Date: 201404
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Citation Excel (C560XL)
Operator: Fractional
Operating under: Part 91
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Takeoff / Launch
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Air Conditioning and Pressurization Pack
Component problem: Malfunctioning
Reporter organization: Air Taxi
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Physiological - Other; Troubleshooting; Distraction
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Maintenance; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Became Reoriented; Flight Crew Took Evasive Action; Flight Crew Returned To Departure Airport; General Maintenance Action
Contributing factors: Human Factors; Procedure; Environment - Non Weather Related; Aircraft
Primary problem: Ambiguous

Narrative: Departed and we noted a strong toxic chemical smell on departure. We continued the climb thinking it would burn off as we picked up the plane from maintenance. We continued the climb and the smell lessened; but continued. We attempted to contact the company with the iPhone; but that did not work. We leveled at 23;000 and continued to smell the odor though not nearly as strong. We decided to return to the departure airport; at that time we donned the oxygen masks. There was no smoke; and the smell was not a hot smell. The temperature of the ducts was cool the entire time and the cabin was also cool. We landed without incident. One of the mechanics met us and we asked him to step inside the cabin and smell the interior. He noted a chemical smell. After we had landed I noted my nostrils were burning. I went and asked the PIC if his burned also; he said they did. I decided to go to the doctor and have them give me a check up. They did not find any serious issues though they asked several times what could have been burning. I could not tell them as I didn't know. Something definitely was leaking into the air system. This was a repeat write-up; and both the PIC and I were not aware of this. It was in the logbook; we failed to review the past write-ups in depth. A thorough review of what was done to the aircraft during maintenance is a step we missed and should not have. Electronic logbooks would make this easier for both the PIC and SIC to review. As I spoke with the mechanics they thought it might be residual burn off from the repairs made. Why was this aircraft not run at a high power setting to burn it off before we were supposed to take it to 40;000? We were complacent in thinking the smell would burn off (I can understand this in some situations-like de-ice where you can identify the smell) and we did not know where the smell came from. We should have donned the masks and returned shortly after takeoff when we first noticed the toxic chemical smell.




Synopsis: A CE-560XL crew picked up an aircraft from maintenance and during takeoff noticed a strong toxic chemical odor; so after donning oxygen masks they returned to the departure airport. Medical tests were inconclusive and the odor's source not determined.