What is the problem with the altimeter and cross country flying
An aircraft flying towards a low pressure system will be steadily decreasing as the pressure is going down but the altimeter qnh hasn’t been changed.
A good example
an aircraft is flying at 2000ft with altimeter set to qnh 1012
Then flys into low pressure system 1006 without changing the qnh.
For every 1 hpa is 30 foot
this means over his course from point a to b
6x30= 180ft
meaning he is flying at 1820ft.
Flying change of pressure (good trick)
Flying from high to low? look out below.
Flying from low to hgih? watch the sky.
Flying towards a change in temp
A similar problem occurs when we fly towards an area with a different temperature
As the air gets colder it gets denser and more heavy meaning it will descend even with a constant qnh
same with air that is going from colder to warmer you will climb with the qnh set.
