[QUOTE
"A plane leaves an aerodrome "A" which is 500' above sea level with a qnh of 990 mb and flies to another aerodrome "B" which is 200 ft above sea level with a QNH Of 1010. Assuming the pilot doesnt recalibrate altimeter from QNH at aerodrome "A" and maintains a height of 500 feet after leaving aerodrome "A" what is his actual height above runway level of airport B ? Whats his height above mean sea lever ?[/QUOTE]
Poorly worded question but here is my take on it. He leaves airport A and climbs to an indicated 500 feet, the datum on his altimeter set to 990mb QNH. As he flies towards an area of higher pressure, he effectively descends although his alt will still be reading an indicated 500 feet. The difference between the two QNHs is 11mb; about 330 feet. Therefore his vertical distance from sea level has reduced by that much. So if he is flying along with an indicated 500 feet on his alt, given airport B is 200 feet above sea level, he would be 30 feet underground by the time he gets there as he would only be 170 feet above sea level.
The question maybe implies that he is flys out of airport A at 500' above ground level; but to know that he would have set QFE on departure.....
Makes perfect sense after a bottle of red.