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To begin with, 120kts is 2 miles per minute. That's great for rough figuring. Dig out the old whiz wheel. Find 12 on the outter scale for 120kts and place the index under it. Move around the outter scale to 21 for 2.1nm & read the time under 21. 1 minute & 1/2 of 1 second.
Although it is really splitting hairs, when the distance is less than 10 miles or so it is generally better to use the "seconds" index. This is at the "36" mark on the inner ring. Place "seconds" under 12 (for 120 GS) on the outer ring. Find 21 on the outer ring for 2.1 miles, read down, 1 minute and 3 seconds.
don't pull the whiz wheel out inside the FAF or the IAF or even after you start your descent...120 = 2nm/min...you have roughly 2 nm so its 1 min or 60 sec. Besides that, more times than not it will be calculated for you on the approach plate. Only a few types of approaches don't have the time calculated for you and sence you can't do those types of approaches based on time you can estimate your time and call it good. Don't be found in a burning wreck with a whiz wheel in your hand.
It's just an exercise in knowing how to use the go 'ole E6B. For those of us born before the calculator, CD's and the like it is a round slide rule and a lost art. It can perform a lot of functions. Of course nobody in thier right mind pulls out the wiz wheel FAF inbound.
Do you know how to do a weight shift problem with the E6B??
Don't have to....can do that in my head Besides, that wasn't my point, I believe in using the E6B, just not in the situation that was mentioned. Has everyone forgot the time honored method of "in your head" calculation?
It's just a proportion, as you learned in high school.
Here's a cool one you can use to calculate rate of descent on a standard three-degree glideslope.
First, you have to know your groundspeed. Let's say you use a 90-knot IAS as your standard approach speed. Then, you have a 10-knot headwind component. So what rate of descent do you set up to hold the glideslope?
Place 3 over the 60 pointer on your whizwheel. Your groundspeed will be 80 knots (90 kts IAS - 10 kts headwind). Look for 80 on the bottom scale and look up. You'll see 40, which represents the 400 fpm descent you need to commence when the glideslope needle centers.
That one courtesy of my Alitalia students and their training captain at FSI.
I've been reading most everything in here and I have to admit I'm having a whole lot of fun with this thread in particular. There's been an number of poignant axioms about continuing education. Perhaps I should change my name to Sponge. These tips & tricks are outstanding!