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Cases › WPR10LA134 · Part 121 airline

BOEING 737-7H4SOUTHWEST AIRLINES CO

Santa Clarita, CA, USA · 2010-02-13·N221WN

0
fatal
1
serious
Serious injury
highest injury
—
damage
Replay the flight data24,840 samples · 41 parameters20:44:30.0 – 20:53:29.9AnalyseThe analystOne timeline · precedents · ask the docket · what the record saysGenerateInvestigation briefFacts, cause, recorder extremes, sequence, sourcesSourceNTSB docket8 documents on data.ntsb.gov

What happened

NTSB summary, verbatim

During descent to landing, the flight crew inadvertently turned about 27 degrees off their air traffic controller-assigned heading. When advised by the controller to check the airplane’s heading, the flight crew noted the heading discrepancy and immediately initiated a turn back to the assigned heading. During the turn, the flight crew received a traffic alert and collision avoidance system resolution advisory (RA). The captain responded to the RA by initiating an estimated 1,500- to 2,000-foot-per-minute rate of descent followed by an approximate 2,000-foot-per-minute climb. During the RA response maneuvers, three flight attendants were standing in the aft galley, one of whom was seriously injured.

Photographs

1the aircraft, and what the investigators found
The aircraft before the accident
Boeing 737-7H4(w) ‘N221WN’ Southwest (28433586093)
Alan Wilson from Stilton, Peterborough, Cambs, UK · CC BY-SA 2.0 · Wikimedia Commons

Probable cause

the Board's determination
The pilot’s abrupt airplane pitch change maneuver. Contributing to the accident was the flight crew’s failure to maintain the heading specified by the air traffic controller, which would have avoided the near collision course with an unidentified airplane that triggered the traffic alert and collision avoidance system resolution advisory.

Occurrence sequence

2 stepsNTSB coding · CICTT taxonomy
  1. 1 · Approach-IFR initial approach
    Collision avoidance alert
  2. 2 · Approach-IFR initial approach
    Abrupt maneuver
    defining event

Findings

3 causal · 0 contributing
  • CAUSE
    Aircraft › Aircraft oper/perf/capability › Performance/control parameters › Pitch control — Incorrect use/operation
  • CAUSE
    Personnel issues › Task performance › Use of equip/info › Aircraft control — Pilot
  • CAUSE
    Environmental issues › Operating environment › Air traffic/operating proc — Compliance w/ procedure

Sequence of events

5 timed eventsfrom the FDR factual report · claude-sonnet-5
  1. 20:45:40 GMTApproach (initial approach to Bob Hope Airport, Burbank, CA)p.3
    TCAS Down Advisory set "On" followed by a pitch up then a pitch down motion
  2. 20:45:49 GMTApproach (TCAS event)p.3
    TCAS Down Advisory set "Off" and TCAS Up Advisory set "On", accompanied by a pitch up motion
  3. 20:45:51 GMTApproach (TCAS event)p.3
    Minimum recorded vertical acceleration of 0.09 g's
  4. 20:45:52 GMTApproach (TCAS event)p.3
    Maximum recorded vertical acceleration of 2.93 g's
  5. 20:46:10 GMTApproach (TCAS event)p.3
    TCAS Up Advisory set "Off"

NTSB analysis

from the final report

During descent to landing, the flight crew inadvertently turned about 27 degrees off their air traffic controller-assigned heading. When advised by the controller to check the airplane’s heading, the flight crew noted the heading discrepancy and immediately initiated a turn back to the assigned heading. During the turn, the flight crew received a traffic alert and collision avoidance system resolution advisory (RA). The captain responded to the RA by initiating an estimated 1,500- to 2,000-foot-per-minute rate of descent followed by an approximate 2,000-foot-per-minute climb. During the RA response maneuvers, three flight attendants were standing in the aft galley, one of whom was seriously injured.