Originally Posted by
kraggy
hi folks,
the question below is one i came across when googling for a diagram that explains qnh and it's wrecking my head!
could anyone explain the answer in simple terms as i've totally blocked out on it.
thanks in advance.
k
"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 ?
Hey Kraggy and other altimetry buffs,
Spare a thought for some of your military brethren. At Newquay Cornwall Airport/RAF St Mawgan we are authorised to control in the Director's pattern, vis cct and departures with mixed ac ops on QFE and QNH. It works out quite simply provided you get your head around the coordination problems early. Some of the ATCOs stick to Flight Levels whenever possible! Seriously, it does work very well and the separation (No RVS on QNH ac) and obstacle clearance (No ROC on QNH ac) rules do subtly differ. The whole thing arose because of electric jets being unable to set QFE on their primary altimeter - leap in technology eh!? Guess who got the original (30 page!) Safety Management task?