Security screeners at a US airport lost track of a bag containing fake explosives and allowed to be loaded on a flight to Amsterdam.
US airports stepped up security after the 11 September attacks
The "bomb" was planted in luggage for training exercise at Newark Liberty International Airport.
A scanning machine raised the alarm, but the bag was not searched and airport staff lost track of it.
"At no time did the bag pose a threat and at no time was anyone in danger," said a transport security spokeswoman.
Only two weeks ago, Paris airport staff lost plastic explosives slipped into a random bag for sniffer-dog training.
France was forced to alert dozens of airlines to warn them the explosives might be aboard after the hold-all was loaded on to any one of 90 flights.
Detonator and clock
In Newark, the bag containing the fake device - complete with wires, a detonator and a clock - was not found despite an hour-long search.
It was later recovered by security officials in Amsterdam.
The airport near New York City was one of three used by the 11 September hijackers.
A spokeswoman for the Transportation Security Administration, the agency responsible for screening baggage and passengers, said the incident showed the importance of training exercises.
Airport screening in the US has been stepped up since the 11 September attacks but undercover inspections have revealed some weaknesses.