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PPL Volume Progress Test 2 q11 wrong answer? (Errata?)

HardnLumpy created the topic: PPL Volume Progress Test 2 q11 wrong answer? (Errata?)

Hi

Progress Test 2 q.11 (page 245) asks for a distance to descend to 1500 AGL.
Aerodrome Elevation 1500ft
Cruise A065
Descent 500ft/min
GS 140kt
QNH Same

If QNH are same at departure and arrival then the Aerodrome Elevation at 1500ft = 0ft on the altimeter.
Therefore to arrive at 1500ft AGL is a descent of 5000ft not 3500ft?
The answer diagram shows a subtracting of 1500ft between AMSL and the aerodrome elevation. A total of 3000ft to arrive at 1500AGL
Same QNH setting means this 1500ft altitude calculation is already allowed for. It zeroes out.
My answer is D 21nm to descend 5000ft (which is still 1 mile short, I get 22miles)
The described answer is B 16nm to descend 3500ft

Am I missing some abvious clue between AGL and Elevation, or is this answer wrong? (Why do I suspect the former...lol)

When I am in flight my ToD to arrival calcs are usually within 1min, off the top of my head. So why am I so stuck on this one? Very frustrating....I've missed something....

Stuart Tait replied the topic: PPL Volume Progress Test 2 q11 wrong answer? (Errata?)

Hi Rich
I think you'll find if you set the QNH to the 0 on the ground at the arrival airport it wouldn't match the Area QNH that the question tells you is the local QNH
also the question doesn't say you departed from the same field.

bobtait replied the topic: PPL Volume Progress Test 2 q11 wrong answer? (Errata?)

Just adding to what Stuart said. It seems you are confusing QNH with QFE. If you set the QNH at the aerodrome, the altimeter will not read zero on the ground. It will read 1500ft on the ground at that aerodrome. If the local QNH is the same as the area QNH then both cruising level of 6500 and the elevation of 1500 are measured from sea level. If the the aerodrome is already 1500ft above sea level then an aeroplane at 1500ft above the aerodrome is 3000ft above sea level. That means the descent from 6500ft above sea level to 3000ft above sea level is through 3500ft. See the answer diagram on Page 258.

HardnLumpy replied the topic: PPL Volume Progress Test 2 q11 wrong answer? (Errata?)

Thanks guys, I'm with you now.
And yes, my explanation wa's completely wrong , I meant 1500ft = 0AGL not the alt reads 0.
Plainly I got myself in a complete tailspin on this one. Maybe a lesson for me not to fly at 7am with a fuzzy head?!
When I reviewed the diagram with a level head it made perfect sense immediately.