Passengers on a flight arriving at Chicago's O'Hare Airport said they were sent down evacuation chutes amid concerns something was wrong with the plane. American Airlines said the crew of Flight 4309 noticed an instrument that warned of a possible issue with the aircraft after it landed about 5 p.m. CST Monday. The captain then ordered a precautionary emergency evacuation, WBBM-TV, Chicago, reported. No other details were given. The travelers aboard the American Eagle flight, who had come from Washington, D.C., said they were about to get off the Embraer E175 when they heard someone say "Evacuate!" All 57 passengers and four crew members were then sent safely down the evacuation slides. No serious injuries were reported, WGN-TV, Chicago, reported.