Originally Posted by
gregsfortytwo
Joint Ventures are not the same as alliances. Delta and AF/KLM, and Delta and Virgin Atlantic, (and soon, Virgin Atlantic and AF/KLM!) have Joint Ventures on transatlantic flights. I don’t know the exact details (not sure it’s public) but they do some degree of joint planning and pooling money over routes they fly from the USA to Europe (and back). That’s why you’ll see some routes where Delta pulls out and Virgin takes over all their slots, or airports where all the groundside operations for one of those airlines are handled by employees of the other.
My understanding is that flights covered by the at least the AF/KLM JV (that AFAIK had its origins in the early PMNW/KLM JV that started the trend) are supposed to be revenue neutral so that neither airline cares which flight you take or how it's booked. OTOH, one frequently sees significant fare differences, so I'm skeptical about how this works in practice.