Citation Excel (C560XL)
Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 27; Flight Crew Total 6391; Flight Crew Type 145
Workload
Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Air Traffic Control Provided Assistance; Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Landed in Emergency Condition; General Evacuated; General Maintenance Action
Aircraft
Sitting in the right seat acting as Check Airman; I was performing an enroute check for a upgrading Captain. We were nearly home; overhead our final destination; ZZZ; at 3000 ft on vectors for an ILS (VMC) approach; when passengers reported a smoky haze or fog in the cabin. I could smell an oily; unburnt fuel/oil scent and looking back to the cabin behind me noticed there was a foggy haze that seemed to be increasing. As we were overhead our intended destination; we elected to get the aircraft on the ground ASAP. We donned our oxygen masks; notified ATC and were switched from Approach Control to the Tower. The Tower cleared us to land. Performing a visual short approach; we landed without incident. We taxied off the runway and stopped/shutdown on the taxiway. There was no more evidence of increasing smoke now that the engines and APU were shutdown. Of course; not knowing the reason for the fog; we immediately evacuated passengers off the aircraft and were able to secure the aircraft. Fire/Rescue equipment arrived and it was determined the was no fire risk and no further action was needed. Looking back on our response to the event; I'm glad we correctly accomplished the checklist memory items; although I will say donning the oxygen mask took more time than I expected. I had to first remove my headset; (just when I really would've liked to still be in contact with ATC); then my baseball cap and sunglasses; don the oxygen mask; switch mic sources and then put my headset back on. Taking about twenty seconds; this happened at a time where the PF (pilot flying) was making a descending 180 deg turn for a short approach and landing. Given the brief amount of time remaining before touchdown; We completed the before landing checklist. In circumspect and in talking with our mechanic and his maintenance resources; we are inclined to believe there was no fire; but an occurrence where a bearing oil seal opened inside one of the engines; (or APU); which leaked oil into a compressor section; (a source for cabin bleed air). The compressor section subsequently vaporized the oil; filling the cabin with an oily; smelly fog. The fog dissipated as we landed and reduced power. After landing we saw there was no observable damage or change to the outside of the aircraft or inside cabin; only a pervasive oily smell inside.
Aircraft was approximately 5 miles south of ZZZ at 3;000 ft MSL being vectored to the final approach course for the ILS XX at ZZZ.  Passenger approached the flight deck and reported smoke in the cabin.  PIC looked towards the cabin and observed smoke beginning to fill the cabin.  A strong odor of raw fuel also became immediately apparent.  Pilots donned oxygen mask and notified ATC.  By now the aircraft was on a left downwind leg for Runway XX at ZZZ.  Pilot made a short approach to Runway XX and landed without incident and exited the runway and shut the airplane down.
CE-560 XL flight crew reported a passenger notified them of smoke in the cabin during approach.  The flight crew completed the checklist memory items; donned their oxygen masks and landed without further incident.