Deadlines
Many negotiating skills courses advise that deadlines are best ignored. To acknowledge them is to give your opponent a potential lever. Why would we want to do that? So stop worrying about 31st May. Instead, how about imposing one of our own for them to try to ignore? Pick something from our must-have list that is simple to implement (say by just spending some money) and set our own deadline. Present it as a token of goodwill that they truly are negotiating in good faith (pause for laughter). But when? How about 9th July - the fifteenth anniversary of a day that will live in infamy in the history of our airline. If they do ignore it, then that will confirm for certain what we probably all already believe in our hearts. The leopard has not changed its spots; not even by the slightest fleck.