German federal police on Monday arrested a 62-year-old Spanish man suspected of entering the security area of Terminal 1 at Cologne-Bonn airport without being checked, a spokeswoman said.
The breach led police to clear the security area of the departure floor in Terminal 1 at 12:15 local time (10:15 GMT) and to ground five planes in their parking positions, the airport said.
The airport reopened the security area at 13:30 local time (11:30 GMT) and said operations were returning to normal at Terminal 1 but some departures were delayed.
It said no planes took off or landed at that terminal while the security area was closed, though operations continued as normal from Terminal 2.
The man arrested wanted to take the quickest route to the Faro-bound plane he was due to board, the police spokeswoman said, adding that he was still being questioned.
Cologne-Bonn airport said in a statement that a person had apparently entered the security area without being checked.
In March a policewoman in plain clothes managed to get into one of the terminals without being checked, leading to the building being cleared.
Concern over security has grown at European airports since March 22, when three suicide bombers killed 32 people in Brussels in attacks that shut down the airport.
Islamic State has posted pictures on the Internet calling on German Muslims to carry out Brussels-style attacks in Germany such as at Cologne-Bonn airport, the SITE intelligence group reported in March.
Last month, German broadcaster ZDF said a confidential emergency plan for Cologne-Bonn airport was posted on its website for several months.