An airline’s official arrival time has been determined as the time its doors are opened rather than the time it touches down.
A case was brought to European Court of Justice which took the decision.
The ruling will affect compensation claims for flight delays.
Budget carrier Germanwings claimed that a delayed flight had landed with a delay of two hours and 58 minutes, making it just shy of three hours. This, it said, meant that it did not have to pay compensation.
However, it was more than three hours late by the time the doors were opened.
After a delay of three or more hours for a short-haul flight, compensation of €250 can be claimed by each passenger.
But the ECJ said the rules on board remained in place for passengers until they could leave the plane.
It said "the concept of 'arrival time', which is used to determine the length of the delay to which passengers on a flight have been subject, refers to the time at which at least one of the doors of the aircraft is opened".
The flight in question was from Salzburg to Cologne/Bonn.
The decision is binding across the EU.
EU compensation rules apply to travellers leaving from any EU airport or arriving in the EU with an EU airline or one from Iceland, Norway or Switzerland.
Compensation applicable to long-haul flights of 1,500km or more and delayed for three hours is at least €400 per passenger.
