
    a. Refer to Operating Manual (or page 5-35) and Install Manual

    2. Check altitude Alert Audio. Refer to Operating Manual 3.15. reset to 300’ for WARN Altitude. If no WARN Altitude adjustment is enabled and no Alert Audio is heard then pin 38 of the GPS is grounded. Note that the Alert should sound when within 300’ of Airport Elevation provided the Altitude Baro setting is correct.

    3. Check Message and Waypoint Alerting Lamp with Lamp test on the MD-41 Switch Unit. Refer to Operating Manual 3.8.6 and 3.17.

    a. Message lamp should flash whenever GPS sends a message.
    b. Waypoint Lamp should flash whenever GPS signals Turn Anticipation and Waypoint alerting is in the GPS as seen by a Flashing Arrow preceding the waypoint identifier on the Waypoint page.

    4. Check that the ILS Disconnect operates to disable the GPS whenever an ILS frequency is selected on the #1 Nav Receiver, but GPS is selectable and works when any other frequency is selected.

    5. If AP fails to hold course and does not follow or seem to turn ‘right’ from either the ‘Bug’ or the OBS selector, – try using the AP ‘Pull and Turn’ knob to turn the aircraft. This will prove the aileron actuator is ok or not (located in R Wing).

    6. TESTING AP action during Pre-flight.

    a. Set bug to exact ‘000’ on HSI
    b. Pull AP Control Head ‘Turn’ knob out
    c. Switch AP ‘On’ while holding Aircraft Control Wheel firmly. It may pull left or right vigorously but this is not abnormal, and only means the Heading Bug is not on Zero or the Trim Control is not balanced out
    d. Turn ‘Turn knob’ to balance out Control Wheel
    e. Push Knob ‘In’
    f. Turn Bug to balance out Control Wheel, note if on ‘000’ or not
    g. Set Bug to exact ‘000’ again
    h. Adjust AP Control Head ‘Trim’ control to balance out Control Wheel
    i. Now Aircraft will fly the heading Bug correctly

    Any comments appreciated


    I’d put in a strong vote for Autopilots Central in Tulsa, OK. Talk to Bob Ferguson. They still have 400A parts available and they can keep your unit running. They’ll give you an honest assessment of your unit, and the costs to fix your unit vs. replacing it. They are great people, and I would recommend them without reservation.

    Bob Joyce
    Omaha, NE
    CE-414A, CE-310J


    Hands down, the best shop I have ever been to in trying to get an old autopilot fixed was El Paso Avionics/Aviation. A couple of years ago, after a decade of messing around with other shops all over the country, the unit failed (again) as I happened to be passing through ELP. The FBO sent me over to El Paso’s shop, and they had it fixed within 24 hours…and apologized for taking that long.

    Turns out the problem was an intermittent short in one of the circuit boards that had probably been there since it left the factory in 1979. El Paso took the entire autotpilot apart, right down to the circuit boards, and figured out that was where the problem was. There being no ready replacement available, they sprayed the board repeatedly with a freezing agent until they were able to locate and fix the tiny short. It remains fixed today.

    As I recall, the bill for all this was on the order of $1500, which given my earlier expenditures seemed to be a bargain.

    Kevin E. Ware, ATP


    I recently had my autopilot 400b removed and sent to Autopilots Central in Tulsa for inspection and repairs. I was having trouble with intermittent failures of altitude hold and nav tracking. They went through the computer and replaced many parts. The bill was about $2000. Since then it has worked perfectly. I paid my local avionics tech about $200 to remove and reinstall the autopilot computer. The expense of autopilot test equipment and insurance makes local repairs impractical for many avionics shops. I don`t have any experience with the 400 A unit but would be inclined to follow the advice of Autopilots Central on this issue. Some times a flight to an autopilot facility and multiple test flights will be needed to resolve this type of problem. Good luck, Glenn Carwell C 340

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