Originally Posted by
Furry
But how it's possible to issue tickets into other airlines stock with A3 flight numbers if the itinerary only includes A3 flights? Ok, might be possible to issue OA 390-stock as they are "same" company, but not for others. With connections on UA for example it's possible, but don't think only with A3 flights.
Any airline that has a relationship with Aegean can issue tickets with Aegean segments on their ticket stock. One such example is United, you can book tickets on their website containing only Aegean segments. Such ticket would be issued by United.
OTA's can use this fact to compare prices, for the same flights, through different airlines. Normally going direct with Aegean would be the cheapest, but in some cases it may be that eg United is actually cheaper.
Therefore you are not guaranteed that a ticket with only Aegean segments is always issued by Aegean. Through OA is indeed a common case (which also means that the tickets cannot be upgraded with a coupon by the way), but others are also possible.