i have a question sir, when you have drawn the graphic of two ac flying closest to each other but with two different QNH, how can it be possible if the local QNH is equal for all aerodromes in that area? maybe a difference can be done if we talk about the QNE and QNH that once you passed the TA you will set on your sub scale the standard pressure 1013.25hpa...
You are not necessarily flying to an airport within the same are with the same local QNH which is why it is very possible to be flying around on different QNH settings. That diagram is telling you why it is important that we do change to standard and fly using flight levels
Do you mean the example at 11:30? If so then no, pressure reduces with altitude so 1013 will be above the 1031 so our new starting point is higher up and we have a shorter distance between it and our aircraft.
