A Chinese airport temporarily closed on Tuesday amid fears that one of the passenger planes could collide with an unidentified flying object that was seen in the area.
Flight delays happen for many reasons. Airlines can impose delays on themselves, or when weather hits, delays are put into place by air traffic control.
A small fire broke out in the cockpit of a United Airlines flight to Los Angeles about 30 minutes after taking of from New York JFK Sunday evening, forcing the Boeing 757 to make an emergency landing at Washington Dulles.
Poland has announced that it will conduct its own probe to determine the causes of last year's plane crash in Russia, which killed 96 people including Polish President Lech Kaczynski.