# NTSB FTW97LA070: British Aerospace BAE 146-200A, N606AW, Denver, CO, December 21, 1996 - Type: NTSB accident investigation - Classification: Accident · Serious injuries · Limited investigation · Final report - Date: December 20, 1996, 17:50 local (Dec 21, 1996, 00:50 UTC) - Place: Denver, CO - Coordinates: 39.849163, -104.699737 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=39.8492&lon=-104.6997&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: Serious injuries - Injuries: 2 serious, 14 uninjured - Status: Completed, report August 29, 1997 - Report: Approved by Office Director - NTSB case key (mKey): 20134 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW97LA070 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/20134/pdf - Page: https://openairdocs.org/ntsb/FTW97LA070 ## Probable cause an inflight encounter with unreported and unanticipated clear air turbulence during landing descent. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - In flight encounter with weather, descent - normal - weather condition - turbulence,clear air (cause) ## Analysis An Air Wisconsin Airline flight, operating as United Express Flight 684, had been cleared to descend from FL190 to 13,000 feet on the Thompson One Arrival into Denver. As the airplane was passing 14,000 feet, it encountered unreported and unanticipated clear air turbulence. Two flight attendants, making their pre-landing check of the cabin, were seriously injured. One flight attendant received fractures to her pelvis, collarbone, and two ribs. The other flight attendant sustained a fractured ankle. ## Factual narrative On December 20, 1996, approximately 1750 mountain standard time, a British Aerospace BAe 146-200A, N606AW, operated by Air Wisconsin Airlines Corporation, d/b/a United Express Flight 684, sustained no damage when it encountered severe turbulence 30 miles northeast of Denver, Colorado. There were no injuries to the two cockpit crew members and 12 passengers, but two flight attendants sustained serious injuries. Visual meteorological conditions prevailed, and an IFR flight plan had been filed for the scheduled domestic passenger flight conducted under Title 14 CFR Part 121. The flight originated at Eagle, Colorado, on December 20, 1996, approximately 1730. The flight had been cleared to descend from FL190 to 13,000 feet on the Thompson One Arrival into Denver. According to the captain's statement, they encountered "one sharp clear air turbulence jolt. Duration was approximately 20 to 30 seconds with moderate turbulence the remainder." The airplane landed without further incident and as it was being taxied to the gate, a passenger contacted the cockpit crew via interphone to advise that both flight attendants had been injured. According to the first officer's statement, the airplane was passing 14,000 feet at 240 knots when speed increased to 270 knots, followed by a severe downdraft. The airplane was "displaced only in pitch, not roll." The turbulence encounter lasted approximately 10 to 15 seconds, followed thereafter by only occasional light turbulence. A passenger then notified the crew via intercom that both flight attendants had been injured. The airplane landed at Denver at 1805 and was met by paramedics who transported the injured flight attendants to a Denver General Hospital. The flight attendant most seriously injured sustained a fractured pelvis, fractured collarbone, and two fractured ribs. In her written statement, she said it had been a smooth flight. She was walking forward to complete the passenger landing check when the airplane hit turbulence and she was thrown off her feet, striking the ceiling. The other flight attendant suffered a fractured ankle. In her written statement, she said the previous flight to Eagle had been routine with no significant weather and very little turbulence. As the airplane began its descent into Denver, the FASTEN SEATBELT sign was illuminated as she and the other flight attendant made their pre-landing checks. She stood to give the passengers instructions over the public address system while the other flight attendant walked through the cabin. She did not recall the turbulence encounter. According to the Denver Air Route Traffic Control Center (ARTCC) and TRACON (terminal radar approach control), no turbulence warnings were issued to United Express flight 684 because they had not received any turbulence reports from other inbound flights. The digital flight data recorder was removed from the airplane and shipped to NTSB's laboratory in Washington, DC, for readout and analysis. According to the laboratory's report, "the aircraft was descending through 14,000 feet when significant excursions in the aircraft's vertical and lateral acceleration occurred. During this time the indicated airspeed increased from 272 to 284 knots. Four seconds after the disruptions began the autopilot disconnected... Immediately thereafter the aircraft's pitch increased about 8 degrees and the vertical acceleration spiked sharply going from a minimum 0f -.75 g's to a maximum of 2.37 g's in about one second. These events were accompanied by a right roll of approximately 6 degrees, yet during this time the aircraft yawed to the left. The airbrake was applied...and the aircraft began to decelerate." ## Aircraft - Registration: [N606AW](https://openairdocs.org/deregistered/N606AW-2011-11-15), registration cancelled 2011-11-15, S/N E2033, built 1985 (OpenAirDocs) - Reported make and model: British Aerospace BAE 146-200A (BAE 146-20) - Registry model: [British Aerospace BAE 146 SERIES 200A](https://openairdocs.org/model/british-aerospace-bae-146-series-200a) (registry code 1500266) (OpenAirDocs) - Registry engine: [Lycoming ALF-502 SER. series](https://openairdocs.org/engine/lycoming-alf-502-ser-series) (registry code 41580, turbo-jet) (OpenAirDocs) - Category: Airplane - Serial number: E2033 - Airframe hours: 21438 - Engines: Lycoming ALF-502-R5 6700 lbs thrust turbo fan - Damage: No damage - Flight: Part 121 - Operator: Air Wisconsin Airlines, doing business as United Express - Registered owner: Wilmington Trust Company - Airworthiness certificate: Standard, Transport - Last inspection: Continuous airworthiness, December 17, 1996, 31 hours before - Departed: EGE, EAGLE, CO - Destination: DEN, CO - Flight plan: IFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 47; commercial, airline transport; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 1, valid medical--w/ waivers/lim; seat: left; flight hours: 7,155 total, 2,171 in this make and model, 148 in the last 90 days, 64 in the last 30 days, 17 in the last 24 hours ## Weather - Conditions: Visual (VMC), Night/bright - Wind: 20° at 3 knots - Visibility: 10 statute miles - Lowest ceiling: 16,000 ft broken - Temperature: 37 °F, dew point 19 °F - Altimeter: 29.00 inHg - Observed at: DEN, 30 nm away ## 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 19961220047279A](https://openairdocs.org/incident/19961220047279A), Dec 20, 1996: Denver, CO, No damage. (-16) Two flight attendants injured due to in-flight turbulence. ## Other investigations on N606AW (1) 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. - [NTSB CHI00IA037](https://openairdocs.org/ntsb/CHI00IA037), Dec 1, 1999: British Aerospace BAE 146-200A (N606AW), Chicago, IL, incident, minor damage. Probable cause: An undetermined failure in the hydraulic system, which resulted in the airplane's entire braking system becoming temporarily inoperative. A factor associated with the incident was the airport… 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.