View Full Version : Lead Radil To Intercept From Arc To Radial
Hey There .. I Want Know Exactly The Formula Or The Way To Get The Lead Radial To Intercept From Arc To Radial .. And I Know Some Approaches Plate It`s Available There Special On Ils Dme Approach Plate .. But Should I Calculate It Also For Vor Approach Or Not ?
Thanks In Advance.
Prat At The Back
8th Dec 2009, 12:40
I've always used the 1 in 60 rule.
For instance the arc to ILS at Inverness rwy 05 is a 13 mile arc and the lead radial is 10 degrees prior to the inbound.
On a 12 miles arc each degree is 12/60 miles = 1/5 th of a mile. Thats near enough 13 miles for me to make the sums easy.
10 degrees would equate to 10 x 1/5, approx 2 miles before the radial required.
2 miles before the radial seems a good cut, if you left it any later you could risk going through radial
rsaf1
10th Dec 2009, 02:12
ok i got it .. .but i`m wondring should i make lead radialalso for vor approach or that just for ils approach ?
despegue
10th Dec 2009, 08:56
Sorry but I might not understand your question correctly, however, a good mental calculation on when to start to intercept a DME-arc or radial is:
0,5% of the current Ground-Speed = Distance needed to complete the turn.
example: Ground speed 240kts
D= 1.2 NM to the arc start to turn.
deeceethree
10th Dec 2009, 09:37
rsaf1,
I realise that english is probably not your first language (but good effort, well done!) so I will try to keep this simple.
An ILS does not have any radials like a VOR. However, I think you are asking if the principle of turning from an arc approach onto an ILS localiser is the same as turning from an arc approach onto an inbound VOR radial? The answer would be yes.
However, unless you have an airfield where a VOR is situated close to the ILS, to give you lead radials for your turn on to the ILS, then you need to devise some other method to warn you to begin the turn. I believe that is what the other posters are doing for you on this thread. When using such methods you may also need to account for the wind, particularly if it is very strong. For example, if a strong wind is coming from behind you, as you turn you turn on to the localiser or VOR radial, you may be pushed past the localiser/radial.
None of the methods is perfect, and it depends on the speed of your aircraft, and if any strong winds are affecting the turn. Only time (practise and experience) will let you know what works for you.