On February 13, 2017, at 1115 eastern standard time, a Bombardier DHC-8, operated by Commutair as a scheduled flight from Fayetteville, North Carolina, to Washington Dulles International Airport (IAD), encountered turbulence resulting in a serious injury to the flight attendant. The airplane was not damaged and there were no other injuries. According to the operator, the flight was in smooth conditions during the cruise portion and initial descent. The Captain stated that as he finished the before-landing checklist at 4,000 feet, approximately 50 miles south of IAD, the flight encountered a "pocket" of moderate turbulence resulting in a descent rate of about 600 feet per minute and an altitude loss of about 400 feet. The Captain called to the cabin to check on the passengers and the flight attendant reported she injured her leg and could not walk. The flight attendant reported that she was in the final stages of preparing the cabin for landing when the turbulence occurred. Passengers assisted her until landing and paramedics met the aircraft at the gate. The flight attendant was diagnosed with a broken ankle.