Using VNAV depends on the kind of FMS you have, and company approval for using some/all of it's features. On the humble ARJ, we can't use VNAV as we have no approval for its use; even though 5 of the fleet have the GNLU FMS kit (GNLU can accept ALT/SPD constraints), which is roughly similiar to a 737NG.
FL260 by Margo
FL180 10d before ESKDO?(I think this is a new one? Our plates have changed)
FL160 at SLP (defined by TLA 10d)
7000' at TWEED (the old plate used to say " 7000' or FL Equivalent" again this may have changed)
Generally if you check with ATC, the Speed Limit Point isn't enforced and you can maintain high speed until FL100. Also in reality it tends to be vectors from before MARGO, eventually vectoring to the east of the city of Edinburgh for a RW24 arrival, or south west of the city near the towns of Bathgate and Livingston for a RW06 arrival.
Regarding the TNT restriction, you can use the methods described or for a rough guide use your Mach no. as miles per minute, i.e. at Mach .70 you're doing roughly 7 miles per minute
Example.
FL350 cleared FL280 20nm before TNT
If you were 50nm from TNT, and needed to be level at FL280 20nm before TNT, you have 30nm to lose 7000', at 7 miles per minute (M.70) you have 3 minutes roughly (7x3=28) so the descent rate required would be in the region of 2300fpm. This is ballpark stuff and might need adjusting regarding strong head or tailwind but should see you there or there abouts. If you haven't got fancy Nav kit this method works well.
If you do have a sophisticated FMS, with a lower level selected on the MCP, and being in a descent mode (LVL change or VS) it should paint a green semi-circular line on the ND, which tells you the aircraft will be level at that point at the current vertical speed, this line takes into account current headwind/tailwind and airspeed and is very accurate, if you program in this distance constraint as bucket_and_spade suggests i.e. TNT/-20, then alter your vertical speed to match the green line onto this new waypoint, you will level exactly at the level selected on the MCP at the point your 'aiming' for.
Be careful regarding this though, not sure how MSFS works regarding its ATC system, but in reality you can be cleared to a higher level and told to 'expect' a lower level by XYZ
Example
"Callsign 123, Descend FL300, expect FL260 20 before Trent"
Now having selected 30000 on the MCP, the descent profile green line will only work out a descent to FL300, so my ballpark method shown above can give a rough guide on what kind of descent rate will be required to maintain the profile until you are cleared further descent when you can then fine tune if you need to.
Sorry for the long post!!! I haven't really discussed VNAV since we don't use it and I'm not overly familiar with its operation.
Atreyu
