Background to question 2.
Two hours earlier from the scenario in question 1, you took off from a Class D aerodrome with ATIS. Before take off, you did a pre-flight altimeter check in accordance with ENR 1.7. For simplicity, assume that both altimeters in your aircraft were exactly 50’ ‘off’ in the same direction. (For present purposes, I’m not going to reveal ‘which way’.) In accordance with ENR 1.7, that error is acceptable (for both VFR and IFR flight) and you take off.
Fast forward two hours and 150 nms, when the circumstances and assumptions as are set out for question 1 apply. But you now know that that the altimeters in the aircraft have a 50’ error.
Question: What is your altimeter’s actual height above the sea below?
(a) 500’.
(b) It could be anywhere between about 400’ and 700’ (if the altimeter error is a 50’ under-read) or between about 300’ and 600’ (if the altimeter error is a 50’ over-read).
(c) It could be anywhere between about 475’ and 625’ (if the altimeter error is a 50’ under-read) or between about 375’ and 525’ (if the altimeter error is a 50’ over-read).
(d) None of the above. The correct answer is [specify].