Date: 201209
Local time of day: 0601-1200
Location: ZME.ARTCC, TN
Flight conditions: VMC
Light: Dawn
Aircraft: Regional Jet 200 ER/LR (CRJ200)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Descent
Airspace: Class E ZME
ATC / advisory: Center ZME
Second aircraft: B737 Undifferentiated or Other Model
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Situational Awareness; Distraction
Anomaly: Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; 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; Chart Or Publication; Procedure
Primary problem: Environment - Non Weather Related

Narrative: ATC had cleared us to descend via the FNCHR1 arrival. We descended as prescribed; following the snowflake down. At approximately 16;000 FT and somewhere near FNCHR; we encountered severe wake turbulence from the B737 that was also descending via the FNCHR approximately 10 miles in front of us. The aircraft was tossed around so much that I disengaged the autopilot in an attempt to level us off and fly the aircraft above the flight path of the preceding aircraft; as I believed that we had descended into it (at this point we were slightly below the snowflake). This course of action did not seem to help as we were continuing to be tossed around quite severely. The Captain then suggested that we descend out of it. So I pushed the nose forward and attempted to fly below the preceding aircraft's flight path. This did not seem to help either. After what seemed like an eternity (Flight Attendant estimated approximately 2-3 minutes) we finally decided we'd had enough and requested 10 degrees left of course so as to laterally deviate away from the other aircraft's flight path. ATC cleared us to deviate and as we did the wake turbulence ceased to affect us.The preceding aircraft's wake turbulence was a threat. On this particular morning the winds at this altitude were calm; which was also a threat. 'Descend via' procedures exacerbated the threat; as they put us in much closer proximity to the other aircraft's flight path. As the preceding aircraft was 'heavy; clean; and slow (250 KTS);' the wake turbulence was much more severe than would be encountered on a typical ILS approach. I do not believe that we had a lateral deviation. A vertical deviation may be more likely; as I was initially more concerned about flying above the other aircraft's flight path than away from it. Because we were descending on a prescribed flight path; we were essentially required to be at the same point in space as the preceding aircraft (to meet crossing restrictions). If the snowflake is not followed on this descent; then you will be high (above 16;000) at FNCHR. Therefore; unless we had descended much more rapidly (below the snowflake) there was pretty much no way of avoiding the other aircraft's wake turbulence (as he was descending as prescribed as well). 10 miles separation seemed appropriate; but given the lack of wind at altitude; the wake turbulence apparently lingered longer than normal. In the future; I will be much more aware of a potential wake turbulence encounter on a 'descend via' procedure. Additionally; I will try to not fly below the snowflake unless I absolutely have to or to descend much below it (as long as I am able to meet a crossing restriction). I believe that the company needs to make other crew members aware of the increased potential for a wake turbulence encounter when cleared to 'descend via.' Because of this potential; it is highly advised that the approach be briefed and all other non-essential items be completed before the descent so that the pilot flying can pay much more attention to the aircraft's flight path and can react more quickly to an inadvertent wake turbulence encounter.




Synopsis: A CRJ-200 descending via the FNCHR RNAV STAR to MEM in calm wind conditions experienced what the flight crew believed to have been long term severe wake turbulence from a preceding aircraft.