HONG KONG (Reuters) - China Eastern Airlines Corp Ltd <0670.HK> said on Monday it has agreed to buy 20 new Boeing B777-300ER aircraft from Boeing Co , valued at $5.94 billion based on the 2011 price catalog.

In a filing to the Hong Kong bourse, China Eastern said the aircraft were expected to be delivered in stages from 2014 to 2018.

Boeing said on Friday that China Eastern Airlines had agreed to buy the 20 aircraft, pending Chinese government approval.

The Chinese carrier also said it would sell five Airbus A340-600 aircraft, with an unaudited book value of about 4.47 billion yuan ($708 million), to Boeing.

China Eastern said the A340-600 aircraft, which mainly serve long-haul international routes such as Shanghai-to-New York and Shanghai-to-Los Angeles, had high operation costs and relatively weak route competitiveness.

The Airbus aircraft began service in 2003 and 2004 and had an average usage of about 8.3 years.

China Eastern said the purchase of the Boeing aircraft and disposal of the Airbus planes would lower its unit operation costs and optimize the fleet structure for long-haul air transportation routes.

For a statement click http://www.hkexnews.hk/listedco/listconews/sehk/2012/0430/LTN20120430006.pdf

China Eastern Airlines posted a 73.7 percent fall in net profit for the first quarter of 2012 to 266.5 million yuan.

($1 = 6.3102 Chinese yuan)

(Reporting by Donny Kwok; Editing by Richard Pullin)