CSA ATR72 OK-GFS performing flight OK544 from Prague to Hamburg with 60 people on board was on climb out of Prague when a smoke indication rose. The crew stopped the climb and returned to Prague.
Emergency services found no fire, smoke or heat however 44 people were taken to hospital with the suspicion of smoke inhalation. They were discharged from hospital with no symptoms.
Police in Prague reported they were alerted that the ATR reported smoke from the air-conditioning.
The airline says the aircraft has been temporarily removed from service to be examined and a malfunction of the smoke detector is being suspected.