Twenty years ago Gulfstream was the first transport jet maker to certify an electronic primary flight display (PFD) that showed all essential flight information on a single screen. And now it has become the first airplane maker to win approval for synthetic vision display on the PFD. Synthetic Vision primary flight display (SV-PFD) was certified as part of the PlaneView avionics in large cabin Gulfstreams late last year.
Synthetic vision is a computer re-creation of the terrain and obstacles ahead of the airplane. The system notes the airplane's GPS-determined position and track, and then looks in a database to find a stored description of the terrain and obstacles ahead. The terrain data is already onboard because it is used by the ground proximity warning system (GPWS) to issue alerts if a pilot strays too low. This data is computer massaged to create a picture of what the actual terrain looks like on the synthetic display.
Synthetic vision (SV) has been flying on light airplanes for several years, and there have been a couple of approvals for retrofit displays in jets that show SV, but Gulfstream is the first transport category airplane maker to develop such a system. And from the beginning the company's focus was to make the SV an integral part of the PFD so that pilots can see terrain features along with all of the conventional information necessary to fly IFR. Gulfstream is in the unique position of having the infrared EVS system that shows an image of the actual terrain, obstructions or objects on a runway on the head-up display (HUD). The EVS is a "real" look through darkness, precip and fog that is good for shorter ranges, while the SVS is a computer-generated picture of what lies ahead and presents the big picture. Both SV and the infrared view of EVS have powerful advantages so you'll want both, not to choose between them.
One of the early hurdles for Gulfstream to overcome on the way to certification of an SV-PFD was to explain to the FAA what it would do, and how it could help. There is nothing in the certification stand-ards that addresses SV-PFD for transport airplanes, and the airlines don't seem particularly interested in the technology, so it was up to Gulfstream to educate the FAA.
The benefits of SV-PFD, or any other moving map, are usually said to be "enhanced situational awareness." Every pilot knows what that means - that you have a better understanding of your present flight situation - but that term doesn't exist in the rules, so it has no certification value at the transport level. What the Gulfstream test pilots did was search the FAA's own literature and found that a joint steering committee "seeks to reduce weather-related accidents through new technology." A study of the accident record showed that up to 91 percent of the fatal general aviation accidents involved bad weather, so SV-PFD could help avoid those. Now the FAA could understand the value.
But how best to show a view of the terrain ahead? The easy way is to show the terrain under the track of the airplane, which is its GPS-computed path over the ground. But that's not what pilots expect to see when they look out the windshield because airplanes do not "track" where they are pointed if there is any wind. And Gulfstream insisted that the synthetic view be as close to the real-world view as possible. Also, Gulfstream's pilots determined from the beginning that the SV-PFD could not require new pilot skills to use, and that conventional symbols and displays be retained so any experienced IFR pilot can understand the picture the first time, and every time.
The only way to accomplish those goals is to present the SV image ahead of the airplane - where it is pointed, not where it is tracking. That way the flight director symbols, compass rose and all other elements of the PFD make sense. And when you break out of the clouds in a left crosswind, for example, the runway will be to the right of the nose, where it has always been and where it was shown on the SV image. If Gulfstream had used the less complicated track-up display, the runway would appear on the SV image to be directly ahead because you are tracking toward it, but in a crab to correct for crosswind, the real runway would be to the side of the nose when you got sight of it, and that can lead to confusion.
But Gulfstream also shows track with a flight path symbol, which you can see moving over the terrain image as the heading points right or left in a crosswind. The flight path symbol also shows your vertical path and whether you're tracking to the runway or above the terrain.
The SV-PFD has the vertical altimeter and airspeed tape displays pushed further away from the center to provide more uncluttered space to show the SV image. The SV image extends out about 35 nm ahead of the Gulfstream's nose, and the resolution of the picture is very good. Hills, valleys, streams, coastlines and other features look realistic. The resolution of the display varies with details stored in the database. Near airports the extra data points allow a horizontal accuracy of about 75 feet, so when you approach a runway, it is in the right place. Where the stored data is more coarse, typical accuracy of a terrain display is one-tenth of a mile or better. Vertical accuracy is better than 75 feet.
To see the SV-PFD in action, Gulfstream test pilot Gary Freeman and I, along with flight test engineer Mike Bauer, fired up a G450 hours before dawn in Savannah. We couldn't count on bad weather to see the system in action, so we had to make sure it was dark to mask the view of the real world outside. There wasn't a lot to see in the flat lowlands around Savannah - though the SV-PFD did show good terrain texture, streams, and of course the runway - so our mission was to fly to Asheville, North Carolina, and practice approaches in that rugged terrain.
The only adjustment I had to make initially to the new display was on takeoff rotation where the target pitch attitude caused the display to "scroll" up, the same way a HUD does. But the familiar V-bar flight director gave its rotation pitch command just as it does on a conventional PFD, so the familiar was there all along. Pilots can select either a single-cue V-bar, cross pointer or HUD-style flight path command indicators on the new display.
