Question regarding VOR intercepts inbnd/outbnd

[Bizjetdriver142]

hi everyone,

been pondering this for a while:
Is there any working rule of thumb for the intercept from inbnd to outbound radials which prevents overshooting, in other words, how many miles prior to the VOR to start the turn for a smooth intercept without over- or undershooting the desired outbnd radial?
For example, you 're tracking inbound on the 090 radial and have to leave the VOR
via the Radial 180 ( be it as a chart procedure or because ATC advises you to).
So its a 90 degree course change.
With small slow plane no prob, but a fast bigger Jet will overshoot the VOR if you start the turn too late.
In my plane the FMC does its magic and always gets its perfect,it calculates the manouver so that the turn starts prior to passing the VOR and the plane rolls out exactly on the selected outbound radial.

So is there any rule of thumb to calculate this kind of distance of lead when flying raw data?which also works for inbound to outbound courses other change than 90 degrees?

I faintly seem to recall something like GS/100 = NM prior to station for a 90degree difference between inbnd and outbnd, but that doesn#t work out so well in reality.

As an offspring to the main question: Does anyone know by chance what the JAR/PANS OPS regulations say to the above scenario?is it required to fly the manouver like the fmc calculates or to overfly the station and then do a re-intercept of the outbound radial?

Thanks in advance for your help,

Best regards,

John

[Intruder]

Try turn radius ~ 1% of TAS. At 300 kts, turn 3 NM prior.

[Microburst2002]

I calculated my own rule for that using radius of turn formula:

If you know your NM per minute, square it and divide by 10, you have the anticipation for a 90º turn at about 25-30º bank angle.
You can divide or multiply the result if you have more or less bank or the turn is more or less degrees.

thinking in NM per minute is useful for several things and is very easy in modern airplabes where you have TAS and GS displayed. You don't have to bee too accurate. With time is like knowing a table by heart:

120 kt-----2 nmpm
150 kt-----2.5 nmpm
180 kt-----3 nmpm
210 kt-----3.5 nmpm
..... --- .......
420 kt-----7 nmpm
450 kt-----7.5 nmpm
480 kt-----8 nmpm
510 kt-----8.5 nmpm
540 kt-----9 nmpm

and son on.

for instance if you are flying during climb out and are instructed to leave a waypoint with a 50º change, with TAS 350 kt you can make it with 25-30º bank angle, so you need aproximately 6^2/10, about 3,6 miles for a 90º change, so about half that for a 50º change, plus a little bit to allow for time to bank into and out of the turn. Say about 2 miles.

If you are flying en-route at high altitude, bank angles should be less, say 15º. So for a 90º change of heading at 557 Kt you will need 9^2/10*2, about16 miles plus bank time allowance, say 17-18 miles.

I tried it in the sim (yes, the MS FS) and it worked really well so I gave the rule as good. Sometimes I use it in real life airline flying and I am proud to say that it works very well, too. I use it for DME arc anticipation, too, although there are very few occasiones where I can hand fly a DME arc approach.

I have noticed that my rule gives different results than the 1% rule, specially at high speeds. I think my rule is more accurate.