The last recorded time a U.S. helicopter intruded into North Korean airspace was 17 years ago. On July 4, 1977, a U.S. Army CH-47 helicopter accidentally crossed the western part of the 155-mile border and was shot down.

A series of contacts between military officials took place in Panmunjom, the border village in the Demilitarized Zone, and two days later North Korea repatriated the remains of three servicemen killed and the one survivor.The incident occcurred when tensions along the border were high. One year earlier, North Korean troops armed with axes killed two U.S. officers in a tree-pruning dispute at Panmunjom.

But the North Koreans were encouraged to resolve the problem by then-President Jimmy Carter, who was working out plans to drastically cut the U.S. military presence in South Korea. That plan was later suspended.