A few that spring to mind:
- Fuel costs over $90 per barrel
- Media making aviation out to be the world's main problem with regards emmisions
- Government pouncing on the latter notion by enforcing taxes on flying in order to increase tax revenue
- New initiatives like the St Pancras train station and new high speed line, which no doubt eats into demand for flights
Can't think of any other for now, hope they're of use.