# A320 – TOD Calculator Added to the FlyByWire Tablet

This is the top of descent calculator that is now coming to be implemented in the fly by wire tablet. Just before we go in and have a look at it, what i want to stress very severely is that this is not working v nav. It has absolutely no control over the autopilot. It adds nothing to the flight management computer. It doesn’t create a descent profile of any kind. It doesn’t initiate your descent for you. It adds nothing to the navigation display, but it is a fantastic tool to help you as a pilot, calculate your top of descent and how to perform the descent so let’s go in and take a look. Shall we so here is the flyby wire tablet, which many of you are now already familiar with? So if we come across here and select tools, here is our brand new top of descent calculator and i get asked all the time. How do i know when to start the top of descent and up until now, i’ve been using a general rule of thumb um to work that out, whilst we’ve not got working v nav, but now i will start using this top of descent calculator. So let’s go in and have a look at how it works. So at the moment you can see it is getting our current ground speed from the simulator 431 knots 431 knots on the ground speed just there, so that matches up as it should.

So how we’re going to use this then to decide? When do we need to start our topic? Descent. Well, it’s got lots of different options that we can use and that’s great for us, because we can manipulate this in the way we need to for any particular flight. So, whether you’re flying on vatsim and say you need to be level at such and such by uh such and such a waypoint um or, if you’re, just flying on your own. And you can target an altitude for your airport, which is what we’re going to look at now now. This is a very crude demonstration here, because i’ve got a target altitude of zero set there, so not very realistic, but just to show you how that would work. So we’re, currently at thirty thousand feet, and if i wanted to target an altitude of zero so getting to the airport um, then our distance, vertical speed or angle fields can be populated here so let’s say we wanted to start our descent 100 miles away. What it would then do is it would tell us that, at this current speed at 30 000 feet to be at zero feet by the time you’ve traveled 100 miles. You need to descend at an altitude. You need to descend at a rate rather of 1853 feet per minute or at a descent angle of minus 2.8 degrees. Okay, so let’s clear that if we want to choose our own vertical speed for the descent, so maybe a nice relaxing, steady, slower descent of 1400 feet per minute when that field becomes populated, it tells us well.

In that case, you need to start your descent about 132 miles before the target. We can also clear that we can also and choose our own descent angle. So if we decided to descend at about three degrees, we would need to start the descent 94 miles away from the target. Remember if you’re going to use a degrees for your descent, then you need to come over here and change from heading and vs speed to track and fpa speed. Okay, so let’s just come back over here and and clear that now realistically, we wouldn’t target an altitude of zero because that’s not how we would do an approach. Ordinarily, what we would look to do is we would have our navigraft charts and we would be targeting. Maybe a specific waypoint rather than the final airport itself um. So if we just come down here and have a look at our navigation computer we’re, currently on approach here to belfast we’re, currently 208 miles away from belfast and if we scroll up, if you don’t, have access to any sort of navigation charts or anything like that. You will see that microsoft, flight simulator does put in constraints so there’s a constraint here as we get towards the belfast vor there’s a constraint there of 2500 feet, so that would be a better altitude to try and target. So we can pop that in here 2500 feet and again you can choose how far away you would like to start that descent or if you wanted to select a nice descent rate again about 1500 feet per minute.

That is a very nice slow, steady descent. So it now tells us that we need to start that about 160 miles away before the target. Well, that’s, fine, but how do we know when we’re 116 miles away from the belfast vor? Unfortunately, at the moment, the flight plan in the mcdo does not show us that information, so we have to use a sort of other workaround for that, and that is the use of the range rings here on the navigation display. Now the range rings can be changed up here, so at the moment i’ve got it set out to the furthest, but you can obviously bring that in like so, and all we’re going to do is just double check that again so about 160 miles away from the Belfast vor, which, if we have a quick look and zoom in, is actually in the middle of all this uh all of these waypoints just here as i actually bring that in maybe one more, you can see that there will obviously then more spread out here on The navigation display, as you zoom in so when you see the belfast waypoint, started to appear at 160 miles, so you can close to 120 dashed line around here. That is when you would need to start your descent at a rate of 1500 feet per minute. All right, so that is a great way of looking at that another way of doing it is, of course, if you’re planning an ils approach.

Most of the time you want to be, if it’s, normal, standardised approach, three degree, angle, etc. Normally, you want to be aiming for an altitude of about 3 000 feet when you’re twenty mile fifteen to twenty miles away from uh capturing the ils uh. That ensures, then that you capture the glide slope from below, rather than trying to chase it all the way down. So if we wanted to be at 3 000 feet by the time, we are 20 miles away from the airport, we could then do this. So thirty thousand feet: we want to target three thousand feet and still gon na use that descent rate you know what actually we could probably increase that descent rate a little bit so slightly more realistic descent, a vertical speed of 1 800 feet per minute, so that Is telling us we would want to start our descent about 95 miles before the target? Well, if we want them to ensure that when we’re 20 miles away from the airport, we are at 30 000 feet. What we can use is the distance that we have just here, because the distance down here this is the distance from the actual airport belfast airport, so currently 184 miles away from that, so 3000 feet 20 miles away from the airport. That would be 95 plus 20. So 115, when this then says 150 miles away from belfast, that is when we would start to initiate descent, and that would get us to 3 000 feet when we are 30 miles away from belfast at the moment.

Of course, what you can also change? Oh little stutter in the simulator there, what you can also change is the ground speed. So at the moment this is getting its information from the from the aircraft, so 246 knots on the ground. Speed, if you know, or you get a speed restriction that you’re going to be slowing down well, then you can go to the manual input to change that. So at the moment, 95 miles go to a manual input. Just remove that last one there. If we want to add 3000 feet and a ground speed of uh, let’s, say 350., so now it’s going to tell us, we need to start our descent at about one at about 88 miles away. That would get us 3000 feet so 88 miles plus 20 would give you the top of the cent calculation to ensure that you’re 3000 feet 20 miles away from your uh from your airport to intercept your ils. Now this target altitude – i do have to stress the target altitude – is barometric pressure altitude. It is not radio altimeter, so just to make sure we understand the two i’ve said: we’re going to target an altitude of 3000 feet here, well, that’s, all well and good, but if the airport that you’re landing at is actually at an elevation of 2000 feet above Sea level you’re only going to be 1 000 feet above the airport when you reach this altitude so again, that’s where knowing the elevation of the airport is very, very important.

So if you are able to get charts to double check that then it’s always a good idea, but a strict rule of thumb. You want to be 3000 feet above the airport elevation for uh, starting your ils approach when you’re about 15 to 20 miles away. So don’t confuse both the barometric and the radio altimeter, as both can have disastrous consequences if you get them mixed up. For example, if you were flying into innsbruck, for example, which is obviously quite high up so hopefully that’s giving you a little insight into how we can use the brand new topics calculator at the time of filming this video, this is still in test phases. So please don’t contact flyby and ask them. Why is that not yet working as soon as it’s released properly um i’ll update the video information so you’ll be able to see that? But for now, just another great big shout out to the 5ry team for giving us another piece of really useful technology that we can use in microsoft, financing 2020 to add some more realism to the way we the way we work i’ll certainly be using this tool. In my upcoming streams, if you have any questions, please do uh comment down on the video below give the fly by wire, guys a thumbs up and like the stream and video. For me, that will be great and i look forward to using this brand new feature in upcoming videos thanks very much guys for watching.