Green Circles

[coa787]

Hey everyone, I was wondering if you guys could help me out here.

I saw a few photos on here that showed green circles on the Nav Displays (or EHSI's) over fixes such as "5240N" on the NAT Tracks, and they had a little green number next to them for there size in nautical miles, well, I was wondering three things:

1. What determines the size of those circles?

2. When do you use them?

3. Why are they so important?

Thanks!

[B767Driver]

Originally Posted by coa787

Hey everyone, I was wondering if you guys could help me out here.

I saw a few photos on here that showed green circles on the Nav Displays (or EHSI's) over fixes such as "5240N" on the NAT Tracks, and they had a little green number next to them for there size in nautical miles, well, I was wondering three things:

1. What determines the size of those circles?

2. When do you use them?

3. Why are they so important?

Thanks!

Drawing the green circles on the Nav display is a technique many pilots use to remind them of procedural requirements while flying the NAT. They are typically drawn to form a radius +/- 2 degrees of longitude prior to a reporting point.

Pilots perform nav verification procedures prior to flying a new leg on the track, reporting procedures while crossing the fix, and then nav verification procedures after crossing the fix.

In a non radar environment any time estimate in error of 3 minutes must be given to ATC...so they are also used to monitor time over fix as well.

[coa787]

Thanks a lot!