Date: 201211
Local time of day: 1801-2400
Location: IAD.Airport, DC
Flight conditions: VMC
Light: Night
Aircraft: EMB ERJ 145 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Descent
Airspace: Class B IAD
ATC / advisory: TRACON PCT
Second aircraft: B737 Undifferentiated or Other Model
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Anomaly: Inflight Event / Encounter Wake Vortex Encounter
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Took Evasive Action
Contributing factors: Environment - Non Weather Related; Procedure
Primary problem: Ambiguous

Narrative: During descent into IAD on GIBBZ One arrival about 10 miles from GIBBZ Intersection we encountered significant wake turbulence. We were descending through 7;500 down to 6;000 FT as assigned by ATC. We noticed a hard jolt of turbulence at first that caused no attitude or roll changes. Autopilot was engaged at the time. Because we encountered some other turbulence during descent it raised no awareness as it could have been just a short pocket of turbulent air. Shortly thereafter the aircraft rolled slightly to the left about 15 degrees of bank and the autopilot corrected. As soon as we were close to wings level the aircraft rolled hard to left very quickly and we surmised somewhere around 40-45 degrees. I immediately applied significant and abrupt right rudder (but not full rudder to stops) and aileron to compensate while trying to disconnect the autopilot. As a result of overpowering the autopilot it failed and disconnected. My recovery actions were faster than my ability to disengage the autopilot which is why it failed. At the time we were doing about 245 KTS on the arrival. Upon regaining wings level I could see an aircraft lights in front of us and TCAS showed it to be about 5 miles in front and below us. We contacted ATC to find out what type aircraft we were following and that we just encounter strong wake vortices. They replied it was a B737 and that we can slow up to 230 KTS and level off at 7;000 FT if we wanted. We did both to provide some additional separation. Later while vectoring for the approach; the autopilot was reset and the fail message went away. Autopilot was reengaged with no further anomalies noted. All passengers were in their seats at the time and the seat belt sign was on. The Flight Attendant was in the galley standing at the time but was able to maintain balance and control. No further event occurred. Upon landing an explanation was provided to the passengers on why an erratic bank had occurred during flight. As a matter of precaution because of the significant and abrupt rudder input at 245 KTS; I called Maintenance Control to determine if the aircraft needed to be written for an inspection. It was unclear but he referenced some information regarding severe turbulence that discussed abrupt control movements. So we wrote the event up in the logbook as a matter or precaution so that the flight controls could be checked if warranted. The aircraft was handed off to the next crew in IAD and the First Officer who was present was debriefed. Dispatch was also debriefed on event to see if any reports were required by the crew or Dispatch. I was informed no reports were required by the crew. All checklists were complete and no further actions transpired. Separation seemed fine but I think the light tailwinds contributed to the wake remaining in our flight path during our descent.




Synopsis: An Embraer 145 Captain reports encountering wake vortices while on descent into IAD.