# NTSB DCA23LA305: Boeing 737-924ER, N28457, Chicago, IL, June 1, 2023 - Type: NTSB accident investigation - Classification: Accident · Serious injuries · Class 4 · Limited · Final report - Date: June 1, 2023, 17:06 local (22:06 UTC) - Place: Chicago, IL - Coordinates: 42.6315, -88.2718 - Nearby events: https://openairdocs.org/map.md?lat=42.6315&lon=-88.2718&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-descent: Turbulence encounter](https://openairdocs.org/ntsb-events/360) - Highest injury: Serious injuries - Injuries: 1 serious, 185 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 4 - Basic report with no Prelim publish - NTSB office: Major Investigations Division - Parties: FAA - NTSB case key (mKey): 192293 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DCA23LA305 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/192293/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=192293 - Page: https://openairdocs.org/ntsb/DCA23LA305 ## Probable cause An encounter with convectively-induced turbulence (CIT). ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Convective weather](https://openairdocs.org/ntsb-findings/03033000): Environmental issues › Conditions/weather/phenomena · Effect on personnel; cases with it: [Boeing 737-924ER, 1 case](https://openairdocs.org/ntsb-findings/03033000/cases.md?model=13848A3), [All aircraft, 17 cases](https://openairdocs.org/ntsb-findings/03033000/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute-descent: Turbulence encounter](https://openairdocs.org/ntsb-events/360) (defining event); cases with it: [Boeing 737-924ER, 4 cases](https://openairdocs.org/ntsb-events/360/sequence.md?model=13848A3), [All aircraft, 423 cases](https://openairdocs.org/ntsb-events/360/sequence.md) ## Analysis A flight attendant was seriously injured when United Airlines flight 1734 encountered convectively-induced turbulence during the descent into the Chicago O'Hare International Airport (ORD), Chicago, Illinois. Flight 1734 originated from the San Francisco International Airport (SFO) and the captain was the pilot monitoring and the first officer was the pilot flying. The flight crewmembers reported that they were not aware of any adverse reports of turbulence from either air traffic control (ATC), or other aircraft and they found the route along the arrival path to be generally smooth. Their weather radar was on and showed some cells located to the west of ORD, but none were along either their arrival route, the airport itself, or the area east of ORD where they conducted their approach to landing. When they first checked in with the Chicago approach controller, they were assigned runway 27R. However, they preferred a longer runway due to their landing weight and were therefore assigned runway 28C which they had to load into the flight management computer and re-brief. The captain indicated that the seat belt sign had been turned on early in the descent during the “arrival” passenger announcement. About 13,000 ft, the captain gave the cabin crew the “double chime” indicating that they should prepare the cabin for landing and then take their seats. The flight crewmembers reported that as the aircraft was descending through an isolated overcast layer, they observed a small cloud buildup with the top of the buildup slightly above their altitude. They contacted ATC and requested and were approved to make a left turn to avoid the cloud build-up. Although they attempted to avoid the cloud, the aircraft penetrated the left outermost area of the cloud buildup at an altitude of approximately 12,100 ft. The flight crewmembers indicated that as they went through this area, they experienced about 5 seconds of light to borderline moderate turbulence. As soon as they exited the area, the air was once again smooth. Shortly after the encounter, the flight crewmembers received a call from the cabin crew informing them that one of the flight attendants had fallen in the rear galley and had injured her foot. According to the cabin crew, shortly after they heard the double chime, there was a big bump of turbulence, and a flight attendant lost her balance, twisted her ankle, and hit her back on the corner of her jump seat. A physician who was onboard the airplane assisted her and helped move her to a passenger seat for the remainder of the flight. Emergency medical personnel met the airplane at the gate and a post-flight medical evaluation revealed that the flight attendant had a fracture injury to her metatarsal bone in the left foot. Based on a review of WSR-88Dweather radar (KMKX), satellite (GOES-16), and upper air model (HRRR) data, the turbulence encounter appeared generally coincident in time and location with a convective updraft that reached heights above12,100 ft. ## Aircraft - Registration: [N28457](https://openairdocs.org/aircraft/N28457), registered now, S/N 41744, built 2012 (OpenAirDocs) - Reported make and model: BOEING 737-924ER - Registry model: [Boeing 737-924ER](https://openairdocs.org/model/boeing-737-924er) (registry code 13848A3) (OpenAirDocs) - Registry engine: [CFM International CFM56-7B26E series](https://openairdocs.org/engine/cfm-international-cfm56-7b26e-series) (registry code 13099, turbo-fan) (OpenAirDocs) - Category: Airplane - Serial number: 41744 - Year built: 2012 - Engines: CFM INTL CFM56-7B27 273000 lbs thrust turbo fan; CFM INTL CFM56-7B27 27300 lbs thrust turbo fan - Damage: No damage - Flight: Part 121 - Operator: United Airlines Inc - Registered owner: United Airlines Inc - Airworthiness certificate: Standard, Transport - Departed: KSFO, San Francisco, CA - Destination: KORD, Chicago, IL - Flight plan: IFR - Equipment: Electronic primary flight display, Heads up display, Stall warning system, ADS-B, Data recorder, Electronic flight bag or handheld device, Electronic multifunction display ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 55; injuries: none; airline transport; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 1, with waivers/limitations; last flight review May 23, 2023; seat: left; restraint: 4-point; flight hours: 22,950 total, 17,558 in this make and model, 13,445 as pilot in command, 142 in the last 90 days, 12 in the last 30 days, 0 in the last 24 hours - Pilot; age 54; injuries: none; airline transport; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 1, with waivers/limitations; last flight review February 14, 2023; seat: right; restraint: 4-point; flight hours: 15,600 total, 2,800 in this make and model, 10,300 as pilot in command, 200 in the last 90 days, 36 in the last 30 days, 0 in the last 24 hours ## Weather - Conditions: Visual (VMC), Not reported - Wind: 200° at 7 knots - Visibility: 10 statute miles - Lowest ceiling: 6,000 ft broken - Temperature: 79 °F, dew point 61 °F - Altimeter: 30.06 inHg - Icing: Unknown - Turbulence: Light - Observed at: KBUU, 3.85 nm away ## Docket (4 files) The files NTSB released with the investigation on October 16, 2023, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=192293. 23.7 MB in all. - Flight crew statements (item 1, PDF, 2 pages, 92 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15738083&FileExtension=pdf&FileName=UAL1734%20CA%20and%20FO%20Statements-Rel.pdf - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 2, PDF, 11 pages, 2.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16108080&FileExtension=pdf&FileName=6120_Redacted-Rel.pdf - ADS-B data (item 3, XLSX, 21.5 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16108322&FileExtension=xlsx&FileName=ADS-B%20-%20UAL1734-Rel.xlsx - Cabin crew statements (item 4, PDF, 2 pages, 80 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16191723&FileExtension=pdf&FileName=Statements%20-%20Flight%20Attendants_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.