On Tuesday of this week, the pilot of a US Airways jet in landing mode at Philadelphia International Airport reported an unknown object whizzing by his plane. The airport was closed for half-hour to be sure no further security actions ought to be taken.
The FAA and the FBI are investigating. Official statements say the article might have been a flare launched from the bottom, but an investigation by the Philadelphia Police turned up nothing.
See a whole report with video at Another UFO Near Miss on Landing Jet in Philadelphia , and comment as you prefer.