Calculation

[boo]

It is 2.1nm from FAF to runway threshold, groundspeed of airplane is 120kts, how long will it take to reach the threshold? Please show me how you got your answer.

 

[Rvrrat]

Time distance calculations

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.

 

[MetroSheriff]

boo,

I'll take a stab at it.

120 kts GS is 2nm per minute, or 1nm every 30 seconds.

2.1 (miles) X .5 (half minute) = 1.05 minutes

1.05 X 60 (seconds) = 63 seconds

 

[chperplt]

To get more anal

120Kts/hr GS = .03333 nm/s

2.1nm/.0333 nm/s = 63.063 seconds

 

[MTOP_set]

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.

 

[MetroSheriff]

Rvrrat,

You are on the right track. Just the wrong scale. that's .05 minutes, not .5 seconds.

.05 (minutes) X 60 (seconds) = 3 seconds.


Chperplt is actually the MOST correct, I just couldn't make out the .0633 on the dial of my E6B altimeter/flight computer watch. LOL!!

 

[ksu_aviator]

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.

 

[MTOP_set]

ksu

relax,

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??

 

[Rvrrat]

Still learning more

Thanks for the heads up on the correct scale!

 

[ksu_aviator]

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?