The Japan Airlines plane was being towed at roughly 6 p.m. when a member of the Boeing ground crew was run over, according to Paine Field Airport director Dave Waggoner.
The man was trapped for a time, but crews were eventually able to get him out from underneath the plane.
After being rescued, a helicopter transported the crew member to Harborview Medical Center to be treated for leg injuries.
The man's condition is listed as "serious."
In a written statement, Boeing's Elizabeth Fischtziur said she wouldn't speculate on what caused the incident.
"Our deepest concern and focus right now is for the welfare of the injured employee and his family," the statement reads. "We are in contact with them and are offering whatever assistance they may need."
Fischtziur said the company will investigate the incident and will "implement the necessary changes to avoid a future reoccurrence."