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SVS: Another Safety First for Gulfstream

SVS: Another Safety First for Gulfstream

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.

The Gulfstream test pilot corps examined many highway in the sky (HITS) symbols that are popular on SV for light airplanes, but didn´t like any of them. Their conclusion, and I agree, is that for experienced pilots the HITS symbols — often boxes you fly the airplane through — were more confusing and distracting than the conventional flight director symbols that every Gulfstream pilot already has thousands of hours of experience with. Again, the primary goal of the new system was to add new and helpful information, not force pilots to learn to use or understand new symbols and techniques.

As we climbed, the winds built to more than 65 knots, almost directly off the left wing, and the SV-PFD went into "heading plus" mode. The crab angle to track the course to Asheville was 11 degrees, so our heading was that far left of the track shown by the flight path symbol. That´s too much to fit on the display, so Gulfstream developed a "heading plus" mode where the flight path marker moves out to the edge, and a small triangle appears on the horizon line showing you the actual crab angle, 11 degrees in this situation. This mode is unique to Gulfstream and is one of many problems it solved to show heading up on the SV image, while still making sense of track.

As we cruised along, terrain features below and ahead were apparent. Runways show up in their actual orientation and relative length, though they are greatly expanded so you can see them. Same for obstructions. A 1,000-foot-high tower would not be visible from 41,000 feet if it was shown in actual scale to the other terrain, so it, too, is expanded.

As we neared Asheville, Gary entered the ILS approach to Runway 34 into the flight management system, and a blue dotted line appeared over the extended centerline of the runway. Gulfstream guys call the dots the "breadcrumbs," and it´s a good description, and the significance is instantly apparent. The breadcrumb trail rises and falls over the 3-D SV image, showing you instantly the presence of hills and valleys along the approach as it leads you to the runway.

I intercepted the ILS, followed the flight director commands in the normal way and noticed how the flight path indicator settled down over the breadcrumb trail to the runway. There are significant mountains ahead and on both sides of the approach, and their presence, and relative height and distance away, was immediately apparent. The white horizon line that extends across the display showed the actual horizon with terrain rising above it. Little of the high terrain was visible with the naked eye because it was dark, and there are few inhabitants and thus few lights. But the SV image made it perfectly clear I was descending into a valley with high terrain at the end and on both sides. If I follow the ILS path and fly the missed approach correctly, I will miss all of the terrain with no need to see it. But we humans are best at digesting analog inputs. Flying a number on an approach chart assured terrain clearance, but seeing the terrain all of the time in all conditions is supremely easier to do and would be a backup to any human error in reading and understanding the numbers on the chart.

I also had the HUD down and, on short final, was looking at the infrared EVS image of the actual airport and runway environment. Gary had the same display called up on one of several of the PlaneView flat-panel screens. We could see another airplane taxiing parallel to the runway, could have seen if he had entered the runway or if there had been any other runway obstruction. I leveled off and flew down the runway at about 50 feet before commencing the go-around, and all important details of the darkened airport were visible on the EVS HUD display.

When making the right turn over the lower of the terrain it was easy to see we would clear it on the SVS. Because the terrain data grid does not have enough resolution to define every peak, the system rounds off some at their highest elevation, but after the sun came up, I could visually compare the actual mountains with the computer image, and the computer is very close.

Approach control and the tower were still closed for the night at Asheville, so we vectored ourselves for a few more approaches. Seeing the terrain and the breadcrumb trail to the runway was more reassuring and intuitive than simply intercepting an extended line like we do on a conventional moving map. It was like flying perpetual VFR, but with very precise guidance in several forms.

After the sun came up we flew at a very tall broadcast tower on a hilltop just west of Asheville, and the SV-PFD showed a very unmistakable image of the tower growing as we approached. Gary urged me to wait until the GPWS yelled its "pull up, pull up" command, but it was almost impossible to do. The size of the tower on the SVS display was so compelling that I wanted to turn or climb long before the 30-second warning was issued by the GPWS. That was convincing evidence that GPWS can save you at the last minute, but with the SV-PFD there won´t be a last minute crisis to avoid because you see the terrain or obstruction coming for miles. It was the same when we flew at actual mountains. The GPWS eventually issued its warning and showed red blobs to indicate the presence of threatening terrain, but I had been looking at an accurate picture of those mountains for a long time before and would never have gone as close as the GPWS allows. With SV-PFD and EVS, only a moron would get within 30 seconds of hitting terrain or an obstruction.

Even on the arrival back at the flat land around Savannah the SV-PFD proved to be valuable. The active runway was 9, with the sun low in the east and some haze. We were on a 90-degree base leg cleared for the visual. It was hard to make out the runway staring into the sun, but I could clearly see it in SV, and the breadcrumb trail of final approach. A smooth intercept of final with no overshoot and a stabilized last couple of miles to the runway was a piece of cake to fly.

SV-PFD installations in the large cabin Gulfstreams began early this year. The target is to have the first seven airplanes — including company demonstrators and other high-time operators — accumulate 500 hours of total experience with the system by the end of March. If no issues are identified, full deployment will be available to all operators in the second quarter of the year. SV-PFD adds about 0,000 to the price of the airplane. The system will be available to existing airplanes with software changes and new display controller units. Gulfstream pilots developed the look and operational specifications of SV-PFD, and Honeywell supplies the actual hardware and software.

EVS II will be installed in new airplanes as part of the upgrade, and it uses a new Kollsman infrared camera that requires no external cooling and is supported by much more compact and lighter electronics that save 22 pounds of installed weight. The new camera has 1.6 times increased sensitivity, and computer processing power is four times greater than the original EVS system that was first certified in 2001. With EVS, Gulfstream crews can fly a standard ILS approach down to normal decision height and then continue down to 100 feet above the runway with only the EVS view of the approach or runway lights. At the 100-foot point the real world must be in view, but since the EVS camera is showing the "real" lights and runway surface on the HUD, the transition is seamless.

Synthetic vision won´t reduce minimums beyond what the companion EVS system already provides, but it will show Gulfstream pilots where they are, where the terrain is and where the runway is located before EVS gives its view of the final approach. SV-PFD and EVS adds critical safety information without forcing pilots to learn new techniques or discard decades worth of experience.

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