(CNN) -- Two planes made emergency landings at Amsterdam Schiphol Airport at almost the same time Monday, the Dutch airport said.
The first plane was a KLM flight departing en route to Milan, Italy. The flight reported a possible technical problem and asked to return.
The plane was inspected by engineers, and passengers were waiting to depart, the airport said.
The second emergency landing involved a Delta Air Lines plane.
It was not immediately clear what prompted that plane to land.
Initially, the airport said a fire caused the landing. But a military police official described the issue as one of "technical difficulties."
Delta would only say the plane, from Amsterdam to Mumbai, made the landing for "precautionary measures."
"The aircraft landed without incident, and passengers deplaned normally," the airline said in a statement.
It was "nothing big," Robert Van Kappel of Schipol Military Police of the incident.
Schiphol is one of Europe's busiest transit sites.