SEOUL, May 8 (Reuters) - Korean Air will

sell five of its planes to U.S. aerospace firm Sierra Nevada

Corporation, the airline said in an exchange filing on

Wednesday.

Sierra Nevada recently won a $13 billion U.S. Air Force

contract to develop a successor to the E-4B Nightwatch, known as

the Doomsday plane due to its ability to survive a nuclear war

and act as a command and control centre during emergencies.

Sierra Nevada did not immediately respond to a request for

comment.

The Korean Air planes being sold are four-engined Boeing

747-8s, a source familiar with the matter said.

The four current E-4 planes, which have been in service

since the 1970s, are modified Boeing ( BA ) 747-200s.

The sale, valued at 918 billion Korean won ($674 million),

is in line with Korean Air's medium to long-term plan to dispose

of older aircraft and replace them with newer generation ones,

the Korean Air filing said.

Korean Air will have delivered the planes by September 2025,

the filing said.

($1 = 1,363.0100 won)