Another idea: a zone at the farthest size of the map of each country used as an aerial spawn zone.
The zone may be a box of 10000 feet tall between 5000 and 15000 feet, 10 miles long along a map border and 2 miles width. When u spawn there u are placed heading towards your closer surviving base, at a random altitude and position inside the box and at 2/3 of your maximum speed for that altitude, WEP off and max man and rpm.
If your plane can load drop tanks, that loadout will be selected automatically and u will spawn with the drop tank/s empty and the selected internal fuel till 100%.
If the selected plane can't use drop tanks, you will spawn with a maximum of 50% of fuel.
That spawn zone is deactivated untill your country is reduced to three airfields. When your country is reduced to less than 4 bases, the zone is activated and placed automatically in the border of the map closer to the surviving base farther from the centre of the map.
This feature may simulate reinforcements comming from outside the map.
