BOEING 737 7H4SOUTHWEST AIRLINES CO
Flushing, NY, USA · 2013-07-22·N753SW
What happened
NTSB summary, verbatimAs the airplane was on final approach, the captain, who was the pilot monitoring (PM), realized that the flaps were not configured as had been briefed, with a setting of 40 degrees for the landing. Data from the flight data recorder (FDR) indicate that the captain set the flaps to 40 degrees as the airplane was descending through about 500 ft altitude, which was about 51 seconds from touchdown. When the airplane was between 100 to 200 ft altitude, it was above the glideslope. Concerned that the airplane was too high, the captain exclaimed repeatedly "get down" to the first officer about 9 seconds from touchdown. About 3 seconds from touchdown when the airplane was about 27 ft altitude, the captain announced "I got it," indicating that she was taking control of the airplane, and the first officer replied, "ok, you got it." According to FDR data, after the captain took control, the control column was relaxed to a neutral position and the throttles were not advanced until about 1 second before touchdown. The airplane touched down at a descent rate of 960 ft per minute and a nose-down pitch attitude of -3.1 degrees, resulting in the nose gear contacting the runway first and a hard landing. The airplane came to a stop on the right side of the runway centerline about 2,500 ft from its initial touchdown. The operator's stabilized approach criteria require an immediate go-around if the airplane flaps or landing gear were not in the final landing configuration by 1,000 ft above the touchdown zone; in this case, the flaps were not correctly configured until the airplane was passing through 500 ft. Further, the airplane's deviation about the glideslope at 100 to 200 ft would have been another opportunity for the captain, as the PM at this point during the flight, to call for a go-around, as indicated in the Southwest Airlines Flight Operations Manual (FOM). Accident data suggest that pilots often fail to perform a go-around or missed approach when stabilized approach criteria are not met. A review of NTSB-investigated accidents by human factors researchers found that about 75% of accidents were the result of plan continuation errors in which the crew continued an approach despite cues that suggested it should not be continued. Additionally, line operations safety audit data presented at the International Air Safety Summit in 2011 suggested that 97% of unstabilized approaches were continued to landing even though doing so was in violation of companies' standard operating procedures (SOPs). The Southwest FOM also states that the captain can take control of the airplane for safety reasons; however, the captain's decision to take control of the airplane at 27 ft above the ground did not allow her adequate time to correct the airplane's deteriorating energy state and prevent the nose landing gear from striking the runway. The late transfer of control resulted in neither pilot being able to effectively monitor the airplane's altitude and attitude. The first officer reported that, after the captain took control of the airplane, he scanned the altimeter and airspeed to gain situational awareness but that he became distracted by the runway "rushing" up to them and "there was no time to say anything." The captain should have called for a go-around when it was apparent that the approach was unstabilized well before the point that she attempted to salvage the landing by taking control of the airplane at a very low altitude. In addition, the captain did not follow SOPs at several points during the flight. As PM, she should have made the standard callout per the Southwest FOM when the airplane was above glideslope, stating "glideslope" and adding a descriptive word or words to the callout (for example, "one dot high"). Rather than make this callout, however, the captain repeatedly said "get down" to the first officer before stating "I got it." The way she handled the transfer of airplane control was also contrary to the FOM, which indicates that the PM should say "I have the aircraft." The flight crew's performance was indicative of poor crew resource management.
Photographs
11the aircraft, and what the investigators foundPhotographs are NTSB docket attachments — works of the US government, in the public domain. Captions are the Board’s own.
Probable cause
the Board's determinationThe captain's attempt to recover from an unstabilized approach by transferring airplane control at low altitude instead of performing a go-around. Contributing to the accident was the captain's failure to comply with standard operating procedures.
Occurrence sequence
2 stepsNTSB coding · CICTT taxonomy- 1 · Landing-flare/touchdownHard landingdefining event
- 2 · Landing-flare/touchdownLanding gear collapse
Findings
3 causal · 0 contributing- CAUSEAircraft › Aircraft oper/perf/capability › Performance/control parameters › Descent/approach/glide path — Not attained/maintained
- CAUSEPersonnel issues › Action/decision › Action › Lack of action — Pilot
- CAUSEPersonnel issues › Task performance › Use of equip/info › Use of policy/procedure — Pilot
Sequence of events
9 timed eventsfrom the FDR factual report · claude-fable-5-1 (in-session)- 15:37:25-15:49:12 EDTpre-flightp.3On the ground at Nashville between flight control check and takeoff roll, control column position biases of -0.47 (captain) and 0.58 (first officer) and average force transducer readings of -0.84 lb (captain) and -3.03 lb (first officer) were determined and offset to identify the pilot flying
- 17:41:00 EDTapproachp.4Start of plotted approach: autopilot engaged, autothrottle in MCP speed mode with 210 knots selected as the heading intercepts the runway 04 localizer; descent begins from the 2,700 ft MSL step-down altitude
- 17:41:14 EDTapproachp.4MCP selected airspeed decreased to 180 knots while descending on glideslope; changed to 150 knots at 17:41:54 and to 134 knots at 17:42:36, where it remained
- 17:43:49 EDTapproachp.4Autothrottle disengaged for the remainder of the flight
- 17:43:50 EDTfinal approachp.4Autopilot disengaged; radio altitude between 385 and 361 ft, pressure altitude roughly 470 ft MSL; aircraft tracking the runway heading of around 044 degrees; control column data show the pilot flying manipulating the controls, with the first officer's column force transducer reading greater than the captain's in both push and pull
- 17:44:11 EDTfinal approachp.4ILS glideslope deviation began a fly-down trend (aircraft above glideslope), reaching a maximum at 17:44:23 just before touchdown; just before the maximum, captain and first officer column forces became closely aligned
- before touchdownfinal approachp.4Engine 1 and 2 throttle resolver angles decreased to around 35 degrees with N1 following a decreasing trend; pitch entered a nose-down trend reaching a minimum airborne value of -3.87 degrees; column positions near zero just before touchdown
- 17:44:27 EDTlandingp.4Touchdown with vertical acceleration peaking at 3.18 g
- 17:44:46 EDTlandingp.4Aircraft came to rest
NTSB analysis
from the final reportAs the airplane was on final approach, the captain, who was the pilot monitoring (PM), realized that the flaps were not configured as had been briefed, with a setting of 40 degrees for the landing. Data from the flight data recorder (FDR) indicate that the captain set the flaps to 40 degrees as the airplane was descending through about 500 ft altitude, which was about 51 seconds from touchdown. When the airplane was between 100 to 200 ft altitude, it was above the glideslope. Concerned that the airplane was too high, the captain exclaimed repeatedly "get down" to the first officer about 9 seconds from touchdown. About 3 seconds from touchdown when the airplane was about 27 ft altitude, the captain announced "I got it," indicating that she was taking control of the airplane, and the first officer replied, "ok, you got it." According to FDR data, after the captain took control, the control column was relaxed to a neutral position and the throttles were not advanced until about 1 second before touchdown. The airplane touched down at a descent rate of 960 ft per minute and a nose-down pitch attitude of -3.1 degrees, resulting in the nose gear contacting the runway first and a hard landing. The airplane came to a stop on the right side of the runway centerline about 2,500 ft from its initial touchdown. The operator's stabilized approach criteria require an immediate go-around if the airplane flaps or landing gear were not in the final landing configuration by 1,000 ft above the touchdown zone; in this case, the flaps were not correctly configured until the airplane was passing through 500 ft. Further, the airplane's deviation about the glideslope at 100 to 200 ft would have been another opportunity for the captain, as the PM at this point during the flight, to call for a go-around, as indicated in the Southwest Airlines Flight Operations Manual (FOM). Accident data suggest that pilots often fail to perform a go-around or missed approach when stabilized approach criteria are not met. A review of NTSB-investigated accidents by human factors researchers found that about 75% of accidents were the result of plan continuation errors in which the crew continued an approach despite cues that suggested it should not be continued. Additionally, line operations safety audit data presented at the International Air Safety Summit in 2011 suggested that 97% of unstabilized approaches were continued to landing even though doing so was in violation of companies' standard operating procedures (SOPs). The Southwest FOM also states that the captain can take control of the airplane for safety reasons; however, the captain's decision to take control of the airplane at 27 ft above the ground did not allow her adequate time to correct the airplane's deteriorating energy state and prevent the nose landing gear from striking the runway. The late transfer of control resulted in neither pilot being able to effectively monitor the airplane's altitude and attitude. The first officer reported that, after the captain took control of the airplane, he scanned the altimeter and airspeed to gain situational awareness but that he became distracted by the runway "rushing" up to them and "there was no time to say anything." The captain should have called for a go-around when it was apparent that the approach was unstabilized well before the point that she attempted to salvage the landing by taking control of the airplane at a very low altitude. In addition, the captain did not follow SOPs at several points during the flight. As PM, she should have made the standard callout per the Southwest FOM when the airplane was above glideslope, stating "glideslope" and adding a descriptive word or words to the callout (for example, "one dot high"). Rather than make this callout, however, the captain repeatedly said "get down" to the first officer before stating "I got it." The way she handled the transfer of airplane control was also contrary to the FOM, which indicates that the PM should say "I have the aircraft." The flight crew's performance was indicative of poor crew resource management.