Date: 201409
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: IMC
Aircraft: Citation II S2/Bravo (C550)
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ; Class C ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Recirculation Fan
Component problem: Failed
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP)
Human factors: Training / Qualification; Situational Awareness; Communication Breakdown
Anomaly: Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Crew; Person Passenger
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem; Flight Crew Landed As Precaution; Flight Crew Diverted
Contributing factors: Human Factors; Aircraft
Primary problem: Aircraft

Narrative: My right seat captain just asked if I smelled the smoke when the passengers were yelling from the rear that they had smoke in the cabin. With about a 5-10 second delay we donned the masks. In the heat of the moment it took me a second to remember switching the mask mic on while the right seat captain made gestures she could not hear me (and I was unable to hear her mic). A few seconds later she realized that her ITT button was left off after her last transmission with ATC and we finally established communications. We took a look around the cabin for any signs of smoke and looked towards the rear. At no time did we have any visual signs of smoke but a strong smell. It did not appear electrical in nature. At the time of the event we were established in cruise at FL210 in IMC; Engine Anti-Ice and Ignition was on with the RAT at 3C. ATC had just given us new instructions but we did not communicate with them. It was very difficult to communicate between us crew with the masks on; especially since with every breath the mic would activate and a roaring noise was in the ears of the other person. At times we were forced to expand the headbands to remove the masks a bit so we can talk. While the second captain was adjusting her mask and volume; I relayed to ATC that we have smoke and request a descent. After the second transmission and clarification we received an immediate clearance to descent to 11;000 ft with two options as the closest airports. We elected ZZZ1 and were cleared direct. Although efficiently handled by ATC an assigned heading with a direct clearance would have helped a lot more (and I requested it after) because we had to reprogram the FMS and scale down the MFD to have an idea which way we are going to turn. I selected a moderate descent rate of 1;500 fpm in VSI and HDG mode until we were able to both verify that the FMS was correctly setup for direct ZZZ1. During the descent we started the checklist for environmental smoke and turned off the fan. We did not change the air source since the smell of smoke started to dissipate. After about 3-4 minutes and no smell of smoke the right seat captain removed her mask to communicate clearer with ATC and brief the passengers of the status. ATC advised us that only limited equipment is available at ZZZ1 and ZZZ would be 35nm southeast of our position. We decided; based on no more smell of smoke and having better equipment available; to divert to ZZZ. While enroute we completed the regular descent and approach checklist and noticed we will be 700 lbs overweight for landing. We considered holding to burn fuel but that would have taken approx. 60 minutes. We choose to accept an overweight landing since we have good weather conditions and a long runway available. The landing was uneventful and the aircraft was turned over to maintenance to inspect for the origin of the smoke and to perform an overweight landing inspection.




Synopsis: CE550 Captain is informed of smoke in the cabin by passengers and the right seat pilot at FL210. Difficulty is encountered donning and communicating with oxygen masks on but eventually ATC is informed and a descent is requested. The Checklist for Environmental Smoke is accomplished and the recirculation fan is turned off which seems to be the culprit. Flight diverts to a suitable airport for an overweight landing.