A plane of the South Korean airline Jeju Air at Seoul Incheon International Airport.Benard /Andia/Universal Images Group/Getty ImagesBoeing stock fell as much as 6% after a Jeju Air plane crash in South Korea over the weekend.The crash involved a Boeing 737-800, killing 179 of 181 on board.Investigations into the crash are focused on a potential bird strike and landing gear failure as causes.Boeing stock declined as much as 6% on Monday following a plane crash in South Korea over the weekend.A 15-year-old Boeing 737-800 plane operated by Jeju Air, a Korean budget airline, crashed Sunday morning after it overran the runway at Muan International Airport.The crash killed 179 of the plane's 181 passengers and crewmembers.Authorities in Korea believe a bird strike could have been a factor in the fatal crash.