Pre-Flight - TO/FROM Computes from PPOS?

Hi,

Not a big deal, but I noticed that when sat on the ground and the IRS is not ON or aligned, that any airport pair I enter in the FMS computes (in some cases?) from PPOS and not based on the position of the FROM airport entered.

e.g.

Sat at Heathrow, entering EGLL/SCEL shows a distance of somewhere around 6500 nm. If I pick an airport further north as the FROM, it is computed as the same distance, even though the airport is some 500 miles further north!

I thought it was interesting.

Best regards,

Robin.