Though the flight path calculation is fundamental to the internal workings of the SVT display, Garmin also wanted to show the pilot his flight path. The company experimented with various symbols to show flight path but settled on what is the norm in head-up displays, which is a circle with short lines sticking out like stubby wings and a vertical tail. The flight path marker, as Garmin calls it, appears on the display as soon as the airplane is accelerating down the runway and it projects the airplane's path during all phases of flight. The flight path marker will be centered only under steady state flight conditions with no wind. At other times it will be moving around the display showing where the airplane is going, not where the nose is pointed.
Having flight path information makes possible some kind of highway in the sky (HITS) presentation that combines both lateral and vertical guidance in a single symbol. All types of HITS symbols have been experimented with over the years, but the one that NASA and other researchers have found works best for the entire range of pilot experience is a series of boxes in space that you fly through using the flight path marker. The boxes can describe a curved flight path and of course provide guidance vertically.
But Garmin's own testing revealed that the pathways -- as it calls the boxes -- are not ideal for every pilot. The company found that it was impossible to beat the conventional single-cue V-bar flight director when it comes to commanding the desired pitch and roll to stay on the computed course. The V-bar intuitively shows the bank angle and pitch needed to satisfy the command, while it takes some experience to know what kind of maneuvering will move the flight path marker into the boxes. Bottom line, Garmin SVT has the pathway boxes and the conventional flight director, and you can select the boxes on or off.
SVT displays traffic information in a way I haven't seen before. Instead of the normal TCAS diamond symbol with a plus or minus sign in front of a number of hundreds of feet to show relative altitude of the target, SVT presents the threat in 3-D. For example, if the target airplane is in your 10 o'clock position 100 feet above you and moving left to right, that's where the target shows up on the PFD display. The symbol grows in size and changes color as the threat intensifies, but just as with the synthetic view of the terrain, an avoidance maneuver is obvious, requiring no numbers to evaluate. Instead of reading the plus sign and understanding the airplane is above you, and then reading the number of hundreds of feet, with SVT you look at the target, see its relative position and motion instantly, and quickly assess the threat and calculate an escape exactly as you would with actual visual contact.
To see SVT in action Garmin's chief of flight operations Tom Carr and I saddled up in a Cessna 182 that had been used for much of the development and test flying. The wind was howling over 30 knots from the south, so turbulence and lots of big crab angles were going to make the display interesting.
Terrain is displayed on the SVT as soon as the system is aligned. There is a small hill between Garmin's ramp and the runway, and even at taxi speed I could see the terrain was above the zero pitch line and we would not clear it without a hard right turn to follow the pavement. At 30 knots of groundspeed on takeoff roll the SVT shows the runway under you and the flight path marker is active. Terrain near Garmin's Olathe, Kansas, home is pretty flat, but the SVT image has nice texture so it looks much like the real surface beneath you. Gridlines on the terrain help provide distance and height perception, and actually look much like the "section lines" that are common across the broad center of the country.
Tom pointed me at a nearby broadcast tower that is more than 1,000 feet agl and I put the flight path marker on the tower symbol shown on SVT. With the very strong wind the nose was pointed at least 20 degrees left of the tower, both on SVT and visually out the windshield, but the flight path marker showed we were flying directly at the tower. As we neared the obstacle it grew in size on the display. When the TAWS system calculated we were less than 60 seconds from impact, the tower symbol turned yellow. Less than 30 seconds from impact the tower symbol turned red and grew in size to occupy most of the center display area. It took most of my willpower not to turn away from the tower, or climb, before the 30 second warning because the display on SVT is so compelling, and threatening. It would be impossible not to immediately understand the threat and see how to avoid it based on SVT alone without the added TAWS alerts.
I flew very low over one of the big reservoirs in eastern Kansas and was pleased with how the blue water display contrasted with the blue sky presentation. There was no mistaking the color and subtle texture of the water for the normal "blue is up" display of the PFD.
I aimed at the hilly shoreline of the lake and watched as the terrain on SVT turned yellow to show that I was less than 60 seconds from coming too close with my present flight path. Soon the terrain that I would not clear without a flight path change turned red. It was obvious to me just from looking at the SVT image that I was dangerously close to the terrain without the color warnings, but they do provide another level of alerting for a possibly confused or distracted pilot.
