Cessna Navomatic 400

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USAF-LT-G

Pre-takeoff checklist
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Jan 30, 2017
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USAF-LT-G
I'm considering a purchase of an aircraft that has a Cessna Navomatic 400 A/P, with a KCS-55A HSI, Garmin 530W, and GTX-320 (ADS-B out) though i know this component probably doesn't really matter in this context.

I've heard from others that the 400A and B A/P is a fine auto-pilot, but I don't believe this is a 400A or 400B. I think it's just a straight up 400. It looks exactly like this, except the "HEADING" wheel is removed (I believe because of the HSI Capture):

734722225114032RoaC.JPG


From what I know, it tracks and does HDG just fine, I assume from somehow coupling with the HSI. But it's been said that the altitude capture doesn't work properly. It functions, but the hold is sketchy. I don't really know much about this A/P and having a hard time finding any useful information on it. So I have some questions:

1) Can this be repaired? If so... where?
2) Is it worth getting repaired?
2) With the other equipment installed, assuming the A/P was working properly, can it fly say an LPV down to minimums? Or are we talking a stepped down approach only?

I don't really know much about it, so I appreciate the insight from those "in the know" :)
 
Anyone have any opinion or experience as to the capabilities of the 400 with modern equipment and coupling?
 
The picture you posted is a straight Cessna Navomatic 400 Autopilot. It used an attitude gyro for lateral and pitch sensing and a directional gyro for heading deviation sensing. A pressure sensing device maintains selected altitude. It was designed to allow climbs/descents or altitude hold; the owners manual does not indicate that it will capture any altitude. It was also designed to track a VOR Omni bearing with up to a 10 degree crab angle. Beyond that correction, the manual directs the use of the heading knob in 5 degree increments to reduce stand-off. The system was also designed to be used to follow magnetic headings selected by using the heading control knob. Mine worked just fine until removed for a panel upgrade. I’ve no idea if it can be adapted to use a gps input instead of the DG, though I suspect it cannot use digital inputs of any kind, whether lateral or vertical.
 
One of the cool features of the Cessna 300/400 series is that the select use of the heading mode or turn/wings level mode directs the AP from either the DG (vacuum) or TC (electric). This means you still have some level of functionality if you have a vacuum failure (you still have a wing-leveler/turn rate-based AP) or electric failure.
 
I had a 400A that worked well for the first few months I owned the plane. It turned into a roller coaster. It had all been pulled and sent to Autopilots Central about a year prior. Instead of sinking money in a 40 year old computer I bit the bullet and upgraded to the STEC 3100. Night and day in terms of performance and safety enhancements. Whatever you decide, if a fully functioning autopilot is important to you, I’d have 20-35K set aside for that depending on the specific plane and modern approved options. Good luck with your plane shopping!
 
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