gnvav8r
Member
- Joined
- Apr 8, 2007
- Posts
- 20
Computer Navigation Fixes (CNF) show up on some GPS plates... often on a DME arc, so that the GPS can give you guidance on when to start a turn. They are also used by the GPS on approaches that lack a FAF (such as a VOR overlay approach). The GPS can do the RAIM check and in the case of WAAS units do the HAL and VAL (Horizontal and Vertical Alarm Limit) check before switching to the final approach mode. So much I've read...
I understand that it is important to go outbound far enough on such an overlay approach to put the CNF behind you, so that after the procedure turn is made it will be in front of you allowing the GPS to do whatever it has to do before switching to the final approach mode. (Well that, at least, was the subject of a Flying Magazine article in Dec 2006 in with Richard Collins did not fly outbound far enough on the ILS at Asheville, NC)
Yesterday I flew an Angel Mission into Craig Field (KCRG), and though it was VFR I did study the approach plates. The VOR/DME or GPS to 32 caught my eye... and raised this question, which I hope somebody can clarify for me....
It has two CNF's on it. CETER is the MAP and that is clear enough. It showed on my GNS430.
But the other one CFLFF does not show on the approach procedure as it loads into my GNS430. AND it is 6 miles out from BEABE. How do you know when you have flown out far enough to do the procedure turn, when it does not show on the GNS430? And being so far out, that leaves relatively little room to do the procedure turn and still stay within 10 nm.
My question therefore is... maybe I have misunderstood the nature of CNF's and the need to fly outbound beyond them?
Any advice?
Pete
I understand that it is important to go outbound far enough on such an overlay approach to put the CNF behind you, so that after the procedure turn is made it will be in front of you allowing the GPS to do whatever it has to do before switching to the final approach mode. (Well that, at least, was the subject of a Flying Magazine article in Dec 2006 in with Richard Collins did not fly outbound far enough on the ILS at Asheville, NC)
Yesterday I flew an Angel Mission into Craig Field (KCRG), and though it was VFR I did study the approach plates. The VOR/DME or GPS to 32 caught my eye... and raised this question, which I hope somebody can clarify for me....
It has two CNF's on it. CETER is the MAP and that is clear enough. It showed on my GNS430.
But the other one CFLFF does not show on the approach procedure as it loads into my GNS430. AND it is 6 miles out from BEABE. How do you know when you have flown out far enough to do the procedure turn, when it does not show on the GNS430? And being so far out, that leaves relatively little room to do the procedure turn and still stay within 10 nm.
My question therefore is... maybe I have misunderstood the nature of CNF's and the need to fly outbound beyond them?
Any advice?
Pete
