EMB ERJ 170/175 ER/LR
Flight Crew Air Transport Pilot (ATP)
Flight Deck / Cabin / Aircraft Event Illness / Injury; Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Wake Vortex Encounter
Air Traffic Control Issued New Clearance; Flight Crew Took Evasive Action; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Regained Aircraft Control; General Physical Injury / Incapacitation
Environment - Non Weather Related; Procedure
[We were cruising] at FL350. The aircraft abruptly banked left 50-60 degrees with no warning. The autopilot was on and we were in VMC conditions and smooth air. Both the Captain and myself grabbed the controls and regained control of the aircraft; bringing the wings level. The autopilot was disconnected in this process. We notified ATC of the event and asked if we were behind any heavy aircraft. ATC informed us that we were 9 miles in trail of a B777. We lost roughly 1500 feet during the event but we were already cleared to descend to FL270 at our discretion to cross a fix at that altitude. We coordinated with ATC to continue our descent early and slow the aircraft to increase separation with the heavy B777 in front of us. A few minutes later we were passed to Approach Control. After we checked in with Approach Control the aircraft again abruptly banked to the left roughly 20-25 degrees. We informed ATC of this additional event and asked for an off course vector to get away from the B777 in front of us. The flight was then completed normally.Two passengers were injured in the cabin but refused treatment. FA1 was injured by a galley cart. The Captain coordinated with operations and asked for a customer service manager [and] paramedics to meet us at the gate. Paramedics cleared both passengers and the flight attendant was taken to the hospital for observation.Increase separation behind heavy aircraft to avoid wake turbulence.
[Report narrative contained no additional information.]
EMB-175 flight crew reported two wake turbulence encounters inbound to IAD in trail of a B777 that resulted in 'abrupt' rolls and loss of altitude.