Airline delay claims are typical small claims in that whilst highly complex issues arise of both fact and law, they are generally of a low value. Costs can be recovered but these are fixed costs. Where a flight has been cancelled or delayed in excess of three hours, there is a right to compensation, so long as the cause of the delay was not for exceptional circumstances, such as a volcano eruption, and that the airline took reasonable steps to avoid the cancellation.
EC Regulation 261/2004 (the “Flight Regulation”) creates a statutory framework for compensating passengers on regulated flights to compensation if the flight is cancelled or delayed for 3 hours or more.
Claims are relatively simple once you have established you were delayed on a flight, then it is for the airline to prove that you should not have compensation. In the majority of cases there should be no requirement to litigate at all.
There can be some complications were the delay is as a result of air traffic control direction or political instability in the contrary of origin. The case of Blanche v EasyJet  EWCA Civ 69 gives some indication of how a defence maybe run, which is below.
If you have been delayed by more than three hours please look at my pages on how to make a claim, which is here