United Airlines Boeing 777 200B accident
Boeing 777 200B · Accident: turbulence encounter en route
From London Heathrow Airport (LHR) to Los Angeles International Airport (LAX)
Event
- NTSB case
- DCA10FA064
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Accident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 0 · all aircraft and ground
- Ground fatalities
- Unknown
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- Airline
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Visual Meteorological Cond
Boeing 777 200B
- Aircraft type
- Boeing 777
- Category
- Airplane
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N794UA
- Operator
- United Airlines
- Onboard fatalities
- Unknown
- Route
- From London Heathrow Airport (LHR), LondonTo Los Angeles International Airport (LAX), Los Angeles, CA
- Aircraft age
- Not recorded
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 121: Air Carrier
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- En route · cruise
- Defining eventThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Turbulence encounter
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- None
Cause areas
- Environmental issues › Conditions/weather/phenomena
Not plotted · Location withheld: coordinates are missing, conflicting, invalid, or have no accepted acquisition method. No substitute location has been invented.
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.
Probable cause
An inadvertent encounter with unforecast turbulence in cruise flight.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record DCA10FA064
- Event ID
- 20100525X31845
- Case number
- DCA10FA064
- Dataset
- full-current
- Source SHA-256
- 5cf380f0061817c0331a6b2d8cc7e0ee3a79bea469a1001dc5c10e56f35f5ab3
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: investigation status, damage. Values present in the bulk record are kept.
- The date is the local date, which is the same as the UTC date the NTSB stores.
- API snapshot SHA-256: 693b9798071a6f99cebe4f994b0e1d5ac96cf3dad4ab3d0fef4edbc5b365156a; retrieved 2026-09-15T14:13:17.587Z.