Accident Boeing 777-222ER N794UA,
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Date:Tuesday 25 May 2010
Type:Silhouette image of generic B772 model; specific model in this crash may look slightly different    
Boeing 777-222ER
Owner/operator:United Airlines
Registration: N794UA
MSN: 26953/105
Year of manufacture:1997
Fatalities:Fatalities: 0 / Occupants: 211
Aircraft damage: None
Location:over Atlantic Ocean -   Canada
Phase: En route
Nature:Passenger - Scheduled
Departure airport:London Heathrow Airport (LHR/EGLL)
Destination airport:Los Angeles, CA (LAX)
Investigating agency: NTSB
Confidence Rating: Accident investigation report completed and information captured
The flight encountered clear air turbulence near the southern tip of Greenland. A review of the weather briefing provided to the accident flight crew by company Flight Dispatch contained relevant SIGMETs along the proposed route of flight. The package was not found to be missing any pertinent published information that could have alerted the flight crew to an enroute encounter with turbulence over Greenland.

Analysis of the calculated winds indicated the airplane encountered a downdraft on the order of 13 feet/sec followed sharply by an updraft of approximately 24 feet/sec. Simulation analysis of the upset
confirmed that the airplane reacted as expected to the calculated wind profile and the recorded control inputs. Based on the simulation study that was performed, the recorded elevator input from the autopilot during the disturbance reduced the magnitude
of the upset.

Analysis of the surrounding atmosphere and GOES-3 satellite photographs indicated the presence of icecap wave instability along the airplane's route of flight that was capable of producing rapidly changing vertical winds on the order of 20 feet per second, which resulted in conditions conducive to severe turbulence.
Probable Cause: An inadvertent encounter with unforecast turbulence in cruise flight.




Revision history:

25-May-2010 23:50 tatoberry Added
26-May-2010 00:04 harro Updated [Aircraft type, Cn, Location, Departure airport, Destination airport, Source, Embed code, Damage, Narrative]
02-Sep-2010 14:39 Anon. Updated [Nature, Embed code]
21-Dec-2016 19:25 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
26-Nov-2017 17:13 ASN Update Bot Updated [Operator, Other fatalities, Departure airport, Destination airport, Source, Narrative]

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