Ash cloud
 

BBC News - Flight disruptions cost airlines $1.7bn, says IATA

Almost one in three flights around the world have been affected by the closures in Northern Europe.

I never knew European air travel and it's links around the world had so much of an effect on international travel!

However, seeing some of the pictures on the popular airliner photography site, it is clear to see that an aircraft stuck in FRA, LHR, CDG etc. owned by CO, DL etc. may have been needed for Pacific or domestic services over there.

Fascinating stuff!