The wing of a departing jetliner struck the tail of another plane on a holding pad at O'Hare International Airport during a severe thunderstorm, authorities said.
No injuries or fuel spills were reported.
Chicago Department of Aviation spokeswoman Wendy Abrams said the accident occurred about 3:50 p.m. Wednesday when the wing of a taxiing United Airlines B777 struck the tail of a stationary American Airlines MD80.
The United plane appeared undamaged and taxied back to the gate a short time after the collision, but American spokeswoman Mary Frances Fagan said the American plane suffered damage to its rudder and remained on the holding pad for about an hour before returning to the gate.
Fagan said American Flight 1817 was carrying 136 passengers and five crew members and had been scheduled to depart for Seattle.
United spokesman Jeff Kovick said United Flight 149, bound for San Francisco, was carrying 347 passengers and a crew of 11.
Fagan and Kovick said the airlines were working to get the stranded passengers out on later flights.
Tony Molinaro of the Federal Aviation Administration said his agency was investigating the accident and had notified the National Transportation Safety Board. Molinaro said aircraft operators are responsible for maintaining their distance from one another on the holding pad.