South Korea has begun a second day of national mourning after a Boeing 737-800 airliner operated by Jeju Air skidded off the end of a runway at Muan International Airport and crashed into a concrete wall before bursting into flames, killing all but two of the 181 people on board. It was the worst aviation disaster involving a South Korean airline in nearly three decades. Investigators are looking into whether a bird strike caused the flight from Bangkok to crash, and why the pilots did not have the plane’s wing flaps or landing gear deployed when attempting an emergency landing.