Century III Autopilots

[AggieMike88]

A few of the aircraft types that I'm browsing on the interwebz have the Century III Autopilot.

I have no experience with this system. Can I get some information about the system from the standpoint of utility, easy of use, added value to purchase/selling, and anything else you want to add.

 

[Clark1961]

Century has most of the docs on their website for their products. Be careful about models because the III may not be the same as the IIIc.

If you're looking at a IIIc I can fill in some details. If you're looking at a III, I believe Ted's Aztruck has one. They are different critters...

Correction: I have a Century III coupled which Piper called the Altimatic IIIc. The Century III manual with appropriate options describes my system which was installed under field approval based on an STC for the Arrow.

 

[poadeleted20]

It's a pretty fundamental 2-axis autopilot. In roll you get basic stabilization, roll command, heading bug track, and needle-based nav tracking including BC mode but not much for interception. In pitch you get basic stabilization, pitch command, and altitude hold -- and don't engage altitude hold with more than about 200 fpm climb or descent rate unless you want a roller coaster ride. I believe there is a GPSS roll steering module available as an add-on. Works off the attitude and heading indicators, so a vacuum failure kills it unless you spend a pile of money to go all-electric.

 

[Ted]

I've flown many variants of the Century III. The 310 has a straight up Century III, the Aztruck has an Altimatic IIIB (Century IIIB), and the Navajos I flew had the IIIC in it.

They're all basic 2-axis autopilots, and they all work similarly well (which is not very). The IIIB and IIIC will intercept and track a glide slope if working properly, and will also adjust your electric trim. The 310 doesn't have electric trim, so I don't know if the straight III will do electric trim if so equipped. However, this does make it annoying to do any pitch functions besides altitude hold with the autopilot (and even then you have to make sure it's trimmed out prior to engaging) since otherwise the AP is fighting the trim.

The Aztruck's pitch functions never worked properly entirely. It would hold an attitude fine (for a while) but the altitude chamber never worked, so it wouldn't hold altitude. The IIIB is supposed to allow altitude preselect. The IIIC in both Navajos I've flown has a tendency to have a significant trim runaway. One Navajo would run down, the other one would run up.

Assuming the computers in them are working properly, all of them will track a heading, nav (VOR/GPS) or a localizer just fine. If you upgrade to an Aspen, without a special converter box (which is expensive) the nav/LOC functions need input from the heading bug, so on the 310 I have to set the heading bug as well as the course needle (well, the course needle sets itself automatically) to make the autopilot work properly with it.

They all work fairly similarly, which is simple operation. You have switches that turn on the roll, heading, pitch, and altitude hold functions. For heading you select which source you want it from. One of the options is "LOC BC", meaning back course Localizer. When I got the Aztec, I liked this feature since it would fly back course localizers for me. After 1000 hours with that plane, not only have I never used that feature, I've come to realize I probably never will. Not only are there few BC LOCs out there, I'd end up hand flying one myself if I came upon one.

The autopilots require the attitude indicator for feed, which means if the connector on the back comes off or the AI is going bad, they don't work great. Had both those problems.

Century IIIs are great for teaching you to be inherent distrustful of autopilots. While I think this has its training uses, it really isn't helpful in an autopilot that you're trying to use for something like, say, flying the airplane. Griffin Avionics at Hyannis, MA did all the work on the Aztec's IIIB, and they did a great job for a reasonable price. Unfortunately, you can only put so much lipstick on a pig.

In buying an airplane, I would say a Century III is better than nothing. Dr. Bruce has managed to keep his working fine for a long time, so has Lance (gismo), and if I put a new AI in the 310 (the current one that drives the AP is old and not doing so great) then it would probably do well. But overall, I'm of the mindset that I would rather wait until the Century III craps out entirely, and save up the money for an STec of some form that will work better with the Aspen and be more reliable. Hmm. Now that makes me wonder, would the AI from the Aztec work in the 310? Anyone know enough about the IIIs and IIIBs to know if that would be the same? Bruce, Lance? The Aztec's AI works great.

 

[Ted]

Also, I don't mean to imply that the IIIs are junk. But, they are 40+ year old autopilots, and many of them probably aren't working at 100% after years of neglect and ownership by people who don't understand them. By many, I mean probably all of them that don't belong to Lance or Bruce. I include myself in that.

 

[Clark1961]

There are some subtle differences between the III and the IIIc with autotrim. The III senses tension in the elevator wires (I believe) and the IIIc senses voltage to the elevator servo. The principle difference is that the III can be a handful when the autopilot goes offline when flying an approach while the IIIc is fairly benign.

None of the III series are being made and the OEMs for some of the parts are no longer producing those parts (servo motors in particular).

They can be made to work well either by Autopilots Central in Tulsa or Century in Mineral Wells. It will be $$$$$$$$ at either site. Before the Aspen install, the IIIc on the 'kota would fly a very fine coupled ILS. I'm still getting used to it with the Aspen and may have a few bugs to work out (this is mostly because I don't fly much IFR).

There are other autopilots that are much better in terms of advertised capability. The Century products can be made to work but it will generally take a lot of time and money and parts can be hard to find.

 

[Ted]

There are other autopilots that are much better in terms of advertised capability. The Century products can be made to work but it will generally take a lot of time and money and parts can be hard to find.

That's probably the best summary. The only better you can do on advertised capability is altitude preselect. But the various KFC units and M4s are way, way better in execution.

 

[gismo]

Century has most of the docs on their website for their products. Be careful about models because the III may not be the same as the IIIc.

If you're looking at a IIIc I can fill in some details. If you're looking at a III, I believe Ted's Aztruck has one. They are different critters...

AFaIK Ted's autopilot was a Piper Autocontrol IIIb which is quite a bit different than a Century III although I do believe it was made by Edo-Aire which became Century at some point.

Despite it's age, the Century III is a fairly capable unit. Fully optioned with a HSI, a radio coupler, and a glideslope coupler it can track a VOR or GPS course, hold a heading, intercept a course (from a fixed 45° angle), hold pitch, hold altitude, and capture/follow a glideslope (ILS or LPV). The roll control functions (heading, tracking, etc) can be activated without the pitch axis, something that many newer autopilots don't allow. It does lack several features found in more modern units such as altitude pre-select, constant vertical speed climbs and descents, all angle intercept, CWS, go-around, and there's no flight director option. There is no microprocessor, built in self test or fancy annunciator panel either.

If you add GPSS driven by some WAAS GPS navigators you gain the ability for hands off autopilot flown course changes (bends), DME arcs, procedure turns, and holds. That combination can track an entire approach complete with the missed portion terminated in a hold with almost no input from the pilot other than power and configuration changes (you do have to manage the pitch axis on the miss).

If the electronics are healthy and the servos are in decent shape (they typically need their motors cleaned up every 1000 hours of operation).

It relies on pitch and roll feedback from an air powered attitude indicator so if you lose vacuum you lose the autopilot as well. Almost all Century IIIs were installed with manual/auto electric trim


There are some potential maintenance issues: The Century III is a very old design and the earliest versions were plagued with problems due to a circuit board fabrication method that used "griplets" instead of plated thru-holes for connections. If your autopilot has any of those, you can pretty much guarantee you will need to replace them. Fortunately used circuit boards with a better design can usually be found at a reasonable price.

Century also used a connector style in their wiring harness which tends to develop poor connections over time. There is a newer version of the same connector which can be used for replacement but it would be a fair amount of effort to replace every one. I have successfully resolved a few connector problems by "tweaking" the female socket pins with a dental pick and so far haven't had to replace more than one connector.

 

[gismo]

There are some subtle differences between the III and the IIIc with autotrim. The III senses tension in the elevator wires (I believe) and the IIIc senses voltage to the elevator servo. The principle difference is that the III can be a handful when the autopilot goes offline when flying an approach while the IIIc is fairly benign.

The Century III autotrim comes in two flavors. Some use mechanical switch contacts that activate based on elevator cable tension and there are two or three versions of the sensing mechanism, all of which can be problematic. A plus on these is the ability to bring the aircraft roughly into a trimmed condition while hand flying (press the rocker trim switch down without moving it forward or backward) and since the sensor is between the servo and the elevator, pilot input with the pitch axis engage will NOT cause the trim to move. The later version uses an electronic sensor which moves the trim based on the average voltage applied to the pitch servo instead of the mechanical one.

FWIW, I've spent about $3000 maintaining my Century III over about 16 years of ownership and 3000 flight hours. Two thirds of that were for two overhauls of the pitch servo (the first one wasn't done properly) and the rest went to a circuit board replacement and to tracing an intermittent problem in the main amp (aka computer).

 

[AggieMike88]

Is there a simple upgrade path from the Century III's to the Stec's?

Is it as simple as items on/behind the panel or does the entire system and servo's need to be changed?

The info provided is helping with the learning curve, especially when evaluating a purchase that has the Century.

 

[SCCutler]

Is there a simple upgrade path from the Century III's to the Stec's?

Is it as simple as items on/behind the panel or does the entire system and servo's need to be changed?

The info provided is helping with the learning curve, especially when evaluating a purchase that has the Century.

It would be a completely new install. Figure 13 to 20 grand, depending on which S-Tec...

 

[AggieMike88]

Speaking of evaluating a purchase, if I was test flying an aircraft equipped with any autopilot, what is a decent routine to ensure the functions are working as advertised? How to find that an original function isn't functioning?

 

[AggieMike88]

It would be a completely new install. Figure 13 to 20 grand, depending on which S-Tec...

Whoa... I figured it would be steep, but not quite that steep.

I might be re-evaluating some of the aircraft I've tagged into a spreadsheet...

 

[SCCutler]

If I found a good plane with a C-III, if all the parts 'n' pieces were there, I'd budget for an Autopilots Central overhaul (couple grand).

 

[AggieMike88]

If I found a good plane with a C-III, if all the parts 'n' pieces were there, I'd budget for an Autopilots Central overhaul (couple grand).

Good to know.

 

[gismo]

It would be a completely new install. Figure 13 to 20 grand, depending on which S-Tec...

Avidyne is in the process of certifying their DFC90 autopilot (a very capable very modern microprocessor controlled system) on several aircraft with the ability to interface with existing Century III servos (and some others). I think they're talking about $12-15k installed.

 

[SCCutler]

Avidyne is in the process of certifying their DFC90 autopilot (a very capable very modern microprocessor controlled system) on several aircraft with the ability to interface with existing Century III servos (and some others). I think they're talking about $12-15k installed.

...well...

...that, plus the Aspen they require to give attitude reference, right?

 

[gismo]

Speaking of evaluating a purchase, if I was test flying an aircraft equipped with any autopilot, what is a decent routine to ensure the functions are working as advertised? How to find that an original function isn't functioning?

Get the POH supplement and check it for an extensive pre-flight check. Beyond that your best bet is to find someone familiar with the autopilot and connected systems and have them accompany you on a test flight.

Basics to cover:

Roll Axis:
Bank angle command, heading hold, heading change (move the bug 90° left and right), VOR/GPS intercept and tracking.

Pitch axis:
Pitch hold and altitude hold without porpoising, vertical speed, altitude pre-select, GS intercept and tracking to 200 AGL, go-around mode, and transition from climb/descent to altitude hold without offset (ends up staying at the altitude you were at when altitude hold was engaged instead of climbing or descending 50 feet or more).

Pitch trim:
Manual trim works in both directions, auto trim responds to power changes and pitch or VS commands.

 

[wabower]

Bob Ferguson at APC can fix more AP problems over the phone than most shops can fix with a shop-full of techs.

If I found a good plane with a C-III, if all the parts 'n' pieces were there, I'd budget for an Autopilots Central overhaul (couple grand).

 

[NineThreeKilo]

.... added value to purchase/selling, and anything else you want to add.

Well it's better then a loran, I guess :wink2:

Yesterdecades autopilot, if its not something like a stec or comparable I just view it as unreliable -> not a selling point worth anything.

I've played with enough of those old autopilots to not bother using them, older altimeters, DG, compass etc. are ok, but when you get into tech things like GPS, autopilots and that sort, the value dropoff with age is STEEP.

 

[Clark1961]

Speaking of evaluating a purchase, if I was test flying an aircraft equipped with any autopilot, what is a decent routine to ensure the functions are working as advertised? How to find that an original function isn't functioning?

Get to about 5,000 agl and turn the darn thing on. Be prepared to disengage immediately...

When I bought the 'kota the previous owner told me the wing leveler function worked but the altitude hold didn't. He was optimistic to say the least. Had to rebuild the computer, the trim amp, the trim servo, and replace the altitude chamber before it would work. Of course once it worked it was just fine. The trim amp turned out to have a cold solder joint after the rebuild but I didn't figure it out until the warranty expired sou I got to pay for repair of that one. It has been flawless ever since.

 

[Ted]

As expected, Lance knows more about my own autopilot than I do.

Lance, do you have any thoughts if the AI gyro from the Aztec's Altimatic IIIB would interface with the 310's Century III? That would probably fix some of my annoyances with it.

 

[Ted]

Mike, I wouldn't necessarily say not to buy a plane with a C-III. I have over 1000 hours with them, probably closer to 1500. But if you want a rock solid autopilot, you would be better off finding an STec or a King KFC unit installed. In all fairness, I do think most of the Century issues stem from people not knowing how to maintain them. I've seen Autopilots Central charge thousands of dollars, I'm sure fix some problems, and then the AP still doesn't work. So while they are very good, some units are just that bad.

You may also want to consider cost of an STec in purchase price of a plane. If you see a plane that is in excellent condition other than a non-working C-III and the price reflects that, you could install the one you want.

 

[AggieMike88]

You may also want to consider cost of an STec in purchase price of a plane. If you see a plane that is in excellent condition other than a non-working C-III and the price reflects that, you could install the one you want.

That's one of the things I'm taking away from the thread. If there is documented evidence of recent repair and that's proven in flight, then I might add some dollars to my valuation. If not, then adjust my valuation as appropriate.

 

[Ted]

Out of curiosity, what sort of aircraft are you looking at?

 

[TMetzinger]

Get the POH supplement and check it for an extensive pre-flight check. Beyond that your best bet is to find someone familiar with the autopilot and connected systems and have them accompany you on a test flight.

Basics to cover:

Roll Axis:
Bank angle command, heading hold, heading change (move the bug 90° left and right), VOR/GPS intercept and tracking.

Pitch axis:
Pitch hold and altitude hold without porpoising, vertical speed, altitude pre-select, GS intercept and tracking to 200 AGL, go-around mode, and transition from climb/descent to altitude hold without offset (ends up staying at the altitude you were at when altitude hold was engaged instead of climbing or descending 50 feet or more).

Pitch trim:
Manual trim works in both directions, auto trim responds to power changes and pitch or VS commands.

This is a good list. Be sure and check all your nav sources if the autopilot has switching to couple to them, i.e. NAV1/NAV2/GPS/GPSS.

 

[wabower]

Only those on Dave Ramsey's approved list. But so far he's avoided buying any of them, which puts him pretty high on the smarter-than-the-average-bear roster.

Out of curiosity, what sort of aircraft are you looking at?

 

[AggieMike88]

Out of curiosity, what sort of aircraft are you looking at?

Ones with wings, engine, semi-comfy seat, and can afford to purchase and operate


Currently the primary targets include mid- to later C177's, Cherokee 180D's, Archer's, Cheetah's and Tigers.

But I'm also keeping track of a few C182's and Mooney 201's

Mission profile is 1-2 person 150nm local fun flying, once to twice a month 3 person with bags weekend trips to Katy, TX. Twice maybe thrice a year longer trips such as to Denver. And a good IFR platform

Many aircraft I spot have the STEC's in them. I've had a few rides in aircraft equipped with them and the pilots have good things to say. But to date, I haven't spoken directly to pilots who have the C-III or been in an aircraft with one.

 

[AggieMike88]

Only those on Dave Ramsey's approved list. But so far he's avoided buying any of them, which puts him pretty high on the smarter-than-the-average-bear roster.

Thank you Ranger Smith! I'll save a pic-a-nic basket just for you!

 

[Ted]

I'd give a hard look at Mooneys. There are some good deals out there on M20Fs. Comanche 250s represent a good deal, too. I like flying both very much.

 

[Sac Arrow]

All of the Arrows I've flown had III's. No pitch control or trim functions. Crude but a whole lot better than nothing at all.

One weakness that seems to be inherent with the Century III planes I've flown is that they don't track a heading bug well, they tend to rock the wings. They track a nav signal better.

 

[SCCutler]

I'd give a hard look at Mooneys. There are some good deals out there on M20Fs. Comanche 250s represent a good deal, too. I like flying both very much.

...or go right to where you really want to be, and get a Bonanza.

 

[gismo]

As expected, Lance knows more about my own autopilot than I do.

Lance, do you have any thoughts if the AI gyro from the Aztec's Altimatic IIIB would interface with the 310's Century III? That would probably fix some of my annoyances with it.

AFaIK they both can use a 52D67 or 52D167 horizon gyro.

 

[AggieMike88]

...or go right to where you really want to be, and get a Bonanza.

So, when are you going to tempt me to the dark side???? Now that you got your Bo put back together and all....

 

[Ted]

AFaIK they both can use a 52D67 or 52D167 horizon gyro.

Excellent. Then I think I'll swap the units between the Aztec and the 310. Maybe that'll make my Century III work better!

So, when are you going to tempt me to the dark side???? Now that you got your Bo put back together and all....

Bonanzas have very smooth controls. Beechcraft in general - I just can't figure out how they make it so that even a 40+ year old version feels brand new. Meanwhile the 310's yoke does show some play in the controls.

For me, the visibility out of a Bo isn't my cup of tea. There's just something about them that makes them not appeal to me in the same way as a Mooney or a Comanche.

But, as we know, what I like is usually what others don't.

 

[Sam D]

A bit of necropost here...but here's the situation:

'76 Lance with Century III autopilot. It's currently experiencing pitch issues. That is, when altitude hold or pitch is engaged, the plane immediately pitches up. I believe these units have some type of altimeter built in and there is likely a problem with it.

Here's my question: we have an Aspen installed. The Aspen EA100 was recently approved for the Century III to provide pitch and roll info. Could the installation of this potentially fix the problem? Or does it just replace another part of the AP system (i.e. the gyro)?

 

[Thomas Fankhauser]

I have a CIII in my 67 Bonanza that was installed as original equipment. It is working fine except for slight a slight porpus at altitude hold engagement. Just found after reading this thread and talking to Matt Greer at Century that I have auto trim. Unfortunately the auto trim is not functioning. It is engaging and trim wheel is firm but it is not trimming. I have the original servos that only autopilot central used to repair.
Question: has anyone had Autopilot Central work on any parts of their CIII in the last year or so?
Matt will be working on this autopilot and sending components to them for repairs when necessary. I’m just soliciting some recent feedback.

 

[Heftiger]

I had a problem with altitude hold in my CIII. It turned out that the vibration isolators on the altitude canister had completely collapsed. To test the theory I stuck some foam under it to help with vibration. Solved the issue.

 

[Heftiger]

I have a CIII in my 67 Bonanza that was installed as original equipment. It is working fine except for slight a slight porpus at altitude hold engagement. Just found after reading this thread and talking to Matt Greer at Century that I have auto trim. Unfortunately the auto trim is not functioning. It is engaging and trim wheel is firm but it is not trimming. I have the original servos that only autopilot central used to repair.
Question: has anyone had Autopilot Central work on any parts of their CIII in the last year or so?
Matt will be working on this autopilot and sending components to them for repairs when necessary. I’m just soliciting some recent feedback.

The auto trim is an option. A nice one to have, but should work without. When you turn off the trim, does the altitude hold work?

 

[Thomas Fankhauser]

The auto trim is an option. A nice one to have, but should work without. When you turn off the trim, does the altitude hold work?

Yes it does and never knew i had it. Sometimes I have to help the trim. Meaning the trim will be 1-2 dig up but maintaining level flight but off 50’ from where I set the Altitude. If I “help” the trim by putting it in the correct for that attitude / speed it holds the originally set altitude. This is especially the case when I have tips full and close if not at gross.
I thought maybe the auto trim being in repair will hel this along with the porposing it does at gross weight.??