What was found
AIRCRAFT WAS GROUNDED: NOSE GEAR DOOR WOULD NOT COME UP AFTER TAKE OFF, POSSIBLY ALSO GEAR. EMERGENCY DECLARED. PUT GEAR BACK DOWN, RECEIVED A SAFE INDICATION AND LANDED SAFELY WITHOUT FURTHER INCIDENT. MAINTENANCE SERVICED OIL AND NITROGEN PER MM 32-21-02 AND REPLACED NITROGEN SERVICING VALVE AND ACCOMPLISHED NOSE GEAR RETRACTION/EXTENSION CHECK, TAXI CHECK OF NOSE STRUT, AND PERFORMED SUCCESSFUL OPERATIONAL CHECKS, NO LEAKS NOTED.