Altimeter settings with the SquawkBox-POTW system

Preliminaries

In order to use this functionality, you must:
- install the SquawkBox - POTW system and know how to use it (to have read and understood the manual).
Reminder, the SquawkBox - POTW page is available here.

- have an elementary knowledge about altimeter setting, QNH and QFE, and standard atmosphere.
Otherwise, you have to refer to these lessons here.

Principle

One of the big advantages of the POTW system is to be able, at any time, to fly all around the world with a real weather report.
And all that, whatever the method: in group for a network flight or alone for a solo flight. You have to start the POTW system, to tick the "Auto Weather" box, and you'll receive automatically the METAR bulletin for the closest airport.

So we have the opportunity to be able to proceed to the altimeter settings "as in the real life". What a bit of luck!

However it's necessary to by-pass some Fly!'s bugs, as the return at 29.92 during every new METAR loading, or some difficulties in managing the metric system (hPa), abandoned for the benefit of inches of mercury (inHg).
The POTW "crazy testers" team (Gilles and Fred notably) led Roland to finalize this trick, apparently complex but not difficult to use.

Let us see that in images (click every image - except the bottom one - to enlarge it).

I start the "POTW system". I have ticked the "Auto Weather" box (automatic weather report), so I receive the METAR for Clermont-Ferrand (LFLC).
The interesting value is the pressure: A3014, which means 30.14 inHg (after conversion into hPa, I'll have the code Q, that is to say about Q1020).
I record this data wit care. It's the regional QNH (pressure-altitude-sea, for the Clermont-Ferrand area, that day, at that precise moment).

On my altimeter, the altitude is right but the pressure is false (the standard 29.92!).

Let us apply our method for correction: in the Fly! menu, I select "Weather / Other".

Those who would be surprised that the menu is in English are eliminated: it's mandatory for network flight ;-)

After some seconds, my barometer moved. The pressure is always 29.92 and I have to set the exact value.

Naturally, the altimeter is false until I do the correction.

Let us come back to QFE (pressure-altitude at ground level).
This page allows you to do an approximate calculation. Follow this link and read the explanations.
Here's the result!

That's all, it's dead easy, eh?
And then? Well, we can start and make the foreseen flight, after all it's the objective :-)
Two solutions occurs to us:
1 - It's a local flight. In this case, I let the "Auto Weather" box ticked.

2 - I make a rather long flight so that the weathear risks to change. In that case, when I reach my flight level (either as soon as I reach the transitional altitude), I can tick the "Auto Weather" box again.
For the record, if I use a VFR or IFR flight level (FL 55 for example), I have to set my altimeter to the standard pressure 29.92. It's vital for safety..

Then, in the arrival, it's the same operation: it's absolutely necessary to avoid METAR loading during the final approach. So we have to load the weather report at least 10 minutes before the arrival, make the QNH and QFE modifications, and stop "Auto Weather". We shall have taken precaution to take out in advance the index card for the destination airport for checking its altitude, naturally.

The interest of the QFE setting (which is not used in all countries) is to give a "zero" value to the destination airport altitude. It avoids calculations at the moments when we have other things to do: to maintain the speed and descent rate for example ;-)
Naturally, a pencil and a paper are useful instruments, because the mental calculation may be false in an unusual situation, and we aren't entitled to error for managing the altitude.

These settings (is it necessary to point it?) are used in every "journey" flight in the real life, and they've obviously an essential importance for safety. Control tower or AFIS communicate the values for QNH and QFE. IVAO or Vatsim controllers also do it.

Have nice flights with POTW !