Hi guys,
The benefits of travelling extra crew with spanish airline is quite controversial.
The two main problems are that most of foreign airline don't do the same so it is quite unfair as there is no reciprocity and people are afraid that if they spread the word on how to do it, then there will be too many people taking benefit of it thus the privilege may end.
But what they do in heathrow is that the ground personel ask by radio the captain on behalf of the guy wanting to travel as extra crew, after having showed licence, passport and company card.
If the captain agrees, then they issue a written boarding pass to go thru security.
Every single airline crews should fight with their company, so all of us pilot can benefit from it.
Cheers