Not only do you need a new magic box in the cockpit, but also the servo and communication systems that make the control surface respond to the command.
For years, simple autopilots like the Century IIB or III and the standard Piper system have been good enough for most light aircraft, but the development of the new integrated flight systems has meant that some of the older autopilots will no longer do the job as they are close to impossible to interface.
This is a major consideration in any avionics upgrade because you will not be able to get the full value from your shiny new glass cockpit without an integrated autopilot.
So before you settle on upgrading your panel, have your avionics expert check out your autopilot to see if it’s up to scratch.
Compatibility issues may be solved by selecting a flight deck with a built-in autopilot.
Even if you stay with the standard instruments, most modern autopilots can be slaved to an HSI, CDI, heading bug or even a GPS.
This takes the hard work out of long, droning straight-and-level legs, freeing up your hands and brain to do other things.
These are the traditional benefits of having ‘George’ fly the plane, but the value of an autopilot as a rescue instrument can’t be undervalued should you stray into IMC.
Autopilots don’t get the leans.
Your first decision will be whether you want a single-axis or twin-axis system.
Single-axis systems will hold either the pitch with elevator or the roll with aileron.
You will have to provide the input to the other yourself.
This is not a selection thing, the system will be designed to do only one and you won’t be able to change between modes.
A twin-axis will do both, enabling true ‘hands-off’ flight.
S-Tec
Now a part of the Cobham avionics conglomerate, S-Tec is the most prolific manufacturer of autopilot systems, having taken over the mantle from Century.
Some avionics installers now believe that an S-Tec system is the only real option for a GA aircraft.
Certainly their range is wide enough to cater for just about every need, and there are a lot of them appearing in upgraded panels.
Their range starts with the single-axis roll systems that fit into the standard 75mm instrument hole rather than add to your stack.
The S-Tec 20, 40 and 60-1 will follow a number of heading inputs, including the VOR, your own heading bug, LOC and GPS.
The 60-1 model also has course intercept capability and dual nav inputs.
The S-Tec 30 and 50 are twin-axis systems with altitude hold via pitch control.
Manual electric trim and GPSS roll steering are options for the low-end of the S-Tec range.
S-Tec’s star is the 55X.
This one is shaped to go in your avionics stack and is compatible with the large portion of flight directors, FMS and glass cockpit systems.
Its features cover just about everything you will need your autopilot to do.
Bendix King KFC 225
This is not the ordinary autopilot found in most GA planes.
It is a more sophisticated unit that borrows a lot from the flight directors found in regional and wide-body aircraft.
It is available in both two-and three-axis varieties, with the second including a yaw damper.
Being all-digital, it speaks languages common to many flight decks and therefore can be integrated without too much fuss.
As well as the ability to follow the heading bug or NAV, the 225 has control-wheel steering and GPS roll steering, which, when following a GPS plan, will anticipate turns earlier, making the angle of bank in the turn gentler.
It has some impressive safety features, such as an automatic disconnect if it senses excessive pitch, roll and acceleration.
Voice messages and alarms are used to warn the pilot if something out of the ordinary happens.
Quite a handy unit when you look at it closely.
Century Flight Systems
Many pilots would have had their first autopilot experience with the Century IIB or III system for GA aircraft.
Those marques are no longer available, and spares for them are becoming difficult to get, so if you are keen on this brand, it might be time to upgrade to one of their modern units.
The Century I is a basic single-axis autopilot that slots into the standard 75mm hole in the panel.
It is all-electric so vacuum failures will not affect it.
Turns of up to 200 deg per minute can be done by a pilot-controlled knob and VOR/LOC tracking is standard.
The Century I uses a tilted rate gyro to sense the rate of turn and the lighted turn indicator includes ball for slip/skid indications.
For something with a bit more, Century offer the 2000.
This is an upmarket unit that has a remote annunciator panel so the critical lights can be located in a more convenient place.
Standard functions include approach, NAV and heading holds and altitude hold and the system can be upgraded to include a flight director and yaw damper, effectively converting it into a three-axis unit.