Cheers mate I failed my first ppl because I forgot how to do weights and balances and weather got 65% the seconded time I got 68% I new it but silly mistakes ... I will sit it again in 2 weeks agrrrr I've done all your ppl cyber exams 68%72%90%65%68% ...
Man so stressful one day I'm happy the next day I feel like I don't know it ...up down up down....I've noticed on a few of your cyber exams for example you will have a distance from one place to another on WAC I've measured it and the minimum is 92nm and yet yours will have 87nm I can't remember the Questions but some are way out with your WAC distance from one town to another...anyway I am praying I'll pass the next PPL CASA exam.
The -12° is what the ISA temp should be at 13,530' based on the standard lapes rate of 2° per 1000'. So the difference between ISA MSL temp +15° to the ISA temp of -12° at 13,530' is 27°.
The deviation in this question is found by subtracting the ISA temp -12° from the actual, or, ambient temp of 22°. This gives you the answer of 34° deviation.
The pressure height is 13530 ft. The expected temperature in ISA at 13530 ft is closest to -12 degrees Celsius (15 - [2 x thousands of feet] = 15 - [2 x 13.5] = 15 - 27 = -12). We have 22 degrees OAT so that means we are 34 degrees warmer than the ISA temperature. Think of a thermometer. Count how many notches there are between -12 and 22 degrees Celsius on the scale.
Each degree of warming has the same "thinning" effect on air density as going up 120 ft in altitude so the temperature reduces the density by [34 x 120] ft or, 4080 ft.
We now adjust the pressure height by 4080 ft to get the final density height of 13530 + 4080 = 17610 ft. That means even though the aircraft is flying at 13800ft, it will actually perform as if it is in air at 17610 ft.
I used to think of a Beer glass when applying the deviation in density height calculations.
The cold,dense parcel of air at the bottom and the same parcel of air at the top just hotter and thinner and gives us the beer glass shape.
Like all good beer glasses the Australian Hotels Association logo (AHA) is on the side.
AHA stands for: A - Air H -Hotter A - Add
Air hotter than what it should be, I add the deviation.