Cessna Citation Sovereign (C680)
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Maintenance Action
Aircraft
Experienced unidentifiable fumes in the cockpit accompanied by light haze in cabin. Donned mask and goggles and attempted to get through checklist while expediting return to field. Requested priority handling and landed uneventfully. Crash/fire/rescue followed us to ramp and also smelled odor but could not identify the source despite a thorough inspection.
Climbing out of 10;000 [feet]; crew noticed odor and slight haze in cabin. Donned mask and diverted to departure airport while attempting to run checklist. Requested priority handling; IOE Captain took controls and landed aircraft uneventfully. Crash fire rescue meet aircraft upon landing and followed us into the ramp. Fire fighters noticed odor; but could not identify source.
CE-680 flight crew reported fumes during initial climb. Flight crew executed a return to the departure airport.