Medium Transport; Low Wing; 2 Turbojet Eng
Flight Crew Air Transport Pilot (ATP)
Workload; Time Pressure; Situational Awareness
Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Weather / Turbulence
Flight Crew Regained Aircraft Control; Flight Crew Returned To Clearance; Flight Crew Took Evasive Action; Flight Crew Became Reoriented
Weather
We were flying at FL410 on a ferry leg. The radar was on and we were monitoring the weather ahead. We had discussed routing to avoid the large cells ahead and had placed the seatbelt on so that the flight attendant would be seated in case of rough air. We had deviated to the south of our original route and were approximately 20 miles south of the large cell. As we approach the area we commented on how steep the gradient was on the radar return. Additionally we noted that we were up wind of the cell with the wind out of the south at approximately 30 to 40 kts. We were well south of the radar returns when we encountered moderate to severe turbulence. At the onset of this event I saw the nose yaw rapidly to the left; the nose began to rise and the aircraft started [to] gain altitude. I disengaged the autopilot but was unable to initially control the pitch. The aircraft rolled rolled left in a 20 to 25 degree angle but I was able to easily correct the bank angle. Before I was able to regain control of the pitch the aircraft climbed almost 600 ft. The captain informed ATC of our situation and requested a block altitude and was granted FL390 to FL430 for the area that we were in. Shortly after we were able to regain control of the pitch and level the aircraft at FL410. Other than the cell off to the left of the aircraft we had no other returns on the radar. The duration of this event from start to finish was approximately 60 seconds. While we followed standard thunderstorm avoidance guidance in this case it was not enough separation. We were prepared for some rough air but not an upset at 41000 ft. It would perhaps be beneficial for upset training to be conducted at high altitudes to include high altitude stalls at or near aircraft service ceilings.
Turbulence induced altitude deviation during cruise at FL410 we were deviating around radar depicted cells in IMC conditions. We passed to the south of the clearly depicted edges of a cell on the upwind side by approx 20nm. We experienced moderated to severe turbulence for about 20 seconds during which the aircraft was pushed up 600 ft from our assigned altitude; angles of bank exceeded 25 degrees; yaw changes 15 degrees side to side occurred; and the autopilot disconnected. We notified and coordinated with ATC; received clearance for block altitude FL390-FL430 and then returned to our assigned altitude of FL410 when conditions permitted. We notified ATC we were thru the turbulence event and continued to our destination. The flight attendant was seat belted and uninjured nor were any discrepancies in the condition of the aircraft noted on post flight. We appeared to be at a recommended safe distance and upwind on passing the cell. We maintained pitch attitude and airspeed during the event to minimize stresses on the aircraft.
A Fractional Jet Crew described a moderate to severe turbulence encounter at FL410 which resulted in an uncontrolled 600 ft altitude increase upwind and 20 miles from the nearest cell.