SEATTLE — Boeing said much of the design work for a major overhaul of its 777 will be done outside of its main commercial airplane base in the Seattle area.

The plan laid out in a memo to workers on Wednesday confirms suspicions that Boeing has been looking to move design work to engineers elsewher.

The company said much of the design work will be done in Charleston, S.C.; Huntsville, Ala.; Long Beach, Calif.; Philadelphia and St. Louis. Some work will also be done in Moscow.

The 777 first flew in 1994, and its one of Boeings bestsellers. It is Boeings second-biggest plane, commonly used for long-haul international flights. Boeing is expected to formally offer a revamped version for sale by the end of this year.

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The memo said no decisions have been made about how much of the new 777 will be built around Seattle. The current 777 is built in Everett, just north of Seattle.

Significant chunks of Boeings newest plane, the 787, were designed outside of Washington, and Boeing built a factory in South Carolina to assemble some 787s along with those it assembles in Everett. Boeing executives have made it clear that future design and assembly work wont automatically be done in Everett, wher the workforce is mostly unioized.