Date: 201304
Local time of day: 1801-2400
Location: ORD.Airport, IL
Flight conditions: VMC
Weather elements / visibility: Turbulence
Light: Night
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B ORD
ATC / advisory: TRACON C90
Aircraft component: Aeroplane Flight Control
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown; Human-Machine Interface; Confusion
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Wake Vortex Encounter; Inflight Event / Encounter Weather / Turbulence
Contributing factors: Aircraft; Environment - Non Weather Related
Primary problem: Environment - Non Weather Related

Narrative: We were being vectored for a visual approach. At 7;000 FT; airspeed 170 KTS assigned and flaps at two degrees when we suddenly experienced violent vibration or turbulence. It felt like a stall but there was no PLI [Pitch Limit Indicator] and we were well above the ASI green dot. The aircraft rolled as if in wake turbulence and the First Officer either disconnected the autopilot or it automatically disconnected. The First Officer was using large aileron inputs and could not hold altitude. We started descending. I tried calling ATC but was blocked. By the third attempt to contact we were at 6;200 FT. I advised we needed lower and they cleared us to 6;000 FT. At this point things were smooth. I said we needed to get out of some-one's wake. They said the only traffic was an Airbus at 4;400 FT. I think we might have hit their wake while they were descending.This flight had been delayed because of a 'FLT Control No Dispatch' CAS message. After talking with Maintenance and resetting some systems with no effect the whole airplane was powered down. This cleared the alert. I don't know if it was a control malfunction. The event did feel like something was wrong--as in runaway trim; flutter or control surface operating incorrectly; however we had no alerts or messages during the event. It could also have been wake turbulence caused by the Airbus descending through our altitude. Upon reaching the gate we had no alerts or messages indicating a malfunction. I do not know what caused it or how it could be prevented. I have never had a situation like this. I feel the First Officer did an excellent [job] of aircraft control.


Second narrative: While being vectored for a visual approach we were at our assigned altitude of 7;000 FT and slowing to 170 KTS at Flaps 2 when suddenly the aircraft did an uncommanded roll of over 35 degrees to the left followed by a loss of altitude of over 100 FT. I immediately disconnected the autopilot and tried to regain control. The plane continued to bank hard to the left and right as well as lose altitude regardless of my input so I accepted the altitude loss.


Synopsis: An ERJ-170 flight crew suffered momentary loss of control and loss of altitude when they encountered likely wake turbulence during arrival vectoring.