Not necessarily. The crew could fly HEL-ARN-HEL before the HEL-MAD leg, and the routing for the next day could be MAD-HEL-ARN-HEL. In the past I have flown a similar routing with KLM. The crew spent the night in Helsinki, in the morning they flew HEL-AMS. I was welcomed by the same crew on the next leg AMS-GVA (MXP on another occasion)on a different plane. They told me that they would fly immediately back to Amsterdam and then get the rest. Of course changing to IB-operated flights would save the hotel costs and it would be very nice to see other carriers in Helsinki.

Does Iberia have any crew/planes based in Barcelona (Iberia express) or would the solution be Vueling. Having IB flights would be great for us using BA Executive Club as our FF. Extra avios points, cheaper rewards including free domestic connection in Spain.

If I remember correctly IB and BA have now abandonned overnight stays on the MAD-LHR route. The home carrier flies the first flight from their base and flies the las flight back to its own base.

I am not sure how the partly American (AA or other) crew on the HEL-JFK flights would help reducing the costs . It is not new. Delta used to place one member of crew on Finnair flights when they co-operated. There was an interview of an American crew member in the AY Plus magazine. She was a Finn living in the States. I guess it was mainly done to have some Delta visibility on the code share flights. How about having Russian S7 crew members on the JFK flights or Russians living in the New York area?