Chicago, IL, USA
N799SW
BOEING 737-7Q8
The flight was routine until nearing the Chicago terminal area, where delays due to traffic, weather, and conflicting approaches with O’Hare International Airport resulted in an air traffic controller instructing the flight crew to expect to hold. Shortly afterward, the controller advised the crew that aircraft capable of required navigation performance (RNP) approaches to runway 13C would be accepted to MDW. The flight crewmembers mistakenly loaded and briefed a different procedure, the area navigation (RNAV) global positioning system (GPS) approach, before entering the holding pattern. While in the holding pattern, the flight crew performed a landing distance assessment using the onboard performance computer (OPC). The calculation results showed sufficient runway length for the landing in accordance with the flight manual procedures. Data from the cockpit voice recorder and the OPC indicate that the crew performed the assessment correctly. After receiving air traffic control (ATC) clearance to leave the holding pattern and begin the approach to MDW, the flight crewmembers discussed confusion about the approach instruction, likely because they had loaded and briefed the wrong approach procedure. The flight crew then identified the proper approach procedure chart. The crew subsequently reprogrammed the flight management system for the correct approach and amended some of the procedure crossing altitudes in order to follow ATC instructions. These activities at this point in the approach resulted in extra workload for the flight crew. Later, as flight 1919 neared the runway, the flight crew set flaps to 15. The flight crew of a preceding Southwest Airlines 737 arrival reported “fair” braking action on runway 13C to ATC. The air traffic controller did not advise the flight 1919 crew of the braking action report transmitted by the previous arrival; however, the incident crew overheard the report and correctly recalculated the landing distance assessment, which again indicated sufficient runway length available. The incident crew also set the airplane autobrakes appropriately for the conditions. In addition to discussion regarding the approach procedure automation, the crew had additional operational distractions in the final minutes of the approach. These included a momentary flap overspeed as the first officer attempted to set flaps to 25, assessment of a rain shower passing over the airport, and incorrect settings for minimum altitude reminders. The delay in setting flaps to 25 as the first officer waited for airspeed to decay occurred about the same time that the crew normally should have been executing the Before Landing checklist, which includes the item “speedbrake—armed.” No mention of speedbrakes or the Before Landing checklist is heard on the cockpit voice recording, and data from the flight data recorder (FDR) indicate that the speedbrakes were not armed. The airplane touched down within 500 feet of the runway threshold. After touchdown, the captain perceived a lack of braking effectiveness and quickly applied full manual brakes. Speedbrakes did not deploy upon touchdown, nor were thrust reversers deployed. About 16 seconds after touchdown, thrust reversers were manually deployed, which also resulted in speedbrake deployment per system design, when the airplane had about 1,500 feet of runway remaining. As the airplane neared the end of the pavement, the captain attempted to turn onto the connecting taxiway but was unable. The airplane struck a taxiway light and rolled about 200 feet into the grass. FDR data and component examination revealed that all airplane systems operated as expected. The automatic speedbrakes were not armed and, therefore, would not deploy upon touchdown without crew action. Extending the speedbrakes after landing increases aerodynamic drag and reduces lift, which increases the load applied to the main gear tires and makes the wheel brakes more effective. A lack of speedbrake deployment results in severely degraded stopping ability. According to the flight operations manual, braking effectiveness is reduced by as much as 60 percent. The flight crew’s delay in applying reverse thrust also contributed to the amount of runway used. Simulation studies concluded that the airplane would have stopped with about 900 feet of runway remaining if the speedbrakes had been deployed at touchdown (without reverse thrust) or with about 1,950 feet remaining if both speedbrakes and reverse thrust had been deployed at touchdown, per standard procedures. The calculated braking coefficient of the incident airplane was consistent with a “fair” braking action report, as given by the preceding Southwest Airlines 737 arrival. The braking coefficient is also in accordance with the OPC calculations.
HISTORY OF FLIGHT On April 26, 2011, about 1333 central daylight time (CDT), a Boeing 737-7Q8, registration N799SW, operated by Southwest Airlines as flight 1919, exited the left side of the pavement near the departure end of runway 13C after landing at Chicago Midway International Airport (MDW), Chicago, Illinois. The flight was a regularly scheduled passenger flight from Denver International Airport, Denver Colorado, operating under the provisions of 14 Code of Federal Regulations (CFR) Part 121. There were no injuries to the 134 passengers, including 5 lap-held children, or the 5 crewmembers. The airplane sustained minor damage to the left and right engines and the inboard aft flaps. The crew and operator reported the flight to be routine until nearing the Chicago terminal area. About 1232, the Chicago Approach Control (C90) air traffic controller advised of delays into the Chicago area and that arrivals would be using required navigation performance (RNP) approaches. The crew began to brief the area navigation (RNAV) global positioning system (GPS) Z approach, instead of the RNP approach, and discussed how to set up the flight management system (FMS). At 1238, the flight crew performed the descent checklist, which included setting and cross-checking altimeters and bugs, setting the reference and target airspeeds (to 129 and 145 knots, respectively). The crewmembers stated that they selected autobrakes to “MAX” as indicated by the onboard performance computer (OPC) Landing Output and in accordance with Southwest Airlines Flight Operations Manual (FOM). About 1240, C90 instructed the flight to hold at the SMARS waypoint due to traffic congestion and conflicting traffic patterns with Chicago O’Hare International Airport. While entering and during the hold, the crew discussed fuel and diversion options. About 1256, the crew received ATIS (automated terminal information service) Oscar, observation time 1251 CDT, wind 190 degrees at 16 knots, gusts to 23 knots, visibility 6 statute miles in light rain and mist. Clouds at 800 feet scattered, ceiling 1,400 feet broken, 2,200 feet overcast, temperature 16ºC, dew point 14ºC, altimeter setting 29.40 inches of mercury. The recording stated that the instrument landing system (ILS) for runway 13C was in use, landing and departing runway 13 (sic), departing runway 22L. The recording also included numerous NOTAMs not pertinent to the incident. Following the receipt of the weather, the crew began performing landing distance calculations using the OPC. The initial entry included a landing weight of 127,000 pounds, wet runway with good braking action, and thrust reverse at detent 2. According to the Southwest Flight Reference Manual (FRM) and FOM, the OPC approximate stopping margin calculation was based on minimum, medium, and maximum braking and corresponded to three different autobrake settings (2, 3, and MAX). The FOM also provided guidance on approximating the autobrake actions when using manual braking. Each stop margin calculation included a 1,500-foot air distance from threshold to touchdown and an extra 15 percent distance factor. Stop margin was the distance remaining after the aircraft comes to a complete stop, measured from the nose gear to the end of the available runway. The landing output for maximum braking (autobrake MAX) produced a positive margin of 690 feet. Entering minimum (autobrake 2) or medium braking (autobrake 3) did not provide a positive stopping margin. The crew also performed another calculation with the same inputs except for a 126,000-pound landing weight, and the margin with maximum braking was 720 feet. About 1314, C90 began accepting RNP-capable aircraft destined to MDW. The incident flight was third in the sequence, following another Southwest 737 and a general aviation Citation jet. At 1319, the crew reported to C90 that they were level at 6,000 feet, indicating an airspeed of 210 knots and had received information “Oscar.” The controller advised the crew to expect the RNAV (RNP) Y 13C approach and to slow to 170 knots for traffic sequencing. The controller subsequently cleared the flight direct to the Joliet waypoint (geographically coincident with the Joliet very high frequency omnirange (VOR) navigation aid) and stated “at Joliet intercept the final approach course.” The crew acknowledged the instruction but discussed some confusion about it, likely because Joliet does not appear on the RNAV GPS Z approach chart; rather, it is the RNAV (RNP) Y 13C initial approach fix, beginning the initial approach segment, which had a track of approximately 90 degrees to the final approach course. About 1320, after a brief discussion, the crew set flaps to “2” and then further discussed the controller’s instructions. The crew then identified the proper approach procedure chart and reconciled the instructions with the chart. C90 instructed the crew to descend to 2,500 feet after completing the speed reduction to 170 knots. The RNAV (RNP) Y 13C chart noted a minimum altitude of 4,000 feet after Joliet and a mandatory crossing altitude of 4,000 feet at TOYUL waypoint. The crew acknowledged the controller’s instruction and began briefing and configuring the FMS for the RNAV (RNP) Y 13C procedure. About 1325, the preceding Southwest 737 landed, which was the first arrival on runway 13C in the previous 25 minutes. At 1326:36, the controller stated “Southwest 1919, three miles from TOYUL, cleared for RNAV RNP Y runway one three center approach Midway, maintain 170 knots.” The crew acknowledged and discussed the weather radar display and the nearby rain showers. At 1328:37, C90 instructed the incident flight to maintain 170 knots until JUPIR waypoint and to contact the MDW airport traffic control tower local controller (LC). The crew acknowledged and began to monitor the LC radio frequency. At this time, the crew was discussing symbology and information on the flight instrument displays regarding the approach procedure. At 1329:26, the crew selected landing gear down and flaps 15. The preceding Southwest crew was taxiing clear of the runway and reported the runway was wet with fair braking action. LC relayed the braking report to the pilot of the Citation jet. At 1330:22, the LC controller was relieved by another controller, and the braking report was not included in the position relief briefing or passed to the incident crew. However, the incident crew overheard the runway condition report and made new entries into the OPC. Using the wet runway, fair braking action input, with a 126,000-pound landing weight and maximum reverse thrust and braking, the OPC calculated a landing with 210 feet of margin. About the same time, the crew attempted to set flaps to 25 but noted the airspeed was too high for that setting. Shortly after, the crew selected flaps 30 then, almost immediately, flaps 40. The Southwest Airlines B737-700 Normal Checklist “Before Landing” section reads: “Speedbrake - Armed, Green Light; Landing gear- Down, 3 Green; Flaps – [appropriate setting], Green Light.” Neither the phrase “before landing checklist” nor any mention of “speedbrake” were heard on the cockpit voice recording. The Southwest Airlines FOM stated the before landing checklist should be completed no later than 1,000 feet above touchdown zone elevation and after landing flaps are set. At 1330:44, the incident crew reported passing the JUPIR waypoint inbound and asked LC the direction in which a rain shower was moving. LC responded with an advisory about the traffic they were to follow and landing clearance for runway 13C and advised that the wind was 210 degrees at 9 knots and that the rain was moving to the east-northeast. The crew acknowledged. Beginning about 1331, the crew further discussed the approach procedure; at 1331:37, the captain stated that the airplane was approaching minimums, which was followed by discussion with the first officer about the altimeter display. This discussion ended with the first officer stating, “I'd set mine wrong.” At this point, the airplane was still about 1,000 feet above the runway (about 1,454 mean sea level). Decision altitude for the approach was 1,065 feet above mean sea level, or 454 feet above the runway touchdown zone. At 1333:05, the airplane touched down on runway 13C at an airspeed of 136 knots and a groundspeed of 143 knots. The touchdown occurred within 500 feet of the displaced arrival threshold of the runway, leaving approximately 5,600 feet of runway available for rollout. At the same time, LC advised a following airplane that the wind was from 220 degrees at 10 knots, gusting to 17 knots. Flight data recorder (FDR) information shows that, upon touchdown, the autobrakes indicated “applied” and both main landing gear brake pressures began to increase. After about 1 second, the autobrake parameter indicated “No Auto Brk” while the pilot commanded brake pressure continued to increase (without any fluctuations) up to about 3,000 pounds per square inch (psi), where it remained for the rest of the landing. The crewmembers reported that they applied maximum manual braking shortly after touchdown because of a perceived lack of braking effectiveness; cockpit voice recorder (CVR) evidence is consistent with this report. High manual brake pressure will release the autobrakes and disarm the autobrake system per system design. Anti-skid braking capability is not affected. About 8 seconds after touchdown, the captain stated “I got no brakes”, and the first officer advised he was also applying brakes. About 15 seconds after touchdown, one of the pilots commented about the power, and, about 10 seconds later, a sound similar to increasing reverse thrust is heard. FDR data indicate that throughout the final approach, touchdown, and initial rollout, the speedbrake handle remained at 0 degrees (not armed) and the speedbrake “armed” light was not illuminated. The speedbrake handle remained in its down position upon touchdown and for the first 16 seconds of the landing rollout. Southwest FOM guidance states: “On initial landing roll, braking effectiveness is reduced by as much as 60 percent without speedbrake deployment.” FDR and video data also indicate that the spoilers did not deploy until approximately 17 seconds after touchdown, when the airplane was about 4,600 feet beyond the runway displaced threshold. There are four flight and two ground spoilers on each wing, controlled by the speedbrake system, and normally all the spoilers deploy upon touchdown. FDR and system data indicate that between 15 and 20 seconds after touchdown, the reverse thrust levers were moved to deploy the thrust reversers, which also caused the spoilers to automatically deploy. About 16 seconds after touchdown, the value for the left throttle resolver angle (TRA) increased from its idle position up to a value slightly less than 44 degrees, indicating that this thrust lever had moved forward of its idle position; the value for the right TRA began decreasing from 36 degrees to 24 degrees, indicating that this thrust lever remained in idle and its reverse lever had been activated towards idle reverse. The speedbrake handle began to extend, the speedbrake “armed” light illuminated, and the spoilers began to deploy. For a short period, the value for the left TRA increased from a value of about 44 degrees up to a value slightly greater than 50 degrees. According to the speedbrake system logic, if the value for any TRA exceeds 44 degrees, the auto speedbrake system will command the spoiler actuators to retract. At this time, during the speedbrake handle extension, the rate of the handle movement decreased, at a handle position of about 20 degrees. As the left TRA decreased from about 50 degrees to a value slightly less than 24 degrees, the data indicate that the speedbrake handle was fully extended, the speedbrake “armed” light remained illuminated, and the spoilers were fully deployed. By this time, about 1333:25, both reverser levers were also moving toward the maximum reverse position and engine power began to increase. At the time the spoilers deployed, the airplane had travelled about 4,150 feet from the touchdown point. About 3 seconds later, the thrust reversers indicated deployed, and the airplane was travelling about 92 knots groundspeed at 4,350 feet from touchdown, with about 1,259 feet of runway remaining. The engines spooled up to full power by the time the airplane had 250 feet of runway remaining and had slowed to 55 knots. The airplane heading began to move slightly left of runway heading, and, by 1333:34, the heading had diverged by more than 10 degrees and continued left to about 35 degrees left of runway heading. The captain stated that he attempted to turn the airplane onto the last taxiway on the left side of the runway, but the airplane was still moving too fast to make the turn. At 1333:35, a rumbling sound consistent with the airplane leaving the pavement was heard on the CVR. The airplane left the paved surface at about 30 knots groundspeed, with thrust reversers fully deployed and engine power at or near maximum. Spoilers were deployed and pilot-commanded brake pressure indicated the maximum value of 3,000 psi. The reversers were stowed, power was reduced, and the speedbrake handle retracted as the airplane decelerated in the grass through about 10 to 15 knots. Commanded brake pressure remained at 3,000 psi until the end of the data. By 1333:44, the airplane had come to a stop, about 180 feet beyond and left of the runway end in a soft grassy area, north of the engineered materials arresting system (EMAS). At 1333:48, the captain made a cabin announcement advising the passengers to remain in their seats. At 1334:07, the crew ascertained there was no fire, and advised the passengers that stairs would be on the way to allow them to deplane. At 1334:00, the pilot advised LC that the airplane was in the grass. LC acknowledged and advised him that the emergency vehicles were on the way. Between 1334:30 and 1339:00, the crew discussed the airplane configuration, the stairs and passenger egress, and further discussion about configuration and landing distance. Another OPC calculation was performed, identical to the previous entry. The passengers and crew exited the airplane via airstairs and were bused to the terminal. INJURIES TO PERSONS There were no injuries to the 134 passengers, including 5 lap-held children, or the 5 crewmembers. DAMAGE TO AIRCRAFT The right engine sustained damage from ingesting a taxiway light, and the thrust reverser and inlet cowls were damaged. Two fan blades of the left engine were bent. The left and right inboard aft flaps were damaged. The damage did not meet the 49 CFR Part 830 definition of “substantial.” OTHER DAMAGE One taxiway light was ingested by the right engine. PERSONNEL INFORMATION The captain, age 50, was hired by Southwest Airlines in January 1993. He upgraded to captain about 3 years later and, at the time of the incident, he also held the position of check airman. He was based at Baltimore, Maryland, and earned his commercial and instrument pilot certificates before joining the U.S. Air Force, where he was an instructor pilot and flew C130s. The captain reported approximately 10,500 hours total time, including about 7,000 hours as pilot-in-command and 7,000 hours in the B737 (which included about 5,000 hours as pilot-in-command). There were no records or reports of any previous aviation incidents or accidents involving the captain. A search of the National Driver Register found no record of driver’s license suspension or revocation. The captain held a valid Federal Aviation Administration (FAA) airline transport pilot (ATP) certificate with type ratings for L382 and B737, and a current FAA first-class medical certificate. There were no testing or checking failures in the FAA records. Training and proficiency checks were current, and the company reported that the captain had no unsatisfactory proficiency checks or line checks. The first officer, age 50, was hired by Southwest Airlines in July 2002. He was also based at Baltimore. He flew various ge
The flight crew's delayed deployment of the speedbrakes and thrust reversers, resulting in insufficient runway remaining to bring the airplane to a stop. Contributing to the delay in deployment of these stopping devices was the flight crew's inadequate monitoring of the airplane's configuration after touchdown, likely as a result of being distracted by a perceived lack of wheel braking effectiveness. Contributing to the incident was the flight crew's omission of the Before Landing checklist, which includes an item to verify speedbrake arming before touchdown, as a result of workload and operational distractions during the approach phase of flight.
Source: NTSB Aviation Accident Database
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