Adding Waypoint restrictions.

[Guest gdafc]

Hi all,How do I go about adding waypoint restrictions? For example;Descenbd FL200 25nm before MID. I know I can use the Place/Bearing/Distance method but it is not easy to work out the necessary bearing for this.Thanks in advance!

[Guest vrandar]

You know which heading you will be flying towards MID so it is fairly straightforward to work out the "reverse" heading and to enter the PBD waypoint. There is no easier way to do it. To make it a bit quicker you can create a small chart in Excel of headings and their reverse headings as a quick reference, or if you send me your email address I will send one to you.

[Guest gdafc]

Ah yeah but!! (Now I am probably Looking at this the wrong way) If for example there are two waypoints between MID and 20 miles before MID then the aircraft will turn twice thus the bearing to MID will change twice and my P/B/D fix will be wrong!!I think it makes sense.Thanks.

[Guest vrandar]

It doesn't matter what waypoints are before MID, your only requirement is to be at FL200 20 miles before MID (if that is the ATC instruction). It is 20 miles on your flight plan, not 20 miles in a particular direction. If you have a change of direction between MID and 20 miles before MID then it makes it slightly more complex but not overly so.Lets take an example of a flight from Glasgow EGPF to Gatwick EGKK. See the first attached photo which shows MID on a bearing of 159 from berek. Suppose ATC gives an instruction to be at FL100 10 miles before MID. The opposite heading of 159 is 339. You can work this out by calculating that 159 is 21 degrees off 180, then taking 21 degrees off the opposite pole of 360 gives 339. Therefore the PBD would be MID/339/20 and you would apply the vertical constraint of FL100 to the new PBD fix from the right LSKs as normal.But if there was a more complex routing that went from BEREK to VAPID then to MID you would find that as VAPID is 19.8 miles from MID you need to be at FL100 0.2 miles before VAPID (19.8 + 0.2 = 20). The bearing TO vapid from barek is 181 so the bearing FROM vapid is 1 degree giving a PBD of VAPID/001/0.2

[Guest gdafc]

I new I was making it difficult and not looking at it practically!! Thanks Rob great explanation I had tried working out all sorts of wierd and wonderful bearings etc..! Thanks again.