Over the years, I have had the opportunity to look at developmental Synthetic Vision systems in various simulators, and have always felt that the technology was very promising. Unfortunately, I have not had a chance to spend any time with them in the "real world" until recently. As we all know things can be very different between simulations and the real world, so I have been anxious to see how the tools play when the chips are down, and have real value. Now that I have a system in my airplane, I am finding that the promises are being fulfilled, but that there is also a non-trivial learning curve involved - like with any new technology in the cockpit, pilots have to learn how to use it and what kind of limitations it has. Our recent trip to the mountains of Southern California gave me an opportunity to start my way up the learning curve, and I can share a few observations. These notes apply specifically to the first release of the Grand Rapids Technology HX with Synthetic Vision. In this release, terrain is displayed, but there are no runways, roads, or other manmade landmarks depicted.
1) Probably the most difficult thing to try and get out of the SV depiction of terrain is how far away you are from it. When you look out the window at the real world, you see features such as trees, roads, and buildings that give you an intuitive sense of how high you are. Without these cues, even though the virtual terrain is accurately reproduced from elevation data, it is very hard to see if you are about to skim the surface, or if you are safely 1,000 above it. Flying into a wide mountain valley, you can see the peaks on either side, but it is hard to tell if you are descending into the terrain in the middle. I was approaching Big Bear Lake at night, and to be honest, I was really glad when I picked up the lights of the town and the runway, because this gave me a much better feeling for ground clearance than I got from the SV (at first). After seeing the relationship of the SV view and that of the real world out the window, this uncertainty lessened, but there is a definite amount of learning that your mind has to go through to get the correlation.
2) Probably one of the most important features of the SV display is the "horizon line", something I really didn't think would matter at first. This line shows where the earth's horizon would be if you could see it (through clouds or terrain that is in the way). You need to use this line to help your mind understand if the terrain that is depicted on the SV display is higher or lower than your present position - anything above the line is higher, anything that is below the line should pass under you if you are in level flight. It is important to couple the horizon line with the velocity vector - in the case of the GRT, a little circle with stub wings and tail - that shows exactly where you are headed. If this is in the sky, then you should clear the terrain. If it is pointed at terrain, you will eventually hit the ground. Of course, it's height above or below the horizon line tells if you are climbing or descending. It is important to correlate all three things - SV terrain, Horizon line, and Velocity Vector - in order to truly figure out if you are going to clear or impact terrain.
3) Doing an approach into an airport at night in the mountains, the terrain was neat to have, but what really made me feel comfortable was the artificial glide slope guidance - in the case of the GRT, this is provided via the Highway in the Sky. There simply is not enough depth detail in the SV to give you the same visual cues that you get when you fly "out the window", so some form of guidance is necessary. The HITS display gives you this reference, and a measure of understanding of where you are relative to your intended path. Perhaps when the runways get added to the display, this will become less important, but I found the HITS path to be very important when I descended below 1,000' AGL at night. Interestingly enough, the best intuitive guidance comes when you get low enough that the HITS "squares" start touching the terrain ahead. The bottom half of the squares end up beneath the surface, and are therefore hidden. The point where the sides touch the ground actually then give you a very strong visual cue for how high you are - this is perhaps a clue as to how our minds interpret the terrain clearance picture - we need to see something that represents exactly where the terrain is out in front of us, and the featureless shades don't do this as well as we'd like.
4) So, if I feel that I need some sort of guidance lines (other than just seeing the terrain), what good is the Synthetic Vision? Why not just have geometric guidance the way we have had up until now? Well, that's a good question. First, I think the we have to remember that the current state of the art in SV representations of terrain are works in progress. More detail will soon be added that will give us a better intuitive sense of height and motion. Second, the SV gives us a great overall situational awareness vision - we know that if we turn off the path, we'll have a mountain or hill over there that is higher than we are. This is extremely valuable, and the more I watch the videos of the work I did in the mountains, the clearer the value becomes. In fact, that is really th whole point ? there is a learning curve! You can?t expect to go out and use this tool in bad weaetrh or at night without first getting used to what it is telling you ? but once you do that, the benefits really begin to stand out.
The following video shows an approach to Big Bear Lake (L35) in California. The approach was flown at night, the data recorded, and then video?d off the screen in playback mode on the ground (which is why there is some semblance of smoothness!) - Enjoy!
http://www.youtube.com/watch?v=H8SID85-BQk
Paul
1) Probably the most difficult thing to try and get out of the SV depiction of terrain is how far away you are from it. When you look out the window at the real world, you see features such as trees, roads, and buildings that give you an intuitive sense of how high you are. Without these cues, even though the virtual terrain is accurately reproduced from elevation data, it is very hard to see if you are about to skim the surface, or if you are safely 1,000 above it. Flying into a wide mountain valley, you can see the peaks on either side, but it is hard to tell if you are descending into the terrain in the middle. I was approaching Big Bear Lake at night, and to be honest, I was really glad when I picked up the lights of the town and the runway, because this gave me a much better feeling for ground clearance than I got from the SV (at first). After seeing the relationship of the SV view and that of the real world out the window, this uncertainty lessened, but there is a definite amount of learning that your mind has to go through to get the correlation.
2) Probably one of the most important features of the SV display is the "horizon line", something I really didn't think would matter at first. This line shows where the earth's horizon would be if you could see it (through clouds or terrain that is in the way). You need to use this line to help your mind understand if the terrain that is depicted on the SV display is higher or lower than your present position - anything above the line is higher, anything that is below the line should pass under you if you are in level flight. It is important to couple the horizon line with the velocity vector - in the case of the GRT, a little circle with stub wings and tail - that shows exactly where you are headed. If this is in the sky, then you should clear the terrain. If it is pointed at terrain, you will eventually hit the ground. Of course, it's height above or below the horizon line tells if you are climbing or descending. It is important to correlate all three things - SV terrain, Horizon line, and Velocity Vector - in order to truly figure out if you are going to clear or impact terrain.
3) Doing an approach into an airport at night in the mountains, the terrain was neat to have, but what really made me feel comfortable was the artificial glide slope guidance - in the case of the GRT, this is provided via the Highway in the Sky. There simply is not enough depth detail in the SV to give you the same visual cues that you get when you fly "out the window", so some form of guidance is necessary. The HITS display gives you this reference, and a measure of understanding of where you are relative to your intended path. Perhaps when the runways get added to the display, this will become less important, but I found the HITS path to be very important when I descended below 1,000' AGL at night. Interestingly enough, the best intuitive guidance comes when you get low enough that the HITS "squares" start touching the terrain ahead. The bottom half of the squares end up beneath the surface, and are therefore hidden. The point where the sides touch the ground actually then give you a very strong visual cue for how high you are - this is perhaps a clue as to how our minds interpret the terrain clearance picture - we need to see something that represents exactly where the terrain is out in front of us, and the featureless shades don't do this as well as we'd like.
4) So, if I feel that I need some sort of guidance lines (other than just seeing the terrain), what good is the Synthetic Vision? Why not just have geometric guidance the way we have had up until now? Well, that's a good question. First, I think the we have to remember that the current state of the art in SV representations of terrain are works in progress. More detail will soon be added that will give us a better intuitive sense of height and motion. Second, the SV gives us a great overall situational awareness vision - we know that if we turn off the path, we'll have a mountain or hill over there that is higher than we are. This is extremely valuable, and the more I watch the videos of the work I did in the mountains, the clearer the value becomes. In fact, that is really th whole point ? there is a learning curve! You can?t expect to go out and use this tool in bad weaetrh or at night without first getting used to what it is telling you ? but once you do that, the benefits really begin to stand out.
The following video shows an approach to Big Bear Lake (L35) in California. The approach was flown at night, the data recorded, and then video?d off the screen in playback mode on the ground (which is why there is some semblance of smoothness!) - Enjoy!
http://www.youtube.com/watch?v=H8SID85-BQk
Paul
