N942AC

On August 2, 2015, at 1437 central daylight time, a Cessna 208B, N942AC, operating as Air Choice One (call sign Weber) flight 2627, was substantially damaged when a wind gust lifted it up and it impacted the taxiway while awaiting takeoff clearance at Chicago O'Hare International Airport (ORD), Chicago, Illinois. The two flight crewmembers and five passengers were not injured; two passengers sustained minor injuries. The airplane was registered to and operated by Multi-Aero, Inc., under the provisions of Title 14 Code of Federal Regulations Part 135 as a scheduled domestic passenger flight. Day visual meteorological conditions (VMC) prevailed, and an instrument flight rules (IFR) flight plan had been filed. The airplane had departed the terminal gate at 1410 and was destined for Southeast Iowa Regional Airport (BRL), Burlington, Iowa.There had been numerous reports of wind shear and microbursts in the immediate vicinity. According to the captain and first officer's statements, they were awaiting takeoff clearance on runway 22L when the control tower asked that they move aside to allow other aircraft to pass. As the captain was making a right turn, a wind gust lifted the right side of the airplane and turned it clockwise. The airplane remained nose down, resting on its left wing for several seconds, then fell back upright coming to rest on all three landing gears. The engine was secured, and all occupants deplaned through the main cabin door. A post-accident examination showed the outboard portion of the left wing was bent up about 30 degrees, the left aileron was damaged, and all three propeller blades were impact damaged.

According to a special weather study conducted by the National Transportation Safety Board, the National Weather Service's (NWS) Surface Analysis Chart valid at the time of the accident depicted a low pressure system over northwestern Michigan, with a cold front extending to the southwest through Wisconsin, Minnesota, into Iowa and then westward into Nebraska. To the east of the low, a warm front extended across northern Wisconsin and Lake Michigan, into north-central Michigan. An outflow boundary associated with thunderstorms was depicted just east of the warm front over extreme eastern Michigan into Lake Huron.

The National Center for Atmospheric Research's (NCAR) Research Application Laboratory's (RAL) regional radar mosaic image 2 minutes prior to the accident depicted a defined line of thunderstorms over Lake Michigan and into northeastern Wisconsin in the vicinity of the warm front and another area over eastern Michigan associated with the outflow boundary. There was another large intense-to-extreme area of echoes observed in the vicinity of ORD moving eastward across northern Illinois at approximately 40 knots.

The NWS Storm Prediction Center (SPC) issued a Convective Outlook at 1116 CDT that indicated the potential for thunderstorms and a greater than 30% probability of wind gusts greater than 50 knots, and a 15% probability of hail 1 inch in diameter or larger, and a 2% probability of a tornado in the Chicago area.

ORD's special weather observation at 1429 indicated the wind to be from 230° at 17 knots, gusting to 24 knots, visibility 10 miles in thunderstorm, a few clouds at 5,000 feet agl, scattered clouds at 7,000 feet, ceiling broken at 9,000 feet, and broken at 20,000 feet, temperature 31° Celsius (C), dew point 19° C, altimeter 29.74 inches of mercury (Hg). Remarks: Peak wind from 240° at 27 knots occurred at 1402 CDT, thunderstorm began at 1428 CDT, frequent lightning in cloud-to-cloud and cloud-to-ground to the west. Thunderstorm west moving east, temperature 31.1° C, dew point 19.4° C.

ORD's special weather observation at 1443 indicated the wind to be from 250° at 16 knots gusting to 45 knots. Runway 10L's visual range (RVR) was 700 feet variable to better than 6,000 feet. Weather: thunderstorm, hail, and moderate rain, scattered clouds at 5,000 feet agl. Cumulonimbus and scattered clouds at 7,000 feet, broken ceiling at 9,000 feet, and broken clouds at 20,000 feet. Temperature, 27° C, dew point, 22° C, altimeter 29.76 inches of Hg. Remarks: Peak wind from 270° at 45 knots occurred at 1440 CDT, rain began at 1942, hail began 1943, thunderstorm began 1928, pressure rising rapidly, frequent lightning cloud-to-cloud and cloud-to-ground overhead, thunderstorm overhead moving east, temperature 26.7° C, dew point 21.7° C.