Hi all.
In light of the recent conversation about the quadrantal rule (see
http://www.pprune.org/forums/showthread.php?t=217051), I was hoping for a bit of explanation on the finer points of the semi-circular rule.
I'm currently preparing for my final NATS interview and this is in the material but I'm not sure I understand it completely. Essentially the book given to me by NATS to study says the following:
Inside controlled airspace when flying IFR above FL245, the following applies:
Heading 000 - 179 - FL250 is the lowest usable FL, then increments of 4000ft from FL290 @ odd FL's.
Heading 180 - 359 - FL 260 is the lowest usable FL, then increments of 4000ft from FL310 @ even FL's.
It's the second part that gets me; I understand that 4000ft from FL250 is FL290 and then so on. What I dont get is a) why the massive seperation distance of 4000ft when surely 2000ft would suffice to allow minimum seperation while leaving room for opposite direction traffic and b) why do the westboud flights have to jump from FL260 to FL 310 (5000ft when everything else is 4000ft)?
Now I'm suspecting that the reference in my book from NATS about the next westbound FL being FL310 could just be a typo, but I'd like some clarification on this if at all possible.
Many thanks in advance,
B