You would need to do a query for all the airports, then run through them, and do another query for all the airports except the current one. Then you could output them all like you have above.
Alternatively, you could get all the airports as an array, then use the following code:
$airports=array();
for($i=0;$i<count($airports);$i++) {
for ($j=0;$j<count($airports);$j++) {
if ($i != $j) {
echo $airports[$i] ." to ". $airports[$j];
}
}
}