Descent question

[TH99999]

I have been watching a bunch of videos and have a question . My vnav doesn’t always descent the way it should. Some videos people descent in V/S and others use FLC. I don’t know the advantages to pick one in the descent ? Also I hear people talking about putting a 30 and 60 miles ring  on the display and don’t really understand why . Is there a video that could be recommended for explaining the rings . 
thanks 

[intj mastermind]

What do you mean VNAV isn’t descending the way it should? VNAV works fine for me, even on STARs with many step down points.

Can you give us an example with the arrival you picked and what the wrong behavior was?

Did you check the altitudes on the FMS LEGs page? If the FMS procedure has incorrect altitudes, they need to be fixed manually. A lot of approaches default to “At or Above” altitude restrictions. Technically correct, but I find that it works better to reprogram them to “At” altitude restrictions instead.

The 30 mile ring was introduced as a rule of thumb in the IXEG tutorials. Most of the time you want to be around 10,000 ft and 250 kts when you’re 30 miles from the airport.

If I’m in mountainous terrain, I draw a 25 nm circle around the waypoint that defines the MSA. Helps with situational awareness and terrain clearance.

[FuelFromButter]

1 nautical miles = 6,076ft

3 degrees = tan(3) = 0.0524

1 nautical miles x 3 degrees = 6,076ft x 0.0524 = 318ft

10 nautical miles = 3,180ft

20 nautical miles = 6,360ft

30 nautical miles = 9,540ft

60 nautical miles = 19,103ft