Remedial Help Needed

[MrBrz]

I was looking through the book "Preparing for your CX Interview" and found a question that I cannot answer. If someone would be so kind to help me out I'd appreciate.
It asks: "Given an indicated altitude of 10,000', and an actual OAT of -20C, you set your altimeter to a local station setting of 29.62". If the station is 2,500' what is your actual altitude?"
For all of you who enjoy pointing out peoples mistakes and short comings let me assure you I am well aware of my remedial status. I am reminded how little I know every time I read through this interview material.
Thanks a lot.

[TruBlu351]

This question refers to, "How does TEMP effect your altimeter"? Normally asked WRT LSALT/MEA and OM check heights.

Just remember, "high to low (temp or QNH), in you go". ie: Flying to an area of lower temp or QNH you'll "fly into the ground". ie: your altimeter will over-read, so you'll be lower that indicated....and vice versa.

Here's a few temperature rules of thumb I have (Don't hold me liable!!) and someone dive in if I'm smokin' crack!!.........

For every 5*C below ISA your altimeter will 2% below the actual INDICATED ALTITIDE. (ie: -10*ISA would be 4% and so on).

OR

+4 feet for each -1°C temperature variation from ISA, per 1000' altitude above the airport (MSL I believe).

So at an INDICATED 10,000ft @ -20*C (ISA-15*C as ISA is -5*C) you'd over read by 6% of 10,000ft (3 lots of -5*C) which is 600ft. So your ACTUAL altitude would be approx 9400ft MSL. If the airport elevation is 2500ft, then your are 6900ft AGL.

Or the other way........-15* ISA x 4ft = 60ft. Multiply this by 10 (thousands of feet) and you get 600ft too :8

AND, most importantly, use the force!

[tornadoflyer]

I calculated the question and came up with 9.550 feet.

Just as TruBlu351 mentioned, altimeters will over-/underread by 4 feet per 1 C deviation from ISA above the station reporting the altimeter setting:

ISA at 10.000 feet is - 5 C, so deviation is -15 C

15 x 4 = 60

10.000 - 2.500 = 7.500 feet

60 x 7.5 = 450 feet

10.000 - 450 = 9.550 feet

[TruBlu351]

I calculated the question and came up with 9.550 feet.
Just as TruBlu351 mentioned, altimeters will over-/underread by 4 feet per 1 C deviation from ISA above the station reporting the altimeter setting:
ISA at 10.000 feet is - 5 C, so deviation is -15 C
15 x 4 = 60
10.000 - 2.500 = 7.500 feet
60 x 7.5 = 450 feet
10.000 - 450 = 9.550 feet

I actually just found the answer to the question in my books and it was 9,550! So spot on tornadoflyer!

I was using height AMSL and not AGL in the equation (ie: 10 and not 7.5).

MrBrz, look at Q76 in your XYZ book too. It doesn't fit the ROT, so I'm a little skeptical of some of the answers I see.

ie: On a 3* glide path, OAT -25*C, the OM check HT is 1760ft. What will your altimeter read if on GP?

a)1820
b)1760
c)1720

Well thru the process of elimination it's "a" because it's the only one that's higher (over reading) due to the lower than ISA temp.

My Captain's ABC book says the answer is 2020ft! Gotta love the inconsistencies amongst a few more I've found :mad:

Using the 4ft rule.....ISA @ 1760ft is approx 11*C and OAT of -25*C = ISA -36

Therefore: 36 x 4 x 1.7 = 244ft then + 1760ft = 2005ft (close enough)

Why do these nuts make these simple things harder := :ok: