Pilot Debrief

BOEING 777 near Southern Tip of Greenland — 2010-05-25

Final reportDCA10FA064
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Date
2010-05-25
Location
Southern Tip of Greenland, DK
Aircraft
BOEING 777
Registration
N794UA
Category
Airplane
Highest injury
Serious
Fatalities
0

Probable cause

An inadvertent encounter with unforecast turbulence in cruise flight.

NTSB narrative

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.

NTSB coding

View NTSB final report

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