Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter Wake Vortex Encounter
Air Traffic Control Issued New Clearance; Flight Crew Took Evasive Action
Environment - Non Weather Related; Procedure
On the DIRTY2 arrival level at 12;000 FT and 250 KTS we felt a few bumps on what had been a smooth ride up until then. A few more bumps occurred that were comparable to light chop. We queried ATC if there was an aircraft in front of us. They told us there was a B737 [or B757] ahead at the same altitude. About the same time the aircraft rolled about 10 degrees or so to the left and came back to level. Then about 20 degrees or so right bank and corrected. Another roll brought us even further over; I'm guessing over 30 degrees to the right and corrected. The autopilot was engaged and was making very rapid control movement beyond what I have seen before. I disconnected the autopilot at that time and hand flew through another roll or two while the pilot not flying requested a heading off of the arrival to get out of the wake turbulence. During the hand flying in the turbulence and [while in the] 20 [degrees] right [turn] ATC heading the aircraft got off altitude 100 FT high. This was quickly corrected and automation was re-established. The ride improved as soon as we were vectored off the arrival course. ATC then brought us back to the arrival and we landed without further incident.
First Officer returned to assigned altitude and pilot not flying reengaged autopilot.The preceding aircraft's turbulence was a threat; and pilot not flying should have been quicker to notify ATC. There was some frequency congestion; but deviating off the assigned altitude by 100 FT was an error both by pilot flying and pilot not flying. Pilot not flying should have been more vigilant; but was distracted making the call to ATC.
CRJ-200 flight crew reported encountering wake turbulence that resulted in rolls to left and right while in trail of a narrow body Boeing during arrival to ATL. ATC provided a turn off course.