A faulty network card forced the closure of Dublin airport last week as air traffic control was unable to track the location of incoming planes.

The airport was shut on 16 July as plane tracking was lost for up to 10 minutes at a time. Flights had to be rerouted across Europe, causing widespread delays.

The problem has been traced to a faulty network card that caused the system, built by Thales, to overload.

"Thales ATM confirmed the root cause of the hardware system malfunction as an intermittent malfunctioning network card which consequently overcame the built-in system redundancy," said the Irish Aviation Authority in a statement.

"Thales ATM also confirmed that the cause of the malfunction was the same for previous malfunctions which had occurred since 2 June 2008.

"Thales ATM stated that in 10 similar air traffic control centres worldwide with over 500,000 flight hours (50 years) this is the first time an incident of this type has been reported."

The radar system had been suffering problems for some time and the airport was allowing fewer planes to take off and land.

By Wednesday at around 2pm Dublin air traffic control lost all height and location information on flights and ordered aircraft into a holding pattern before dispersing them to other landing spots.

Dublin is Ireland's busiest airport and the closure caused serious disruption to passengers and airlines.