***TOD-Top of Descent***
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How do you determine the top of descent (TOD)? I always use the rule of thumb (altitude-altitude airfield)x3.
But if I then know that I need 80 Mn for the descent, how do I know where that point is?
I can't see in the Flight Management System (FMS) how far it is to the airport. I would have to cumbersomely add the distances of the individual legs. Is that how it works? At any rate, I can't imagine that. -
@fly-harry-fly You could ballpark it using a VOR, but yeah, otherwise you need to do it manually and count back the legs from the waypoint you want to reach it at. This plane is quite manual, and traditionally didn't even have an FMS. All the mod cons are in the RJ series which is the modern update of the 146 that JF is working on as well as an extra.
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@fragron I always forget the Prog page exists, haha. But that gives you the distance to the threshold though, right? You're more likely to want to reach that altitude a few waypoints before that point, which won't be shown on the Prog page until you're well past the point of wanting to descend. Unless you can add fixes or specific waypoints to measure distances too now?
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Prog Page shows trackmiles to "end of flightplan" (minus GA). The rest ist manual calculation. At the beginning i calculated -10 Miles and 3000ft above Airport. Since then i wrote a small "Excel" which calculates Tod and descent rate. But that still leaves stortcuts and restrictions to be ballparked. The reason i dont yet fly the 146 in vatsim, to much stress :zany_face:
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@fly-harry-fly
Descending at 2000ft x minute.
At 31000ft = 31000/2000 = You arrive at altitude ZERO in 15,5 minutes.
Descending at 415kts GS = 415nm/hour, 415/60 minutes = +-7 nm a minute.
7nm x 15,5 minutes = 108nm
The TOD descend at 2000ft a minute at 415kts GS is 108nm away from airport.
Changing the altitude, rate of descent, and speed of descent, will change the distance. -
@fragron
Thanks for the tip. I did not know that you can see the distance in the prog page. Subtracting the STAR is not that complicated. I will try it out soon.But I have now also switched to flying the BAe without the FMS. Only after VOR. This is really fun and also a bit more challenging. With this type of navigation, I have the distance to the last VOR. This is doing quite well.
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There is a simple method which works reasonably well and as a simple soul even I can work these out in my head.
DESCENT POINT - DIVIDE FLIGHT LEVEL BY 3
So FL300 divided by 3 is 100. So you need to start your descent 100 miles from destination.
Keep checking during the descent, so passing 10,000 ft, 100/3 = 33 miles from touchdown.RATE OF DESCENT TO MAINTAIN A 3 DEGREE APPROACH- MULTIPLY GROUNDSPEED BY TEN AND HALVE THE RESULT
Groundspeed is 400 KTS. 400*10=4000. 4000/2 = 2000FT per minute Rate of Descent
You need to recalculate as the aircraft slows down in the descent.
So on final approach GS around 120 KTS. 1200/2 gives you a rate of descent rate of 600 FPM.Hope that helps