Pressure ALT

[JohnGV]

Hi Gemma!

Thanks, very helpful, i only wish i had that sooner yesterday lol!

yes, i did realise this after my girlfriend pointed it out to me. i was forgettin the basic principles of maths! haha

The two formulas are not the same actually, which is where i was going wrong!

in the first, i had no brackets [like this] only ones (like this) i was forgetting that i had to multiply standard pressure with 1000 and then multiply current altimeter setting by 1000, then do the subtraction and then add on the 2000 feet ground eevation! problem solved now.

Then i moved onto density altitudes, found it even more impossible but then realised (TAKE NOTE ANYONE READING FOR DENSITY)

BEFORE you can do the formula for density altitudes, you must first remeber that

1) with every thousand foot of pressure altitude, standard temperature decreases by 2 degrees

2) with every 1 degree of decrease from standard temperature, you must add 100ft (or subtract 100ft if actual temp is below standard temp) to your pressure altitude.

Armed with this you can then proceed to calculating your density altitude;

pressure altitude + [100 x ( outside temp - standard temp)]

so heres an example

Example - 1,500ft + [100 x (20 degrees - 15 degrees)]

so first do your deductions to temp and inrease in altitude (dont do what i did and ignore them lol) then you get this;

1,800 + [100 x (20 degrees - 12degrees)] = 2600ft

you have a density altitude of 2600ft

Hope that helps people like me understand it!!

Johngv