Compensation in the EU after technical problem after take off

Under EU Flight Compensation Regulation 261, you are entitled to compensation if your flight is delayed by more than a certain amount of time. In 2009, the European Court of Justice ruled that this delay applies to the "loss of time" experienced by the passenger; in other words, it's calculated as a delay of the arrival time, not the departure time. A 2014 CJEU ruling clarified this further: the delay is calculated between the scheduled arrival time and the time at which the aircraft doors open at your final destination.

Thus, passengers on a flight that was diverted or returned to its departure point would be entitled to compensation, rerouting, refunding, and/or overnight accommodation. This assumes, of course, that the length of the delay met the pertinent thresholds, and that the diversion/return was not due to meteorological factors or air traffic management.

If you are on an EU-regulated flight, the delay was the airline’s fault, and you arrived 3+ hours late at your destination, you’re entitled to compensation. Depending on the circumstances of the delay, you’re entitled to other compensation eg accommodation if the delay is overnight. This article provides some further relevant information. https://www.moneysavingexpert.com/travel/flight-delays