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Cases › WPR11LA149 · Part 121 airline

BOEING 757-232Delta Air Lines

Naches, WA, USA · 2011-02-28·N684DA

0
fatal
1
serious
Serious injury
highest injury
—
damage
Replay the flight data6,601 samples · 11 parameters00:15:00.0 – 02:05:00.0AnalyseThe analystOne timeline · precedents · ask the docket · what the record saysGenerateInvestigation briefFacts, cause, recorder extremes, sequence, sourcesSourceNTSB docket7 documents on data.ntsb.gov

What happened

NTSB summary, verbatim

The flight crew of the scheduled domestic air carrier passenger flight was advised by the air route traffic control center that, due to a pilot report associated with the area of their routing, they should expect light-to-moderate chop during their descent between 20,000 feet and 16,000 feet. The flight crew, therefore, advised the passengers and the flight attendants that the descent would be bumpy and then advised the flight attendants that all descent and before-landing cabin securing activities should be completed about 10 minutes earlier than normal. Before the descent, the flight crew turned on the seatbelt sign and upon reaching 25,000 feet, the flying pilot began reducing the airspeed to that prescribed for turbulence penetration. As the airplane passed through 24,000 feet (4,000 feet higher than the altitude of the turbulence noted in the pilot report), three flight attendants were just finishing their activities, and the airplane suddenly encountered moderate turbulence for about 30 seconds. Due to the sudden movement of the airplane, the one remaining standing passenger and two of the flight attendants were thrown to the floor, one of whom sustained multiple bone fractures in her right foot.

Photographs

6the aircraft, and what the investigators found
The aircraft before the accident
Delta Air Lines B757-232, N684DA, MSN 535 (03 1993), as DL 1735 Atlanta (ATL) - Los Angeles (LAX), Flight time 4 40 (49518005443)
Charles from Port Chester, New York · CC BY 2.0 · Wikimedia Commons
Wreckage and site documentation · 5 photographs from the docket

Photographs are NTSB docket attachments — works of the US government, in the public domain. Captions are the Board’s own.

Probable cause

the Board's determination
The airplane's encounter with moderate turbulence at a higher altitude than the flight crew expected, resulting in an injury to a cabin crewmember.

Occurrence sequence

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

Findings

1 causal · 1 contributing
  • CAUSE
    Environmental issues › Conditions/weather/phenomena › Turbulence › Convective turbulence — Effect on equipment
  • FACTOR
    Environmental issues › Conditions/weather/phenomena › Turbulence › Convective turbulence — Accuracy of related info

Sequence of events

6 timed eventsfrom the FDR factual report · claude-sonnet-5
  1. 2154 MSTDeparturep.1
    Flight departed Salt Lake City, Utah
  2. 2240 PST (approximate)Descentp.1
    Airplane encountered turbulence while in descent about 80 miles southeast of Seattle-Tacoma International Airport
  3. SRN 6148 / 22:20:29 PSTDescentp.3
    As the aircraft was passing through approximately 22,500 feet, there were perturbations noted in the acceleration parameters
  4. 22:20:29 PST (initial part of upset)Descent - Upsetp.3
    The vertical acceleration experienced a change of about 1.7 g's in just over a second and the lateral acceleration had a change of about .3 g's from side to side
  5. approximately one minute durationDescent - Upsetp.3
    The period of disturbance lasted about one minute
  6. ~20 minutes after upsetLandingp.3
    The aircraft continued to descend and landed normally

NTSB analysis

from the final report

The flight crew of the scheduled domestic air carrier passenger flight was advised by the air route traffic control center that, due to a pilot report associated with the area of their routing, they should expect light-to-moderate chop during their descent between 20,000 feet and 16,000 feet. The flight crew, therefore, advised the passengers and the flight attendants that the descent would be bumpy and then advised the flight attendants that all descent and before-landing cabin securing activities should be completed about 10 minutes earlier than normal. Before the descent, the flight crew turned on the seatbelt sign and upon reaching 25,000 feet, the flying pilot began reducing the airspeed to that prescribed for turbulence penetration. As the airplane passed through 24,000 feet (4,000 feet higher than the altitude of the turbulence noted in the pilot report), three flight attendants were just finishing their activities, and the airplane suddenly encountered moderate turbulence for about 30 seconds. Due to the sudden movement of the airplane, the one remaining standing passenger and two of the flight attendants were thrown to the floor, one of whom sustained multiple bone fractures in her right foot.