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Cases › DCA14LA060 · Part 121 airline

BOEING 737Continental Airlines

Kaycee, WY, USA · 2014-02-17·N23708

0
fatal
2
serious
Serious injury
highest injury
—
damage
Replay the flight data328,573 samples · 29 parameters12:08:00.0 – 13:23:00.9AnalyseThe analystOne timeline · precedents · ask the docket · what the record saysGenerateInvestigation briefFacts, cause, recorder extremes, sequence, sourcesSourceNTSB docket12 documents on data.ntsb.gov

What happened

NTSB summary, verbatim

The flight departed normally and climbed to its cruising altitude where it encountered light turbulence. The flight crew descended to a lower altitude twice in an effort to find a smooth ride. The flight encountered an area of severe mountain wave turbulence when the flight was cruising at flight level (FL) 340 in smooth air with the seat belt sign off seriously injuring two flight attendants. According to the NTSB weather study, an Airman's Meteorological Information (AIRMET) for moderate turbulence for altitudes between FL270 and FL390 was issued at 0745 MST for a region that included the accident location. The flight dispatch release for the accident aircraft, which included weather information, included a Flight Planning Guidance product from WSI that advised of light/occasional moderate mountain wave activity between FL310 and FL390 close to where the accident occurred.

Probable cause

the Board's determination
an encounter with severe mountain wave turbulence during cruise flight.

Occurrence sequence

1 stepsNTSB coding · CICTT taxonomy
  1. 1 · Enroute
    Turbulence encounter
    defining event

Findings

1 causal · 0 contributing
  • CAUSE
    Environmental issues › Conditions/weather/phenomena › Turbulence › Convective turbulence — Effect on personnel

Sequence of events

7 timed eventsfrom the FDR factual report · claude-fable-5-1 (in-session)
  1. 12:08:00 MSTtakeoffp.2
    Start of plotted flight data (figures 1 and 2 cover the entire flight from 12:08:00 MST to 13:23:00 MST)
  2. 12:54:37 MSTcruisep.3
    About 44 minutes after takeoff, vertical acceleration variations began, ranging between 2.05 g and -1.23 g before settling to 1 g at 12:55:22; pressure altitude started at about 34,000 ft and decreased to about 33,000 ft
  3. 12:54:50 MSTcruisep.3
    Autopilot command-B (AP Cmd-B) transitioned from Selected to Not Selected
  4. 12:55:22 MSTcruisep.3
    Vertical acceleration variations ended, settling to 1 g; position at the -1.23 g point was approximately 43.7200193 N, 106.962891 W
  5. 12:57:58 MSTcruisep.3
    2 minutes 36 seconds after vertical acceleration settled, AP Cmd-B transitioned back to Selected and pressure altitude decreased to about 32,000 ft
  6. 13:01:29 MSTdescentp.3
    Aircraft descended for landing
  7. about 13:21 MSTlandingp.3
    Aircraft landed, approximately 20 minutes after beginning the descent

NTSB analysis

from the final report

The flight departed normally and climbed to its cruising altitude where it encountered light turbulence. The flight crew descended to a lower altitude twice in an effort to find a smooth ride. The flight encountered an area of severe mountain wave turbulence when the flight was cruising at flight level (FL) 340 in smooth air with the seat belt sign off seriously injuring two flight attendants. According to the NTSB weather study, an Airman's Meteorological Information (AIRMET) for moderate turbulence for altitudes between FL270 and FL390 was issued at 0745 MST for a region that included the accident location. The flight dispatch release for the accident aircraft, which included weather information, included a Flight Planning Guidance product from WSI that advised of light/occasional moderate mountain wave activity between FL310 and FL390 close to where the accident occurred.