hi
what you're trying to do looks like near the impossible to me.
even to get the plane to just go to the other airport and land is hard enough. AI is scheisse when it comes to aircrafts.
Anyways, your best chance would be to make a looping script for this using gamelogics to get coordinates of the planes route and NOT waypoints.
so basicly the script would look something like this
execute with [] exec "flyroute.sqs"
_wp1 = getpos gl1
_wp2 = getpos gl2
_wp3 = getpos gl3
#1st
_height = 0
plane1 domove getpos gl2
@?(distance plane1 gl2) < 100
plane1 domove getpos gl3
@?(distance plane1 gl3) < 300
plane1 land "land"
#land1
_height = getpos plane1 select 2
?_height < 1: goto "wait1"
~0.5
goto "land1"
#wait1
~60
#2nd
plane1 domove getpos gl2
@?(distance plane1 gl2) < 100
plane1 domove getpos gl1
@?(distance plane1 gl1) < 300
plane1 land "land"
#land2
_height = getpos plane1 select 2
?_height < 1: goto "wait2"
~0.5
goto "land2"
#wait2
~60
goto "1st"
something like that. fiddle with the values and stuff