Parts of Frankfurt Airport were evacuated on Tuesday and dozens of flights cancelled after a French family of four got past security despite a positive test for explosives.
Police blamed “an error by a security officer”.
It led to boarding being halted and a partial evacuation of Terminal 1.
The family were later found, questioned and allowed to travel on. A police spokeswoman said one of them had not fully completed security checks.
Police did not clarify what had triggered the positive explosives test.
A similar incident on 28 July at Munich Airport caused 300 flights to be cancelled, affecting 30,000 people.
Travellers at Frankfurt Airport – Germany’s largest – are now facing cancellations and long queues to re-enter the departure area. More than 49 flights have been cancelled, German media report.
Passengers earlier complained of confusion and lack of information during and after the evacuation.
“If this continues, we will miss the next flight,” a Belgian passenger told Frankfurter Allgemeine from the end of a security queue, after obtaining a ticket for a second flight.
Around 1,500 flights were set to take off or land at Frankfurt airport on Tuesday.
German airliner Lufthansa, which has its main hub at the airport, said it was working on a new flight plan and would update passengers as soon as possible.
German police defended the evacuation on social media, saying they had to exclude any and every risk.