# NTSB DCA17LA183: Bombardier CL 600 2C10, N745SK, McKellar, TN, August 22, 2017 - Type: NTSB accident investigation - Classification: Accident · Serious injuries · Class 3 · Limited · Final report - Date: August 22, 2017, 17:21 local (22:21 UTC) - Place: McKellar, TN - Coordinates: 35.599998, -88.915557 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=35.6000&lon=-88.9156&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-cruise: Turbulence encounter](https://openairdocs.org/ntsb-events/360) - Highest injury: Serious injuries - Injuries: 2 serious, 9 minor, 63 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Major Investigations Division - NTSB case key (mKey): 95885 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DCA17LA183 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/95885/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=95885 - Page: https://openairdocs.org/ntsb/DCA17LA183 ## Probable cause An encounter with convective turbulence while maneuvering to avoid conflicting traffic. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Turbulence: convective turbulence](https://openairdocs.org/ntsb-findings/03032020): Environmental issues › Conditions/weather/phenomena · Effect on personnel (probable cause); cases with it: [Bombardier CL-600-2C10, 1 case](https://openairdocs.org/ntsb-findings/03032020/cases.md?model=1390015), [All aircraft, 145 cases](https://openairdocs.org/ntsb-findings/03032020/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute-cruise: Collision avoidance alert](https://openairdocs.org/ntsb-events/420); cases with it: [Bombardier CL-600-2C10, 1 case](https://openairdocs.org/ntsb-events/420/sequence.md?model=1390015), [All aircraft, 11 cases](https://openairdocs.org/ntsb-events/420/sequence.md) - [Enroute-cruise: Abrupt maneuver](https://openairdocs.org/ntsb-events/270); cases with it: [Bombardier CL-600-2C10, 1 case](https://openairdocs.org/ntsb-events/270/sequence.md?model=1390015), [All aircraft, 346 cases](https://openairdocs.org/ntsb-events/270/sequence.md) - [Enroute-cruise: Turbulence encounter](https://openairdocs.org/ntsb-events/360) (defining event); cases with it: [Bombardier CL-600-2C10, 1 case](https://openairdocs.org/ntsb-events/360/sequence.md?model=1390015), [All aircraft, 423 cases](https://openairdocs.org/ntsb-events/360/sequence.md) ## Analysis While in cruise flight around 36,000 ft, the flight crew of the scheduled domestic passenger flight was instructed by air traffic control to turn for traffic separation. The crew reported that, after completing the turn, the airplane entered a cloud and encountered severe turbulence. The seat belt sign was not activated at the time of the encounter, and of the 74 passengers and crew members aboard, one passenger received serious injuries and two flight attendants and eight passengers received minor injuries. The airplane was not damaged. According to flight data recorder information, during the encounter, vertical acceleration ranged from -0.8g to 1.89g, the airplane lost about 200 ft altitude in 2 seconds, and the airspeed varied by about 15 knots. The airplane entered an 11.6° nose-down pitch attitude and rolled 26 degrees to the left. The crew reported that the flight until the encounter had been smooth. They reported that they could see the cloud build-up as they were approaching it from about 80 to 100 miles away, but that their radar did not indicate that they were going to encounter convective weather. The company's flight operations manual stated that, before entering an area of thunderstorms, pilots were required to ensure that all personnel were seated and safety belts were fastened. ## Factual narrative On August 22, 2017, about 1721 central daylight time, a Bombardier CRJ700, N745SK, operated as SkyWest Airlines, d.b.a American Eagle flight 3167, encountered turbulence in cruise flight and diverted to Lambert-St. Louis International Airport (KSTL), St. Louis, Missouri. Of the 74 passengers and crew members aboard, one passenger received serious injuries; two flight attendants and eight passengers received minor injuries. The airplane was not damaged. The airplane was operated as a Title 14 Code of Federal Regulations Part 121 regularly scheduled domestic passenger flight. The crew reported that they were in visual meteorological conditions with no turbulence, and that they could see the convective weather as they were approaching it from about 80-100 miles away. As they approached the area, the controller cleared the flight to deviate around the weather to the left, and shortly thereafter, the controller issued instructions to turn 10° right for traffic. The flight crew initially declined the turn due to their concern that the flight would enter adverse weather. The controller then repeated the instructions to turn right, and the crew subsequently complied. After completing the turn, the airplane flew into the tops of clouds and encountered severe turbulence at 36,000 feet. According to the crew, the encounter lasted several seconds; the seat belt sign was not activated. At the time, the flight attendants were conducting beverage service, and the flight attendants and galley cart struck the overhead cabin. According to the flight crew, the encounter resulted in a 200-foot altitude loss and momentary activation of the stall warning system stick shaker. The captain reported that company guidance stated that the seat belt sign be turned on anytime turbulence could be expected, and added that his decision to keep the seat belt sign off was based on the flight conditions leading up to the event, since there was no turbulence, and "there was nothing on the radar indicating what they were going to encounter" convective weather. According to flight data recorder (FDR) information, the turbulence event occurred as the airplane was passing through about 35,750 ft. During the encounter, vertical acceleration ranged from -0.8g to 1.89g, the airplane lost 200 ft altitude in 2 seconds, and the airspeed varied by about 15 knots. The airplane's heading changed 5 degrees to the left in one second, and the airplane entered a pitch attitude of 11.6° nose-down, and rolled 26° to the left. SkyWest Airlines Flight Operations Manual (FOM), Section F, "General Turbulence Procedures," specified that before entering an area of thunderstorms pilots were required to ensure that all personnel are seated and safety belts were fastened. Chapter 07 of the manual, "Adverse Weather," stated in part: When turbulence is expected/forecast, the PIC [pilot-in-command] is responsible to ensure crew and passengers are adequately briefed and prepared. Briefings must include turbulenceconsiderations, location, intensity, and possible duration. When flight into forecast turbulence is unavoidable or an unforecast encounter occurs, timely notification to the FAs [flight attendants] and passengers is crucial. Notification is given as far in advance as possible using the interphone. Do not rely on the seat belt sign alone. When asked about their company guidance for thunderstorm avoidance, the captain stated that their FOM specified 20 miles away and that the preferred distance was 10 miles. The FOM stated that prior to entering an area of thunderstorms, pilots were required to "monitor radar constantly and alter flight path to miss intense build-ups by 10 miles or more (20-mile clearance is best when possible, particularly at altitudes above the freezing level)." When asked about the radar settings before the turbulence encounter, the captain stated that, "the gain would have been in auto, and with a pitch of 1 degree." He said that he adjusted the tilt as they approached the weather to give them the best picture to avoid ground clutter, and did not change the tilt once closer to the weather. Radar techniques were included in the SkyWest Airlines FOM and stated in part: - Use preset gain or, when this feature is not available, a constant low gain setting. - Take particular care to avoid storms with hooked fingers, figure six echoes, sharp rainfall gradients, and rapidly changing shapes. - Never fly under the overhang of a thunderstorm. - A 40-mile range is good, but frequent check of longer ranges must be made to avoid flying into a blind alley. ## Aircraft - Registration: [N745SK](https://openairdocs.org/aircraft/N745SK), registered now, S/N 10201, built 2005 (OpenAirDocs) - Reported make and model: BOMBARDIER INC CL 600 2C10 (700C) - Registry model: [Bombardier CL-600-2C10](https://openairdocs.org/model/bombardier-cl-600-2c10) (registry code 1390015) (OpenAirDocs) - Registry engine: [GE CF34 series](https://openairdocs.org/engine/ge-cf34-series) (registry code 30015, turbo-fan) (OpenAirDocs) - Category: Airplane - Serial number: 10201 - Year built: 2005 - Airframe hours: 36393 - Engines: GE CF34 SERIES 9140 horsepower turbo fan; GE CF34 SERIES 9140 horsepower turbo fan - Damage: No damage - Flight: Part 121 - Operator: Skywest Airlines, doing business as American Eagle - Registered owner: Wells Fargo Bank Northwest Na Trustee - Airworthiness certificate: Standard, Transport - Last inspection: Continuous airworthiness, August 12, 2017 - Departed: KATL, Atlanta, GA - Destination: KORD, Chicago, IL - Flight plan: IFR - Equipment: Electronic multifunction display, Data recorder, Auto-pilot, Electronic primary flight display ## Flight crew As NTSB recorded them. NTSB leaves out names. - Co-pilot; age 26; injuries: none; airline transport; airplane ratings: multi-engine land; instrument ratings: airplane; medical: class 1, unknown; last flight review March 7, 2017; seat: right; flight hours: 2,541 total, 1,033 in this make and model, 199 in the last 90 days, 4 in the last 24 hours - Pilot; age 34; injuries: none; airline transport; airplane ratings: multi-engine land; instrument ratings: airplane; medical: class 1, unknown; seat: left; flight hours: 8,121 total, 4,642 in this make and model, 265 in the last 90 days, 4 in the last 24 hours ## Weather - Conditions: Instrument (IMC), Day - Altimeter: 29.92 inHg - Icing: Unknown - Turbulence: Unknown ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 20170822011249A](https://openairdocs.org/incident/20170822011249A), Aug 22, 2017: Bombardier Inc CL-600-2C10, Dyersburg, TN, No damage. The crew was issued a heading for traffic. On that heading, the aircraft flew into weather and encountered severe turbulence. The aircraft diverted due to… ## Docket (8 files) The files NTSB released with the investigation on July 13, 2021, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=95885. 18.5 MB in all. - Operations specialist report (item 1, PDF, 14 pages, 1 photo, 327 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=6282461&FileExtension=pdf&FileName=DCA17LA183%20Ops%20Specialist%20Report%20(FINAL)-Rel.pdf - Operations attachment 1- interview summaries (item 2, PDF, 10 pages, 399 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=6282744&FileExtension=pdf&FileName=Attachment%201-%20Interview%20Summaries-Rel.pdf - Operations attachment 2 - flight release (item 3, PDF, 29 pages, 485 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=6282587&FileExtension=pdf&FileName=Attachment%202%20-%20Flight%20Release_Redacted-Rel.pdf - Operations attachment 3 - crew statements (item 4, PDF, 3 pages, 375 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=6282753&FileExtension=pdf&FileName=Attachment%203%20-%20Crew%20Statements-Rel.pdf - Operations attachment 4 - FAA advisory circular 120-88 (item 5, PDF, 21 pages, 313 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=6282284&FileExtension=pdf&FileName=Attachment%204%20-%20FAA%20Advisory%20Circular%20120-88-Rel.pdf - Flight data recorder specialist's factual report (item 6, PDF, 12 pages, 2.5 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=6199405&FileExtension=pdf&FileName=Flight%20Data%20Recorder%20Specialist%27s%20Factual%20Report-Rel.pdf - Flight data recorder specialist's factual report attachment 1 (item 7, CSV, 12.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=6199833&FileExtension=csv&FileName=Flight%20Data%20Recorder%20Specialist%27s%20Factual%20Report%20Attachment%201-Rel.csv - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 8, PDF, 11 pages, 2.0 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=12147859&FileExtension=pdf&FileName=DCA17LA183-NTSB%206120%20form%203167%20turbulence%20(updated)_Redacted-Rel.pdf From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.