Waypoints

From the smallest tube-and-fabric knockabout to the biggest business jet, general aviation is a highly diverse and often high-profile industry — but it is also a small industry. Everyone knows everyone else, and it seems as if every person you meet has worked for every other person. The histories of companies are as intertwined as the characters on the steamiest soap opera.

The size of the industry creates a folksiness that is by degrees charming and frustrating. It's charming that you can call up your airframe manufacturer and request some widget for your 1957 airplane; it's frustrating that it will take them three months to make it for you.

Still, I find remarkable the level of service that GA manufacturers are able to provide. Whether you have a problem with your airframe, engine, or avionics, chances are you can taxi up to the factory and get someone to take a look. Try showing up at the Chevy factory to get your Impala serviced and see what sort of welcome you get. Hello, Security?

I pondered all of this after having my autopilot tweaked a bit at the S-Tec Corporation factory in Mineral Wells, Texas. Climbing away from the factory, I flipped on the autopilot and watched it easily track the southwest bearing to Kerrville, Texas, home of Mooney Aircraft and my next stop. I had stopped at S-Tec because it was only a few miles out of the way and because I had never visited the little town just west of Dallas that has proclaimed itself the autopilot capital of the world. It's a big assertion for a little town of about 15,000. But, at least at the lighter end of GA, it's true. S-Tec and Century Flight Systems, both located on the airport at Mineral Wells, claim nearly 90 percent of the piston market.

As is often the case when you have more than one company making similar products in the same area, the two started as one. Don Mitchell began building flight control systems and radios in Mineral Wells more than 50 years ago. Eventually, the company, along with several other small aviation outfits, was purchased by Edo-Aire. And, as often happens when a company buys up a lot of smaller operations, it eventually began spinning the companies off again. It was at about this time that five employees at the autopilot division of Edo left the company and moved across the field to start their own operation. This new entity, called S-Tec Corporation, came into being in 1978 and shortly thereafter began shipping autopilots specifically designed for the retrofit market. Meanwhile, in 1983, Edo sold its autopilot division to an entrepreneur named Bill Eubanks. That entity was dubbed Century Flight Systems, adopting the name of its venerable and well-established product line.

S-Tec's plan to offer retrofit autopilots in the late 1970s could either be called brilliant marketing or plain lucky timing, because it was then that GA production reached its climax. Beginning in 1980, the number of new aircraft deliveries plummeted, devastating avionics manufacturers and everyone else associated with the industry. As a start-up, S-Tec had no place to go except up, and, by 1982, it had already established itself as a maker of quality and innovative products for a suddenly aging GA fleet. With a dwindling number of new aircraft available, owners began looking at ways to upgrade their existing rides, and S-Tec had a simple, upgradable flight control system ready to go. You could buy a wing leveler and easily upgrade later to a two-axis system without replacing any servos. If you needed a three-axis auto-pilot, S-Tec offered a yaw damper to round out your system.

The same basic systems are still offered today, although the line has grown dramatically to more than 60 flight-control products approved for more than 450 models of aircraft. Recent innovations include the System Twenty and System Thirty, two autopilots that take little or no additional panel space, except for the usual turn coordinator. Earlier this year, S-Tec introduced GPSS — GPS Steering (see " Pilot Products," September Pilot). When connected to a GPS that outputs roll steering data, an S-Tec autopilot with GPSS will fly an entire route with no input from the pilot. The pilot needs only to manage the vertical portion of the flights — climbs and descents.

S-Tec currently has more than 1,600 supplemental type certificates (STCs) to install its systems in various aircraft and is adding more at the rate of about five a month. When I was there, technicians were completing a system on an Aero-star 601P. Once approved for the 601P, STCs for other models of Aerostars will follow quickly.

You might ask why a company would need 1,600 STCs when there aren't nearly that many models of aircraft flying. In fact, virtually every permutation of every model needs its own STC. Ken Paul, S-Tec's director of marketing, points out that even certain airframe mods can invalidate an STC. More than one owner has been surprised to learn that his autopilot installation is no longer approved after adding an airframe or engine mod that affects the flight characteristics of the airplane. Airframe mods that affect only takeoff and landing characteristics — such as a STOL kit — typically do not affect an autopilot STC because the autopilot should be turned off during those phases of flight. However, if the mod affects the flight characteristics of the aircraft during cruise, for example, then the STC may be rendered ineffective. Regardless, S-Tec can often dip into its vast library of STCs to get a customer flying again quickly. Chances are that someone else with an S-Tec autopilot and the same model of aircraft has had the same mods installed.

All of the S-Tec autopilots are rate-based, meaning that they derive their position information from the gyro in the turn coordinator. Actually, they use the gyro to measure the rate of position change over time. Autopilots from other manufacturers often use position from the attitude indicator (called position- or attitude-based autopilots) or a combination of position and rate to keep the aircraft pointed in the correct direction. As you might expect, there are advantages and disadvantages to each.

Rate-based autopilots tend to be very reliable because the slower-turning, electrically driven gyros in turn coordinators fail less often than do the vacuum-driven gyros in attitude indicators. In addition, even with a vacuum pump failure, a pilot can still use a rate-based autopilot, so partial-panel flight can be less of a challenge.

Across the field at Century Flight Systems, the company will tell you that its current generation of products generally uses a combination of position and rate information to fly the airplane. The result is a more complex installation, but one that for the most part flies the airplane more crisply than a purely rate-based system, especially in turbulence and when intercepting courses.

Like its neighbor, Century offers a complete line of products, from the simple Century 1, a rate-based, all-electric single-axis system, to the Century 41 flight-director autopilot system. The Century 41 is often found on turboprops. The backbone of the company's product line is the Century 2000, an upgradable system that allows an owner to move from a simple roll autopilot all the way up to a three-axis flight-director system. Although the design is two decades old, the name, at least, seems suddenly relevant as the calendar ticks over to 2000.

Century, too, is busy generating new STCs. When I was there, a Beech 18 dominated the hangar floor as technicians scurried about installing a new system — an STC that doesn't get exercised a lot, mused Don Brooks, Century's technical sales associate. In the shop, craftsmen painstakingly trimmed, filed, and drilled thick aluminum pieces to custom-fit a panel.

For both companies, dealers in the field do the vast majority of installations. However, you get the impression that those done at the respective factories are completed with a careful pride because you know each of the aircraft owners will tell everyone they know that "I had mine installed at the factory."

No matter where your installation was done, it's nice to know that if you find yourself in north Texas, you can taxi right to the factory door for a quick autopilot tune-up — one of the charms of general aviation.

E-mail the author at [email protected].