Gearbox comprising a fail-safe manual rotator cover

A gearbox (50) includes an outer housing (72) including manual rotation access passage (84) and a manual rotation shaft (74) coupled to a spool (34,38) of an engine (10) to rotate the engine spool. The gearbox also includes a sealing system (90, 120) coupled to the outer housing that includes a flapper valve (92, 122) that, in a closed position, prevents a lubricant from escaping from the outer housing via the manual rotation access passage.