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.
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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.