China Southern Airlines (CZ, Guangzhou) says it has agreed to sell its four remaining B777-200s back to Boeing (BOE, Washington National) in line with plans to phase out the type, along with the B737-300 and B757-200, from its fleet by 2021.

A filing with the Shanghai Stock Exchange indicates the four remaining widebody jets, along with two spare GE90-85B engines, will be returned to the US manufacturer over the course of 2017 and 2018.

In addition to the twelve B787-9s it has ordered from Boeing, China Southern says it has also reached agreements with AerCap and Air Lease Corporation to lease three and five more of the type respectively.