What does to mean in a newspaper headline, for example:
Airline XY to cut cost of pilots' wages
Is it a shorter form of "Is going to" or "Is planning to"?
Yes. Normally it can be interpreted as "is going to" or "has decided to". In headlines, that construction usually indicates that something will happen; a decision has been made.
There is a construction "Airline XY is to cut costs" which means the same thing. All the headline subeditor has done is to remove the verb "is" (as they often do).