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Southwest Airlines 1455

Accident Case Study

 


 

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Figure: Southwest 1455 N668SW, photo courtesy Joe Pries.

Accident Report

  • Date: 5 March 2000
  • Time: 18:11 PST
  • Type: Boeing 737-3T5
  • Operator: Southwest Airlines
  • Registration: N668SW
  • Fatalities: 0 of 5 crew, 0 of 137 passengers
  • Aircraft Fate: Destroyed
  • Phase: Landing
  • Airports: (Departure) Las Vegas-McCarren International Airport, NY (LAS/KLAS) United States of America; (Destination) Burbank/Glendale/Pasadena Airport, CA (BUR/KBUR) United States of America

Narrative

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Figure: Southwest Airlines 1455 vertical track, from "Pressing the Approach".

[CVR]

  • 1749:46 ATIS-2 [sound similar to ATIS transmission that is unreadable on the CFR recording]
  • The ATIS was: "burbank airport information papa zero one five three zulu wind two four zero at six visibility one zero few clouds at six thousand five hundred ceiling niner thousand overcast temperature niner dew point one altimeter two niner six five i l s runway eight approach in use arriving and departing runway eight and runway one five."

  • 17:50:28 HOT-2 [First Officer] I'm sure glad I'm just watching this leg.
  • 17:51:34 HOT-2 [First Officer] Good day to watch.
  • The first officer had over 2,500 hours in type and appeared to be bothered by the tailwind conditions after listening to the ATIS and receiving their first instructions for the descent. His intuition was telling him something and his words should have told the captain something too.

    More about this: Decision Making.

[NSTB AAB-02/04, pg. 2]

  • At 1802:52, the flight crew was advised by the Southern California terminal radar approach control (SCT) Woodland controller that the current ATIS was information Papa and that they should expect an instrument landing system (ILS) landing on runway 8. At 1803:29, when the airplane was about 20 nautical miles (nm) north of the BUDDE outer marker at an altitude of about 8,000 feet mean sea level (msl), the Woodland controller instructed flight 1455 to turn left to a heading of 190° and to descend to and maintain 6,000 feet msl. The first officer acknowledged the instructions.
  • At 1804:02, when the airplane was about 19 nm north of the BUDDE outer marker at an altitude of about 7,800 feet msl, the SCT Woodland controller stated, "Southwest fourteen fifty five, maintain two thirty or greater til advised please." The captain acknowledged the airspeed adjustment assignment. The Woodland controller indicated in a post accident interview that he imposed the speed restriction as part of sequencing Southwest flight 1455 between Southwest flight 1713 and Executive Jet flight 278.
  • After the first officer obtained information Papa, he switched back to the approach control frequency. At 1804:42, he informed the captain that the target airspeed for the approach would be 138 knots and, at 1804:49, that winds were "down to six knots." A few seconds later, he confirmed that aircraft were landing at BUR on runway 8. At 1805:08, when the airplane was about 16 nm north of the BUDDE outer marker at an altitude of about 6,000 feet msl, the SCT Woodland controller instructed flight 1455 to "turn left heading one six zero." At 1805:13, the captain indicated to the first officer that ATC "wants two hundred thirty knots or greater, for a while."
  • At 1805:54, the SCT Woodland controller cleared flight 1455 to descend to and maintain 5,000 feet and advised the pilots that they were following company traffic (Southwest Airlines flight 1713) that was at their "one o'clock and twelve miles [ahead of them] turning onto the final out of forty six hundred." The first officer acknowledged the clearance. At 1807:43, the Woodland controller cleared flight 1455 to descend to and maintain 3,000 feet. The first officer acknowledged the clearance. At 1808:18, the first officer notified ATC that he had the Southwest traffic in sight. At 1808:19, the Woodland controller issued an altitude restriction by stating, "cross Van Nuys at or above three thousand, cleared visual approach runway eight." The first officer acknowledged the clearance. At 1808:36, as the airplane was descending through about 3,800 feet msl, the captain began turning to the left for the final approach.
  • At this point the speed restriction no longer applies, but the crew missed that and delayed slowing down for almost a minute.

  • In post accident interviews, the flight crew told investigators that, during the approach, the captain's navigation radio was tuned to the ILS frequency for runway 8, and the first officer's radio was tuned to the Van Nuys VOR. They indicated that the autopilot was engaged in the VOR/LOC mode and that the airplane captured the localizer course but then overshot the centerline before correcting back. The captain stated to investigators that as the flight passed about 2 miles west of Van Nuys at 3,000 feet at approximately 220 to 230 knots, he deployed the speed brakes.
  • According to the CVR, at 1809:28, when the airplane was at an indicated airspeed of about 220 knots, the captain called for "flaps five/" At 1809:32, the flaps began to extend. At 1809:43, the captain called for "gear down." The captain indicated in a post accident interview that at this point in the flight, he noted a 20-knot tailwind indication on the flight management system (FMS) screen. At 1809:53, the BUR tower controller stated, "Southwest fourteen fifty five, wind uh . . . two one zero at six [knots], runway eight, cleared to land." Simultaneously, the captain called for "flaps fifteen." At 1810:01, the captain again called for "flaps fifteen" and "[flaps] twenty five."
  • From 1810:24 until 1810:59, the ground proximity warning system (GPWS) alerts were being continuously broadcast in the cockpit, first as "sink rate" and then, at 1810:44, switching to "whoop, whoop, pull up." At 1810:29, the captain stated, "flaps thirty, just put it down." At 1810:33, the captain stated, "put it to [flaps] forty. [I]t won't go, I know that. [I]t's all right. [F]inal descent checklist." After the GPWS "whoop, whoop, pull up" alert sounded at 1810:47, the captain stated, "that's all right," at 1810:53. A final "sink rate' warning was recorded at 1810:55. The first officer stated in a post accident interview that instead of reading the final descent checklist, he visually confirmed the checklist items and remembered seeing the captain arm the ground spoilers. The first officer also stated that when the captain called for flaps 40°, the airspeed was about 180 knots and went as high as 190 knots during the approach. The first officer indicated that he pointed to his airspeed indicator to alert the captain of the flap limit speed of 158 knots at flaps 40°.
  • The captain told Safety Board investigators that he remembered hearing the “sink rate” warning from the GPWS but that he did not react to the warning because he did not feel that he had to take action. He stated that he did not remember any other GPWS warnings during the approach. The first officer indicated in a post accident interview that he heard both the “sink rate” and the “pull up” GPWS warnings but that he believed that the captain was correcting.
  • The first officer also indicated to investigators that he selected the “Progress” page on the FMS cockpit display unit but that he could not recall what the wind values were during the approach. He stated to investigators that he was concerned that the ground speed was faster than normal but added that he did not verbalize his concern to the captain. The first officer further indicated to investigators that he felt that the approach was stabilized and that they were in a position to land.
  • The captain stated in a post accident interview that he was aware that Southwest Airlines’ standard procedure was for the captain and first officer to call “1,000 [feet above ground level (agl)], airspeed, and sink rate” when descending through 1,000 feet. However, no such callouts were recorded by the CVR. The captain also stated in a post accident interview that he visually perceived that the airplane was “fast” as it crossed the approach end of runway. CVR and FDR data indicate that the airplane touched down at 1810:58 with flaps extended to 30° at about 182 knots; flaps then extended to 40° during the ground roll at about 145 knots.
  • The captain stated to Safety Board investigators that after touchdown, the end of the runway appeared to be closer than it should have been and that he thought they might hit the blast fence wall. The captain indicated that he braked “pretty good” while attempting to stop the airplane. FDR data indicate that the captain unlocked the thrust reversers 3.86 seconds after touchdown and that the thrust reversers deployed 4.91 seconds after touchdown. The first officer stated to investigators that the captain applied the wheel brakes before the airplane had decelerated to 80 knots15 and that, as the airplane passed the Southwest Airlines passenger boarding gates, he joined the captain in braking the airplane and applied the brakes as hard as he could. The captain indicated that as the airplane neared the end of the runway, he initiated a right turn using only the nose wheel steering tiller (not the rudder pedals). At 1811:20, the cockpit area microphone (CAM) recorded impact sounds. The airplane departed the right side of the runway about 30° from the runway heading, penetrated a metal blast fence and an airport perimeter wall, and came to a stop on a city street off of the airport property. An emergency evacuation ensued, and all crewmembers and passengers successfully exited the airplane.

Analysis

[NSTB AAB-02/04, pg. 12]

  • The Safety Board conducted an airplane performance study in conjunction with this accident investigation. FDR and radar data indicate that the airplane began its final descent to BUR about 3 nm from the runway 8 threshold. Taking into account the airplane's altitude of 3,000 feet msl at the beginning of the descent and the 725-foot msl elevation of the touchdown zone (TDZ)27 on runway 8, geometry calculations indicate that the airplane would have had to have descended at an average flight path angle of about 7° to touch down in the runway 8 TDZ. Radar and FDR data show that the airplane descended at an average flight path angle of about 7° until flare, at an average vertical speed of 2,200 feet per minute (fpm), and at indicated airspeeds of between 182 and 200 knots. The airplane began to flare about 170 feet agl and flared for about 9 seconds before touching down at 182 knots indicated airspeed on runway 8. Average ground speed during the flare was 195 knots, indicating that the airplane traveled about 3,000 feet during the flare.
  • At the request of the Safety Board’s Airplane Performance Group, Boeing ran stopping distance simulations for this accident wherein maximum, medium, and minimum 737 autobrake applications, as well as maximum manual brake applications, were simulated for wet runway conditions after the 182-knot touchdown. These data indicate that the accident airplane would have required about 5,000 feet of runway length after touchdown to stop using maximum autobrakes and about 4,700 feet of runway length after touchdown to stop using maximum manual brakes. Boeing stopping distance calculations based on FDR acceleration data show that the accident airplane traveled about 4,150 feet from touchdown to impact with the blast fence, indicating that the airplane touched down about 2,150 feet beyond the runway 8 threshold in the TDZ.
  • The Southwest Airlines FOM, “Normal Operations,” “Approach,” “Approach Envelope for All Approaches” (Chapter 3, Section 6), states, in part, the following:
  • Go-around must begin whenever adverse factors have piled up against you and the aircraft is not in the “slot.” . . . Entry Slot 1000’ AGL Landing Gear Down Final Flaps Final “Slot” Conditions Proper sink rate and on glide path Proper speed (for existing conditions) Proper runway alignment -- no further turning required . . . Trimmed for zero stick forces; Steady-state thrust setting In final landing configuration IF NOT IN THE “SLOT,” YOU ARE NOT PREPARED FOR A NORMAL LANDING.

  • The Southwest Airlines FOM, “Normal Operations,” “Approach,” “Go-around and Missed Approach” (Chapter 3, Section 6), states, in part, the following:
  • Go-around/missed approach procedures have been designed to make execution of the procedure as simple as possible. The procedure is nearly the same for every profile. . . A missed approach must be executed if . . . the pilot determines that a landing cannot be safely accomplished in the touchdown zone.

  • A comparison of the recorded radar data of the accident airplane to 70 other airplanes that had landed at BUR on runway 8 between 1000 and 2200 on June 13 and 14, 2000, showed that of the 16 airplanes vectored from the north side of BUR to land on runway 8, 12 were vectored to intercept the final approach course between 9 and 15 nm west of the runway threshold. Flight 1455 was given vectors that resulted in interception of the final approach course about 8 nm west of the runway threshold. The comparison also showed that the glidepaths of most airplanes approaching runway 8 were between 3° and 4°. The accident airplane's glidepath was 7°.
  • In summary, the Safety Board concludes that the actions of the SCT Woodland controller positioned the airplane too fast, too high, and too close to the runway threshold to leave any safe options other than a go-around maneuver.

Probable Cause

[NSTB AAB-02/04, pg. 23] The National Transportation Safety Board determines that the probable cause of this accident was the flight crew's excessive airspeed and flightpath angle during the approach and landing and its failure to abort the approach when stabilized approach criteria were not met. Contributing to the accident was the controllerís positioning of the airplane in such a manner as to leave no safe options for the flight crew other than a go-around maneuver.

See Also

Decision Making

Stabilized Approach

References

Flight Safety Foundation, Aviation Safety World, "Pressing the Approach," December 2006

NTSB Aircraft Accident Brief, AAB-02/04, Southwest Airlines Flight 1455, Boeing 737-300, N668SW, Burbank, California, March 5, 2000

NTSB Specialists Factual Report of Investigation, DCA00MA030, Cockpit Voice Recorder, April 20, 2000

Revision: 20150501
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