Date: 201907
Local time of day: 1201-1800
Location: ZDC.ARTCC, VA
Flight conditions: VMC
Weather elements / visibility: Thunderstorm
Light: Daylight
Aircraft: Citation Excel (C560XL)
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Cruise
Airspace: Class A ZDC
ATC / advisory: Center ZDC
Reporter organization: Corporate
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown
Second reporter function: Captain; Pilot Flying
Anomaly: Deviation - Altitude Excursion From Assigned Altitude; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Took Evasive Action; Flight Crew Became Reoriented
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: We were level at FL200 on autopilot. I was PNF (Pilot Not Flying). We were heading toward an area of rapidly building thunderstorms. PF (Pilot Flying) was using the autopilot in heading mode and was heading toward an area building pretty rapidly. I told him as we got closer I didn't think it was a good idea to go that way. He had gotten so close to the area that he couldn't just use the autopilot to make the turn so he pushed the TCS (Touch Control Steering) switch and increased bank. Before I could say anything bank angle was over 40 degrees and we were descending. He was trying to regain altitude but was not aggressive enough and ended up down 500 ft. It happened again another time and he gained altitude this time but only about 200 ft. Just as we were coming back to FL200 ATC asked about altitude. I said we had descended as we were maneuvering away from the cell but were back at FL200. Nothing else was said by ATC.I think folks get way too dependent on the autopilot. He got much too close to turn and avoid the cells using heading mode on the autopilot. When he pushed the TCS switch to fly manually he failed to arrest the descent. If he had started the turn earlier the autopilot would have turned just fine but once he saw he was too close he needed to just switch off the autopilot rather than pushing the TCS switch and fly the airplane. I think pushing the TCS switch distracted him. I also think it would be a good idea to have better cockpit communication. We were level and I was doing paperwork. He was deviating around the weather. I assumed he'd find a good path but we didn't talk about what he was thinking. I was of the opinion that we needed to deviate further but he was looking at an area that he thought would be clear. However; even if that area had been clear; by the time he could determine it was clear he would have had no other option. He would have had to go that way because he was going between two very close obvious cells. While we could have deviated farther left (which is what we ended up doing) without an issue. I will make sure we work on communication because I think better communication would have eliminated the need for the tight turn and eliminated the altitude deviation.


Second narrative: We were deviating around a large area of rapidly building thunderstorms. I was flying toward an area of clouds where I thought there would be a break in the clouds to our right. When I realized there was not a break; I was too close to the storm and had to make a hard 90 degree turn to the left at a steep bank angle. During the turn; I descended approximately 500 ft. before climbing back up to FL200. It was poor judgment on my part.


Synopsis: CE-560XL flight crew reported an excursion from assigned altitude caused by an attempt to avoid weather coupled with a communications breakdown.