Pressure Alt Conversion
 

Can anybody please remind how to figure out the pressure altitude conversion. And also, the "how many miles traveled along a DME Arc" formula. Thanks.

Wanna just tells us which interview you're studying for and put all the questions into one post? It might make for quicker responses :)

Also...can you be a little more specific on what you mean by "pressure altitude conversion". That could reference several different things.

current alt setting minus 29.92 multiply by 10. Then take that number and add/subtract to the field elevation.

the dme one, idk if there is an easier formula but using geometry I came up with a formula.

2*pie*dme*degrees traveled all divided by 360.

ie, if you started at the 180 degree radial and ended on the 270 degree radial that would be 90 degrees traveled

so 2*pie*dme*90 all divided by 360

Figure out the difference between 2992 and current altimeter setting. Drop the decimal point and add a zero to the end. Then add or subtract the figure to field elevation. Example (30.22 (current setting) - 29.92 = .30) drop decimal point to eqaul 30, then add zero to the end which equals, 300. Since pressure is higher than normal subtract the 300 from the field elevation to give you your pressure altitude. So if your field elevation was 1200 ft, you pressure altitude would be 900 (1200-300=900 ft) The current pressure therefore simulates that you are at 900 even though the actual elevation is 1200. Hope this makes sense.

yea neglected to say drop the decimal

We know that at 60 miles, each degree is 1 mile apart (roughly). So at 60 miles, the entire arc is 360deg and 360 miles. IF we divide the arc into six segments, each segment is 60 miles.. the same distance as our position from the station. So... each 60deg arc is equal to the distance to the station. Each 30deg arch is half the distance.

FWIW, arcs are never less than 7 miles and never more than 30 miles.

If you arc around from the 270 radial and then intercept the 300 inbound, you have arced 30 degrees which will equal half the distance from the station. 10 miles from the station? 5 miles... on the arc.

google 'DME arc' and you can find lots of articles on arcing and how to fly arcs. Also how to figure lead points to intercept the arc and to intercept the inbound course.

Go to http://tinyurl.com/ycvtk7. What is the distance (roughly) from Barbs to the intercept? (271 around to the 219...)

It is Standard Alt. setting(29.92) - Current alt. setting. This avoids the mixup of adding or subtracting to field elevation.
And i multiplay answer by 1000. But thats not important.

Example: 29.92-30.22= -0.30
-0.30*1000= -300
-300+Filed elevation(1200)
=Pressure Alt. 900 ft.

Do you fly out of Daytona?

I used to instruct there.

For the DME arc rule, just remember the 1:60 rule (1 degree of arc at 60nm equals a ground distance of 1nm). The ratio is easy to scale down: 1 degree of arc at 30nm equals a ground distance of 1/2nm, 1 degree at 15nm equals a ground distance of 1/4nm, etc etc.

Eaxmple: Arc 70 degrees at 13DME
A 13nm arc is pretty close to 15. If I am arcing 70 degrees, just divide 70 by 4 (because at 15DME each degree is 1/4nm) and you get about 18 nm. No need to get fancy with calculators and what not. I had that exact question sprung on me at an interview. I think if I had asked for a pen and paper or a calculator I would have been laughed out of the room.

II Corps got it right 60 to 1 is the ticket

here's a litte extra

60NM from the VOR 1NM = 1 degree
6NM from the VOR 1NM = 10 degrees

from there you can always extrapolate:
30NM from the VOR 1NM = 2 degree
20NM from the VOR 1NM = 3 degree
15NM from the VOR 1NM = 4 degree
12NM from the VOR 1NM = 5 degree
10NM from the VOR 1NM = 6 degree

if you wanna be exact:
60 divided by DME = degrees per NM

As always, the AFMAN 11-217 Volume 2 is a great source (Chapter 6):
http://www.e-publishing.af.mil/pubfi...an11-217v2.pdf


Cheers
George