Pilot Products

S-Tec GPSS

S-Tec Corporation used EAA AirVenture '99 in Oshkosh to launch two new autopilots and a new product that will pique the interest of many airplane owners, especially those who already own S-Tec autopilots and a high-end GPS receiver.

Continuing the company's tradition of not orphaning its current stable of owners, S-Tec introduced GPSS, or GPS Steering, which allows the company's new and existing lines of autopilots to receive roll-steering commands from many panel-mounted GPS units. For example, most Garmins, the Bendix/King KLN 90B, and the UPS Aviation Technologies (formerly II Morrow) 2001 output roll-steering commands to feed any S-Tec autopilot with built-in roll steering or one with an optional roll-steering converter.

Roll steering allows the autopilot to accept ARINC 429 digital composite steering commands directly from the GPS rather than analog left/right error signals from a course deviation indicator (CDI) or horizontal situation indicator (HSI). Since the GPS is talking directly to the autopilot, information such as groundspeed and track are factored into the autopilot's flying skills. Steering commands come at a point where the autopilot can make centerline-to-centerline transitions along a route in the GPS's flight plan. This function is known as turn anticipation. The overall effect is a seamless transition from one course to the next without the pilot's having to change the CDI. Since the autopilot is talking directly to the GPS, it ignores what the CDI shows.

Roll steering has been around for decades in Transport-category airplanes but an affordable version for general aviation simply has not existed. Bendix/King's KFC 225 (see "Pilot Products," June Pilot) is a high-end, attitude-based autopilot with roll-steering capability but, at a starting price of nearly $30,000, it is geared toward the high-end GA market. S-Tec believes that at $695 for its GPSS conversion module, affordable roll steering is now available to the masses.

AOPA Pilot was invited to S-Tec's Mineral Wells, Texas, facility to see first-hand what GPSS does to S-Tec autopilots. Our testbed was a Beech A36 Bonanza equipped with a new S-Tec System Fifty X, the two-axis version of the company's new autopilot line with built-in GPSS. (The single-axis version is the System Forty X.) Both are radio stack-mounted units similar to the company's System 55. In this airplane, the Fifty X took GPSS commands from a Garmin GNS 430 GPS/navcom. After takeoff, the autopilot was activated to fly a flight-planned course to a nearby airport. To activate GPSS, you must punch the Nav key on the autopilot twice. Pushing once activates only the standard CDI-based Nav mode.

Our flight plan terminated at a DME fix that doubles as an initial approach fix to the VOR/DME-A approach at Cleburne (Texas) Municipal Airport. The fix marked the beginning of a DME arc transition to the inbound course on the approach. By the time that I figured out the math required to plan our intercept to the arc based on our groundspeed, the autopilot had already begun the turn. We just sat back and watched as the GPS told the autopilot when to begin the nearly 110-degree turn to intercept the arc transition. Once established on the arc, the autopilot kept a smooth and steady 2-degree bank to hold the arc perfectly based on our constantly changing groundspeed — the arc was flown far smoother than any human could manage.

We purposely neglected changing the omnibearing selector (OBS) as we rounded the arc to see firsthand that GPSS cares not what the CDI says. Again we watched as the autopilot anticipated the turn to the inbound course and led the airplane into it perfectly. Watching it all unfold on the Garmin's moving map left no doubt as to our position in relation to the airport. All that was left was to control the vertical element of the flight.

Ironically, during a subsequent approach the airplane's compass system failed, locking the HSI's rotating card. Even in the Free mode, the HSI refused to budge. Being newly exposed to the technology, we weren't quite sure how this would affect the demonstration. We quickly realized that a failure of the compass system had no effect whatsoever on the communications between the autopilot and the GPS. In a partial-panel emergency, an S-Tec autopilot equipped with GPSS could bail the pilot out of a heap of trouble. Remember that S-Tec autopilots are rate-based, so a vacuum system failure does not affect autopilot operations. With GPSS, the pilot could fly a nonprecision approach without having to use a watch and a whiskey compass to time turns.

Another benefit of GPSS is superior wind-correction ability. When fighting a fierce crosswind with the Nav mode engaged, current autopilots initially turn to the course that's dialed into the CDI, sailing the airplane way off course when winds are really whipping. Over the course of several minutes, the CDI tells the autopilot that it needs to dial in a wind correction in very small increments. By the time the autopilot gets back on course (and it may never get back in the case of strong crosswinds) you'll have wasted time and fuel. With GPSS, this situation should not happen because the CDI is taken out of the loop. It only knows the track error between the bearing to the station and your ground track.

As GPS databases become more and more detailed, including such things as procedure turns and holding patterns, roll steering could essentially fly the entire horizontal aspect of an approach procedure. Basically, if the course is in the GPS database, GPSS will fly it. For now, however, unpublished procedure turns and holding patterns must be flown using the heading bug.

GPSS can be added to any existing S-Tec autopilot at any time. In fact, the company prides itself on its building-block approach to budget-minded autopilot shoppers. An owner could buy a basic single-axis autopilot and eventually upgrade it to a three-axis system with GPSS and nav coupler without having to constantly tear into the airplane to change existing servos and other components as upgrades are made.

GPSS roll-steering capability raises the ante of GA autopilots to the next level. Making it affordable for owners of new and existing S-Tec models is the polish on the spinner. For more information, contact S-Tec Corporation, One S-Tec Way, Municipal Airport, Mineral Wells, Texas, 76067; telephone 940/325-9406 or visit the Web site ( www.s-tec.com). — Peter A. Bedell

Ryan International has introduced its Ryan 9900BX TCAD (traffic alert and collision avoidance device), an active-interrogation system that will allow for coverage in both radar and nonradar environments. The 9900BX has a useful range of 10 miles, which will allow a 30-second warning at a closure rate of 1,200 kt. The active enhancement can be retrofitted to all existing 9900, 9900A, and 9900B models. As a standalone system, the 9900BX lists for $20,200. For more information, contact Ryan International at 614/885-3303, or visit the Web site ( www.ryantcad.com). — PAB

Briefly Noted

Sporty's now offers a Garmin handheld-GPS mount for older Beech airplanes that are equipped with the center-column yoke. The $85 mount, which is made of anodized aluminum, holds Garmin models 89, 90, 92, and 195. To order, call 800/SPORTYS. — PAB

Global Assistive Devices of Fort Lauderdale, Florida, has introduced its latest version of its vibrating watch, the VibraLite 3. Originally designed for the deaf and hard of hearing, pilots soon latched on to VibraLite's benefits in the cockpit, most notably its ability to vibrate the pilot's wrist to remind him or her to switch fuel tanks. The family-owned company took suggestions from pilots to create this latest version of the vibrating watch. Among the changes are two clocks so that one can be set to Zulu time, a repeatable timer that automatically reloads your preset countdown time, a seconds display for more precise timing of instrument approaches, and an auto-on light that can be set to turn on automatically when the watch is tilted for viewing. List price is $49.95. For more information, contact Global Assistive Devices at 888/778-4237 or visit the Web site ( www.globalassistive.com). — PAB

A German watchmaker, Tutima, has introduced the Tutima GMT 24-hour watch. The GMT features a second hour hand that can be set to any time zone for quick deciphering of your home time zone, for example. The watch comes in two sizes, has an optional crystal back, and starts at $950. For more information, call 888/462-8721, or visit the Web site ( www.tutima.com). — PAB

Anyone planning a trip north — way north — to the Canadian High Arctic or Alaska should check out David Rogers' Flying Adventures CD-ROM series (below). Volume one allows the user to follow Rogers and his travel buddy Bill Morris in Morris' Cessna 182 from Maryland to Alert, Northwestern Territories, Canada, which lies at 82.5 degrees north latitude. The CD-ROM also follows the pair's trip to Alaska via Edmonton, Alberta, and the Alaska Highway. The disc contains more than 200 photos, a travel log, chart segments, and other useful information and valuable tips for anyone who is interested in or who would like to fly a small airplane to these exotic locales. Volume two follows Rogers and Morris across the North Atlantic in the 182 and documents a trip down south to the Caribbean. Flying Adventures CD-ROMs list for $29.95 each, or as a set for $54.95. An Internet browser such as Netscape 2.0 or better, or Microsoft's Internet Explorer, is required to view. To order, call NAR Publishing at 1-888-6 FLYADV or 410/349-9094, or visit the Web site ( www.nar-associates.com). — PAB

Unless otherwise stated, products listed herein have not been evaluated by AOPA Pilot editors. AOPA assumes no responsibility for products or services listed or for claims or actions by manufacturers or vendors. However, members unable to get satisfaction regarding products listed should advise AOPA. To submit products for evaluation, contact: New Products Editor, AOPA Pilot, 421 Aviation Way, Frederick, Maryland 21701; telephone 301/695-2350. Links to all Web sites referenced in this issue can be found on AOPA Online ( www.aopa.org/pilot/links/links9909.shtml).