# NTSB CHI99LA184: Boeing 777-222, N781UA, Madison, WI, June 12, 1999 - Type: NTSB accident investigation - Classification: Accident · Serious injuries · Limited investigation · Final report - Date: June 11, 1999, 21:18 local (Jun 12, 1999, 02:18 UTC) - Place: Madison, WI - Coordinates: 43.056832, -89.404014 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=43.0568&lon=-89.4040&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: Serious injuries - Injuries: 1 serious, 8 minor, 287 uninjured - Status: Completed, report June 22, 2000 - Report: Approved by Office Director - NTSB case key (mKey): 46549 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI99LA184 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/46549/pdf - Page: https://openairdocs.org/ntsb/CHI99LA184 ## Probable cause the pilot-in-command's inadequate evaluation of the weather conditions. Factors associated with the accident were the turbulence encountered and the seat belt sign was not illuminated. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Altitude deviation,uncontrolled, descent - normal - weather condition - turbulence (contributing factor) - weather evaluation - inadequate, pilot in command (cause) - seat belt sign - not used, pilot in command (contributing factor) ## Analysis While en route from Minneapolis to Chicago the flight encountered turbulence at 19,680 feet msl while in a descent. Four passengers and four flight attendants received minor injuries. One passenger received a broken ankle. The flight had diverted to Minneapolis due to thunderstorm activity in the Chicago area. The captain reported the flight was smooth up until the unexpected turbulence was encountered. The seat belt sign was not on at the time of the encounter. The flight crew received a Weather Briefing Message (WBM) prior to departing Minneapolis, which contained convective sigmets for Wisconsin, Illinois, and Indiana. The accident took place ahead of a stationary front which extended northeast-southwest through central Wisconsin and Iowa which had been creating shower and thunderstorm activity throughout afternoon and evening on the day of the accident. A review of the data from the Quick Access Recorder revealed the flight experienced a change in G-loading from .0843 g's to 1.9375 g's over a 2-second time period while at an altitude of 19,680 feet msl. ## Factual narrative On June 11, 1999, at 2118 central daylight time (cdt), a Boeing 777-222, N781UA, operated by United Airlines as flight 256 encountered turbulence during a descent near Madison, Wisconsin. Four passengers received minor injuries and one passenger was seriously injured. Four flight attendants received minor injuries. Both cockpit crewmembers, 6 flight attendants, and 279 passengers were not injured. The airplane was not damaged. The 14 CFR Part 121 passenger flight was operating in visual meteorological conditions on an IFR flight plan. The flight was originally scheduled from Denver, Colorado, to Chicago, Illinois; however, it diverted to Minneapolis, Minnesota due to thunderstorms in the Chicago area. The flight departed from Minneapolis, Minnesota, at 2048 cdt. The flight continued on to Chicago after the turbulence encounter where it landed uneventfully, at the Chicago O'Hare International Airport, at 2149 cdt. The captain reported the flight was smooth up until the unexpected turbulence was encountered while they were descending through 18,000 feet msl. He reported the moderate turbulence lasted 20 to 30 seconds after which the remainder of the flight was smooth. The seat belt sign was not on at the time of the turbulence encounter. The captain reported the radar was on and it was showing no indication of cells or turbulence along the route. He reported there was a rain shower at their 2 o'clock position, 30 miles away. The first officer reported that moderate turbulence was encountered during the descent at an altitude of about 17,000 feet msl. He reported, "It consisted of a 2-3 second period of negative "g" followed by a 2-3 second positive "g" deviation, then a two to five minute period of light to moderate slight deviations from our flight path." He reported there was nothing on the radar in their area, but convective activity was displayed beyond the Chicago area. The flight attendants reported that all the passengers that were injured were out of their seats and in the back of the airplane when the turbulence was encountered. The most serious injury was a passenger who suffered a broken ankle. According to United Airlines, the flight crew received a Weather Briefing Message (WBM) prior to departing Minneapolis, which contained convective sigmets for Wisconsin, Illinois, and Indiana. The accident took place ahead of a stationary front which extended northeast-southwest through central Wisconsin and Iowa which had been creating shower and thunderstorm activity throughout afternoon and evening on the day of the accident. A review of recorded aircraft data revealed the flight experienced a change in G-loading from .0843 g's to 1.9375 g's over a 2-second time period while at an altitude of 19,680 feet msl. ## Aircraft - Registration: [N781UA](https://openairdocs.org/aircraft/N781UA), registered now, S/N 26945, built 1996 (OpenAirDocs) - Reported make and model: Boeing 777-222 - Registry model: [Boeing 777-222](https://openairdocs.org/model/boeing-777-222) (registry code 1385219) (OpenAirDocs) - Registry engine: [Pratt & Whitney PW4000 series](https://openairdocs.org/engine/pratt-whitney-pw4000-series) (registry code 52119, turbo-fan) (OpenAirDocs) - Category: Airplane - Serial number: 26945 - Airframe hours: 11389 - Engines: P&W PW4077 77000 lbs thrust turbo fan - Damage: No damage - Flight: Part 121 - Registered owner: United Air Lines, Inc. - Airworthiness certificate: Standard, Transport - Last inspection: Continuous airworthiness, May 11, 1999, 390 hours before - Departed: MSP, MINNEAPOLIS, MN - Destination: ORD, CHICAGO, IL - Flight plan: IFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 56; airline transport, flight engineer, flight instructor; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 1, valid medical--no waivers/lim.; seat: left; flight hours: 23,000 total, 75 in this make and model, 104 in the last 90 days, 64 in the last 30 days, 13 in the last 24 hours ## Weather - Conditions: Visual (VMC), Night/dark - Wind: 180° at 15 knots - Visibility: 10 statute miles - Lowest ceiling: 4,600 ft broken - Temperature: 77 °F, dew point 64 °F - Altimeter: 30.00 inHg - Observed at: MSN ## 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 19990611046209A](https://openairdocs.org/incident/19990611046209A), Jun 11, 1999: Boeing 777222, Madison, WI, No damage. (-23) United flight 256 encountered unexpected clear air turbulence while descending through FL180. The turbulence lasted 20 to 30 seconds; the remainder of… 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.