Following an attempted bombing on Christmas Day, flights into the USA are typically running late due to enhanced security and baggage restrictions.
Additional security staff have been brought in to cover all flights arriving in the States and many airlines are now limiting hand luggage to one item, although they will allow additional bags to be checked into the hold free of charge to make up for this.
It is also likely that passengers will not be allowed access to overhead lockers or the toilets for the last hour of their flights as an additional security measure.