Moving into enemy territory

[Darkman]

What happens if only planes exist in this territory?

Do they have to retreat instantly? (1 space or range)?
Do they stay and able to move in the air movement phase?
Are they returned and not able to particpate in combats this turn? (1 space?)

Rulebook states only that if units move into a territory where enemy returned planes are , then these planes are retreated again and fly their range to friendly territory.
This incooperates a bit because retreated and returned planes can only fly 1 space in previous phase and then fly their range in mechanized phase.
Wonder if they can also fly their range again in landing phase? (after mechanized phase)

[Mark]

OK - I think I understand the question - below is my take on it:

If planes are "in the air" - for example they were retreated from a battle after the combat phase - but not 'landed' and enemy units enter their space - they are just moved again one space back and remain 'in the air'.

If planes are not in the air - they have not moved yet and are still on the ground - and enemy units move into their space (and there is no battle - the planes are the only things in the space), then they have to retreat their range and may not fly for the remainder of the turn.  They get displaced and are out of action for the turn as their airfields were overrun. 

Leaving at least one ground unit in the space with your planes prevents this from happening.  As long as there is a battle, the planes do not have to flee the territory and may fly normally on the movement or mechanized phase.

hope this clarifies.