Screening snafu clears O'Hare concourse

Transport Department: As many as 20 flights affected

CHICAGO (CNN) -- A security screening machine malfunctioned Monday, forcing the evacuation of a concourse in Terminal 3 at O'Hare International Airport.

THE SYSTEM Airport security: A system driven by the minimum wage PREVIOUS WARNINGS Warnings over airport security preceded attacks COMPARING U.S. TO EUROPE Outside the U.S., a different approach to air security SOLUTIONS Boosting security puts focus on government's role  GRAPHS & CHARTS  • Top 25 Airports  • Airport Security by Year  • Airline Security by Year  • Airport Wages

The evacuation was ordered around 8:45 a.m. CST (9:45 a.m. EST), when security personnel determined that a magnetometer -- the device passengers walk through at security checkpoints -- wasn't working.

About 30 minutes later, after being rescreened, passengers were allowed to return to the concourse.

Monique Bond, a spokeswoman for the Chicago Department of Aviation, said authorities didn't know why the device malfunctioned.

She couldn't say how many flights were delayed or how many passengers had been affected by the evacuation. But she said the concourse was quite crowded with waiting passengers.

An official with the United States Transportation Department in Washington said 17 American Airlines flights and 3 Delta Air Lines flights were affected.