Date: 201811
Local time of day: 1801-2400
Location: EVV.Airport, IN
Flight conditions: VMC
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class E MEM
ATC / advisory: TRACON MEM
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Communication Breakdown
Second reporter function: Captain; Pilot Flying
Anomaly: Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Regained Aircraft Control; Flight Crew Took Evasive Action
Contributing factors: Weather
Primary problem: Weather

Narrative: Captain was PF (Pilot Flying); and I was PM (Pilot Monitoring). Last leg of the trip; we were at 27;000 ft.; indicated at the time of the encounter. Radar was up both sides; no indication of weather ahead as we were paralleling it off to our right. We had been at FL310; descended down to FL290; no improvement; then descended again to FL270. We had been there for approximately 15 minutes with continuous light-occasional moderate chop. Around KEVV we experienced sudden erratic severe turbulence for the better part of 60-90 seconds. The airplane instantly went into an over speed condition for about 30-45 seconds; even with PF bringing the thrusters to idle immediately. I do not know how high the airspeed went; but we were in the red for about half of the time. As I was attempting to contact Memphis Approach with no avail due to radio congestion; we made the decision to start a descent without clearance. Once I was able to get through I told ATC about the turbulence we encountered; and they cleared us to descend. As we were descending; the turbulence was continuing so I asked for a left hand turn. Once we got to FL240; and a heading of around 020 we exited the conditions. There had been no reports ahead of such turbulence when I checked in prior to the encounter. I called up the flight attendants immediately to make sure that they were not injured and made sure the passengers were uninjured also. Then made a PA announcement to the passengers to reassure and ask the flight attendants to be seated for the remainder of the flight.


Second narrative: We were filed at FL310. Upon reaching FL310 we encountered continuous light to moderate chop. ATC recommended lower for better rides so we descended to FL290. That ride was good for about 10 minutes and the next controller advices 'no complaints' at FL270. Got numbers from Dispatch and descended to FL270. FL270 was smooth; the seatbelt sign was turned OFF for about 30 minutes when out of nowhere we encountered severe turbulence (PIREP from ATC after our report said it was over EVV). The plane climb/descended +/- 600 and banked Left/Right 10 to 15 degrees while we [were] overspeed to 330-340 knots. We tried to inform ATC we needed to descend but they were talking to another aircraft about weather along their route. We tried 2-3 times to get a word in before I decided to start a gradual descent to a lower altitude while we tried talking to ATC. Once we did get a word in (at about FL264) we were cleared to FL240 and were asked if we had any injuries. We did not and continue our flight at FL240.


Synopsis: EMB 170 flight crew reported encountering unreported severe turbulence.