Incident Overview
On November 30, 2010, at approximately 0935 central standard time, an Embraer EMB-135LR, registration N12530, operated by Chautauqua Airlines Inc. as Flight 1146, encountered turbulence while in cruise about 60 miles south of Milwaukee, Wisconsin. The flight was a scheduled domestic passenger operation under 14 Code of Federal Regulations Part 121. Instrument meteorological conditions prevailed with an activated instrument flight rules flight plan.
Flight Details
The flight departed from Lambert-St Louis International Airport (STL) near St Louis, Missouri, at about 0902, and landed at General Mitchell International Airport near Milwaukee, Wisconsin, at about 1002. The two pilots and 17 passengers were uninjured. The flight attendant sustained a serious injury, and nine passengers sustained minor injuries. The airplane sustained no damage.
Preflight and In-Flight Conditions
The dispatch package included remarks for SIGMET VICTOR 1, valid until 1130, covering parts of Iowa, Wisconsin, Michigan, Illinois, and Indiana, with occasional severe turbulence between 14,000 and 24,000 feet MSL. The dispatcher issued the flight with a cruise altitude of 13,000 feet MSL and a remark to lower flight level due to turbulence. Air traffic control in STL discussed the potential for turbulence with the flightcrew, suggesting 15,000 feet MSL as a better option, though turbulence might still occur. The captain changed the cruise altitude to 15,000 feet MSL. The crew announced that the seat belt sign would remain on for the flight.
Turbulence Encounter and Injuries
During the flight attendant's service, the aircraft experienced light turbulence initially, then moderate turbulence about halfway through service. The flight attendant locked the cart and took a seat. The moderate turbulence dissipated after about one minute, and she completed the service. Following service, while standing by the forward wardrobe closet, she was thrown up into the ceiling and back to the floor, breaking her nose and fracturing her left wrist. After the turbulence encounter, the flightcrew contacted the flight attendant to inquire about her condition and that of passengers. She reported three passengers who had bumped their heads on overhead passenger service units and informed the crew of her injuries. Medical personnel were requested and met the aircraft at the gate.
Flight Data Recorder Information
According to flight data recorder data, at approximately 0935, while cruising at a pressure altitude of about 15,230 feet with an indicated airspeed of 317 knots, the airplane's vertical acceleration increased from 1 g to 1.3 g's. About 0.25 seconds later, acceleration decreased to -1.2 g's. About 0.63 seconds later, it increased to 1.8 g's, then about one second later decreased to 0.4 g's. During the upset, pressure altitude reached a maximum of 15,407 feet and indicated airspeed increased to 329 knots. Approximately 15 seconds later, vertical acceleration settled back to 1 g.
Post-Incident Observations
A Federal Aviation Administration (FAA) inspector confirmed that all passenger seat belts were fastened. A seated five-foot nine-inch passenger was observed to have a six-inch gap between the overhead passenger service unit and the passenger's head. Three passenger service units sustained damage consistent with passenger head impacts. None of the passenger lap belt restraints had failed. Nine passengers reported minor injuries.
Operator Response
Subsequent to the incident, the operator published an article on turbulence in the airline's quarterly safety newsletter for all employees. Additionally, the operator produced a memorandum on turbulence and the incident focused on flight operations personnel.