Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor
Flight Crew Last 90 Days 50; Flight Crew Total 8600; Flight Crew Type 25
Distraction; Workload
Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Provided Assistance; Flight Crew Regained Aircraft Control; Flight Crew Took Evasive Action
Weather
Level at FL350 en route we were on a vector from ATC to avoid the area of buildups ahead of us. We were in instrument conditions when we started to encounter severe turbulence with downdrafts that decreased our altitude to about 34;650 FT on the altimeter. I was going to disconnect the autopilot; but the PIC advised against it and said to let it ride it out and then he informed ATC that we were unable to maintain our RVSM assigned altitude of FL350. ATC then assigned us a block altitude of FL340-350 and advised us we should be exiting the weather soon. Our onboard weather avoidance equipment did not show any activity at our altitude and position and because of the IMC conditions we were unable to visually locate any activity. Shortly thereafter we exited the weather in to VFR conditions.
One minute severe turbulence; altitude variations up to 400 FT; advised ATC unable to maintain RVSM separation and requested /received clearance to deviate 30 degrees left to avoid turbulence area. Turbulence stopped after one minute and normal operations resumed; no other problems noted.
A CE-501 encountered severe turbulence for one minute at FL350 and advised ATC they were unable to maintain RVSM because of altitude variations up to 400 FT.