On a cold and blustery Sunday night last month the high-pitched whine of a Gulfstream G450 cut the air above Vermont’s Mount Snow ski resort. The sound must have surprised anyone who heard it. After all, this wasn’t Aspen or Jackson Hole. Mount Snow Airport’s tiny 2,650-foot north-south runway is far too short to accommodate a 70,000-pound business jet; the occasional light piston twin is about the biggest airplane residents are used to hearing or seeing overhead. And when 35-knot crosswinds and blowing snow are buffeting the field, the approach always
remains dark and silent.

But this particular airplane, one of the first to be fitted with Gulfstream’s just-certified synthetic-vision primary flight display (SV-PFD), wasn’t there to pick up some snowbound company chief executive and his family after a weekend ski holiday. Rather, it was a chance to show the media the production version of a technology that Gulfstream and Honeywell test pilots have been honing for the last two years–a high-tech journey, to be sure, and one that is culminating with the introduction of SV-PFD in Gulfstream’s top models spanning the G350/450/500/550.

Gulfstream in late January received FAA certification for the software and hardware modification, making it the first OEM to gain such approval in a Part 25 production airplane. The award also included Gulfstream’s second-generation infrared enhanced-vision system, known as EVS II. The company will integrate both technologies into the production line this spring. It estimates the optional SV-PFD upgrade will be priced at about $300,000 in new airplanes rolling out of its Savannah, Ga. factory and offered for a similar price to operators of in-service models flying with Honeywell PlaneView avionics.

Engineers have studied SVS concepts for several years, but the joint Gulfstream-Honeywell test program accelerated once the project was given the green light in July 2006. Honeywell engineers used rapid prototyping tools to develop a synthetic-vision system for Gulfstream that provides all of the benefits the manufacturer’s test pilots said they wanted and none of the distractions they felt were included in some early SVS designs. “We were on the same page through the whole process,” said Gulfstream SVS project test pilot Tom Horn of his counterparts at Honeywell. “It’s amazing how well our ideas meshed.”

In the final version, 3-D hills, mountains, obstacles and water are displayed in sectional-chart-like colors using six-arc-second terrain data culled directly from the airplane’s enhanced ground proximity warning system (EGPWS). That means the visual scene for the entire planet is recreated in 600- by 600-foot boxes, with graphics-processing techniques used to smooth terrain contours for a natural-looking presentation. Beyond 12 nm the scene is presented using 12-arc-second squares (1,200 by 1,200 feet) and the graphics computer seamlessly stitches the boundary between the two areas.

Early in the program, Gulfstream and Honeywell decided that highway-in-the-sky type guidance cues or TCAS symbology presented on the SV-PFD would be too distracting. Designers also opted not to show EGPWS terrain warnings on the SVS display in red and yellow, primarily due to certification hurdles that arose during development. In all, pilots spent more than 600 hours in the air with SV-PFD and another 1,000 hours in the simulator, bringing to a successful conclusion a technology initiative that for Honeywell started nearly 10 years ago and included input from engineers at several of its aerospace and human-factors groups.

During last month’s media demonstration flight, Honeywell chief pilot Ronald Weight flew in the left seat of the company’s corporate G450 while senior experimental test pilot Jary Engles handled right-seat duties and occasionally attempted to steady a journalist’s point-and-shoot camera, a task made difficult by the moderate to occasionally strong turbulence over southern Vermont. The airplane departed Morristown Municipal Airport in New Jersey, where Honeywell’s flight department is based, for the journey north and included low approaches to Mount Snow and Rutland Regional Airport. (The photos accompanying this article are rare examples of pictures from the flight that turned out sharp enough to print.)
Flying in ‘Heading-plus’ Mode

The normal SVS layout features a wide zero-pitch reference line flanked by transparent airspeed and altitude tapes. A flight-path marker and speed chevron on the display mimic the symbology that’s shown on the HUD, with an additional v-shaped marker always showing where the nose is pointed. A bumpy, 54-knot crosswind on the Rnav approach to Mount Snow’s Runway 1 was more than adequate to demonstrate one of the more noteworthy advanced features of SV-PFD, called heading-plus mode. When crosswinds are strong, the display automatically reverts to this mode, whereby the visual scene shifts to the left or right by as much as 40 degrees so that the divergent flight-path marker and an inverted v marker are always shown on the display together.

“We actually shift the world to keep the flight-path marker conformal to the view outside,” explained Horn. The technique lets the pilots always see the runway as well as where the nose is really pointed, even when there is a wide disagreement between the two. It’s a hard concept to visualize without actually seeing it demonstrated in the real airplane or a simulator, but once the shifted scene is presented on the display on a real flight it is quite easy for the pilot to interpret the information. One of the biggest benefits the shifted scene provides is letting the pilots know exactly where they should be looking for the runway when they break out of the clouds.

Another helpful feature of the Gulfstream SVS display is a cyan-colored breadcrumb trail that follows an extended runway center line out to a distance of 15 nm. The runway itself is shown inside a cyan box, making it readily apparent to the pilots which approach is dialed into the FMS. The EGPWS database includes information on more than 30,000 runways at 8,600 airports around the world. If an airport isn’t included in the database, the PFD reverts to a traditional blue-over-brown ADI and pilots fly the approach without the assistance of synthetic visual cues.

“The EGPWS and SVS database are one and the same,” noted Sergio Cecutta, Honeywell marketing manager for advanced systems. “Ours is a high-integrity database that also includes more than 100,000 obstacles and most bodies of water. All of it can be presented on the SV-PFD display in 3-D. Basically, the world is a big grid” made up of data points.

All of the additional information that is supplied by the SV-PFD view is presented elsewhere in the cockpit, Horn noted. Flight-guidance information is shown on the HUD, for example, and terrain information can be viewed on the EGPWS display–although not as intuitively as when viewing the video-game-like scene of the world ahead on the SV display. For this reason, said Horn, differences training isn’t required of crews transitioning from the basic PlaneView cockpit to SV-PFD.
Gulfstream has prepared a 20-minute online video to familiarize pilots with the technology, but they won’t be quizzed by their FlightSafety instructor or otherwise need to demonstrate special proficiency using the system. “That’s why we call it SV-PFD,” Horn said. “We’re simply adding information to the existing primary flight display.”

While testing the system over the course of the last year-and-a-half, Gulfstream test pilots flew SV-PFD approaches into some of the most challenging airports they could find, including Aspen, Colo.; Jackson Hole, Wyo.; Reno, Nev.; Hot Springs, Ark., and Nashua, N.H. On one flight, Horn noted, he and his copilot flew approaches
to 16 different airports without touching down. Test pilots also spent a great deal of time testing unusual attitudes, whereby the 3-D visual scene automatically disappears and is replaced with a traditional ADI and essential flight information. The system will also revert to ADI mode in the event that EPU (estimated position uncertainty) parameters go out of tolerance, Horn noted.

Primarily a software upgrade, SV-PFD also involves replacing the mode controller above the displays and graphics card. The modification should take only a day to complete, Horn said. Gulfstream has started an in-service evaluation of SV-PFD with a small group of operators. Pilots will be asked to fill out forms after each flight, information from which could lead to changes in future SV-PFD software revisions. Horn said Gulfstream hopes to make SV-PFD available to all operators once about 500 hours of flight evaluations have been completed.