Accident Boeing 777-222ER N209UA,
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Date:Wednesday 18 November 2009
Time:20:30 LT
Type:Silhouette image of generic B772 model; specific model in this crash may look slightly different    
Boeing 777-222ER
Owner/operator:United Airlines
Registration: N209UA
MSN: 30215/259
Year of manufacture:1999
Total airframe hrs:41788 hours
Engine model:Pratt & Whitney PW 4090
Fatalities:Fatalities: 0 / Occupants: 200
Aircraft damage: None
Category:Accident
Location:New Market, West Virginia -   United States of America
Phase: En route
Nature:Passenger - Scheduled
Departure airport:Chicago-O'Hare International Airport, IL (ORD/KORD)
Destination airport:Washington-Dulles International Airport, DC (IAD/KIAD)
Investigating agency: NTSB
Confidence Rating: Accident investigation report completed and information captured
Narrative:
Prior to and after the turbulence encounter the captain reported smooth air while level at FL310. There were no reported sigmets, airmets, or pilot reports issued, nor were there 'watch boxes” that warned of adverse weather. The onboard weather radar was functioning when suddenly the airplane went through a cloud at Mach 0.84 and encountered moderate turbulence for about 10 to 15 seconds. He said that there was an overspeed warning alarm and he immediately took over manual control of the airplane maintaining control, and activated the seat belt warning sign which had previously been off, since the flight had been smooth. The first officer statement was consistent with the captain's and in addition he reported seeing 'considerable St. Elmo's Fire” throughout the duration of the turbulence.

The aircraft's flight data recorder indicated that while the aircraft was level at FL310, the vertical acceleration changed from 1.25 g's to -0.5 g's in less than one second and then abruptly reached 2.0 g's within a few seconds before reducing to minor oscillations that were between 1.25 g's and 0.75 g's which lasted for about 15 seconds. According to the FDR data, the turbulence lasted about 20 seconds.

The NTSB conducted a meteorological study to assess weather conditions in the area where the flight encountered turbulence, and the National Weather Service's Radar Summary for 1918 EST depicted an extensive area of rain showers over the region with a few radar echo tops between 31,000 feet and 48,000 feet. In addition, the regional radar composite imagery showed that between 1910 and 1940 EST there was a small area of reflectivity between 5 and 25 decibels in the area of the turbulence encounter.

Probable Cause: The flight crew's inadvertent encounter with a small area of cumulous clouds at night that resulted in moderate to severe convectively induced turbulence.

Accident investigation:
cover
  
Investigating agency: NTSB
Report number: DCA10FA012
Status: Investigation completed
Duration: 2 years 1 month
Download report: Final report

Sources:

NTSB DCA10FA012

History of this aircraft

Other occurrences involving this aircraft
18 August 2023 N209UA United Airlines 0 over Northern Atlantic Ocean non
Turbulence

Location

Revision history:

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