This is an analysis of the Aircraft Accident Report of the runway overrun and collision of Southwest Airlines Flight 1248. The information contained herein was retrieved from the Accident Report provided by the National Transportation Safety Board and the Federal Aviation Administration. On December 8, 2005 Flight 1248 ran off runway 31C after landing at Chicago Midway International Airport at Chicago, IL. The aircraft rolled through two fences, a blast fence and an airport perimeter fence, before crashing onto an adjacent roadway. Before coming to a stop, the aircraft crashed into a vehicle resulting in the death of a young boy, which was a passenger in the vehicle. The National Transportation Board determined that the probable cause of the accident was the pilots’ failure to use available thrust in a timely matter and lack of familiarity of the aircraft’s auto-brake system. However, there were other factors that may have contributed to the accident:
1) Southwest’s failure to provide its pilots with clear and consistent guidance and training regarding company policies and procedures related to arrival landing distance calculations;
2) Programming and design of its on board performance computer, which did not present inherent assumptions in the program critical to pilot decision-making;
3) Plan to implement new autobrake procedures without a familiarization period; and
4) Failure to include a margin of safety in the arrival assessment to account for operational uncertainties.
Further contributing factors included the pilots’ failure to divert to another airport given reports that included poor braking action and a tailwind component greater than 5 knots. Adding to the severity of the accident was the absence of an engineering materials arresting system. This was needed because of the limited runway safety area beyond the departure end of runway 31C.
The airplane had departed from Baltimore/Washington International Thurgood Marshall Airport (BWI), Baltimore, Maryland, about 1758 Eastern Standard Time (EST). At the time of the accident instrument meteorological conditions existed and the flight operated under an instrument flight rules flight plan. It was a dark and stormy night. The accident occurred on the first flight of the first day of a scheduled 3-day trip. The flight departed BWI about 2 hours late because of worsening weather conditions in the Chicago area. It was reported by the pilots that they had reviewed two reports concerning weather information and dispatch documents before leaving BWI. It was later noted that a third document authorizing the release of flight was prepared but had not been delivered before the departure of the flight. This report had changed the expected landing winds. The braking action reports were also mixed. It reported good or fair braking action for the first part of the runway however, poor braking action for the second half of the runway.
As the aircraft was approaching BWI the Air Traffic Controller (ATC) gave the pilots instruction to enter into a holding pattern. This was due to runway clearing by snowplows. It was determined that Chicago Midway International Airport personnel monitored runway conditions and provided appropriate snow removal service on the night of the accident.
While in this holding pattern the first officer entered the updated weather and runway conditions and wind information (090?? at 11 knots) in the on board performance computer (OPC) to determine the landing distance required for runway 31C. There is an assortment of aids available to pilots when performing airplane performance and landing distance calculations. Options include tabular performance charts and on board electronic computing devices (also known as OPCs at SWA). The FAA evaluates and approves operators’ procedures for the use of electronic computing devices.
The OPC is a laptop computer with which every SWA airplane cockpit is equipped and that SWA pilots use in performing takeoff and landing performance calculations. The OPC display showed 8 knots tail wind however the limit of the OPC was 5T. The NSTB concluded that if the OPC had used the actual tailwind of 8 knots instead of the 5 knot limits, the stopping margin for braking would have shown a negative 260 feet presenting the max stop margin in red instead of the white background it shown. When calculating an 8 knot tail wind the conditions showed as poor. This would have allowed the pilots to accurately access that the runway could not be landed on safely. It was concluded by the Safety Board that if the pilots had been presented with stopping margins associated with the input winds or had known that the stopping margins calculated by the OPC for the 737-700 already assumed credit for the use of thrust reversers, the pilots may have chosen to redirect the flight to another airport. One of the hazards that were previously identified in this course was the use of equipment which is not up to date or relying on equipment that fails to provide the function intended. It was also determined that the BWI Air Traffic Control Tower did not follow Federal Aviation Administration guidance when he did not provide all of the required braking action report information,
On December 8, 2005 at approximately 0620 the National Weather Service (NWS) began issuing snow advisories for the Chicago Metropolitan area and northern Illinois. It continued into the evening hours with increasing snowfall. Less than one hour before the accident, at 1819 the NWS forecast office issued a winter weather advisory that indicated that a heavy snow warning was in affect for the Chicago area until midnight with estimates of 6-9 inches of snow accumulation. Southwest Airline records indicated that the airplane’s original dispatch release was updated three times before the accident flight. The investigation indicated that the revisions resulted from changes in alternate airport destinations, the contingency fuel load, and the planned landing runway at MDW. The accident flight’s release calculations were determined for the use of runway 31C. The release contained two alternate airport destinations and sufficient fuel for the most distant alternate airport with an additional 90 minutes of contingency fuel. The accident runway had been recently cleared and treated with deice fluid, and four other SWA 737-700 airplanes landed and successfully stopped on runway 31C minutes before the accident. However, the aircraft landed in generally deteriorating runway surface conditions which made the flight’s braking ability almost five times worse than would be expected on a bare and dry runway. It is apparent that landing at another airport was an available option.
As ironically as it may appear, Southwest Airlines had plans to implement guidelines which made the use of autobrakes under certain landing conditions on December 12, 2005, only four short days after the accident. The company had disallowed the use of autobrakes because the company’s fleet was not yet fully equipped with autobrakes. As they became available the company then implemented the use of the autobrake. As a preparatory step Southwest had provided pilots with a self-study training module on the use of the autobrake system. Both pilots of the accident flight had completed the self-study training. Southwest provided pilots with bulletins which contained updates concerning the system. A bulletin issued on December 8, 2005, the day of the accident flight, reinstated the autobrake policy and procedures would not begin until December 12, 2005. So while Southwest aircraft were equipped with ‘flow’ cards and checklists with information regarding autobrake procedures use on the date of the accident, December 8, 2005, was unauthorized the day of the accident.
The 737-700 autobrake system was intended to automatically apply brakes upon main landing gear strut compression and wheel spinup after touchdown. The system perceives deceleration during the landing roll and automatically modulates brake pressure as a result. Autobrakes were deactivated about 12 seconds after touchdown, and pilot-commanded brake pressure increased to 3,000 pounds per square inch. The first indication of thrust reverser activity was recorded about 15 seconds after touchdown, with full deployment about 18 seconds after touchdown. During post-accident interviews, the pilots stated they had read the daily read-before-flight (RBF) letters before the accident flight but that they did not notice there was a delay in autobrake procedure implementation. While admitting that they had read the procedure both pilots somehow failed the date of implementation which would not be in effect until four days past the date of the accident.
Another factor identified was the absence of an engineering materials arresting system, which was needed because of the limited runway safety area beyond the departure end of runway. An Engineered Materials Arresting System (EMAS) ‘improves safety benefits in cases where land is not available, or not possible to have the standard 1,000-foot overrun. A standard EMAS installation extends 600 feet from the end of the runway. An EMAS arrestor bed can be installed to help slow or stop an aircraft that overruns the runway, even if less than 600 feet of land is available.'(FAA, 2014). In the present case the aircraft traveled through a blast fence, an airport perimeter fence, and finally onto an adjacent roadway, where it struck an automobile, killing a child, before coming to a complete stop. Needless to say the use of an EMAS in this accident could have saved the life of a child. To date nine accidents have been avoided thanks to the use of an EMAS. Forty-seven airports in the United States have a total of 74 runways in which an EMAS has been installed.
In conclusion, with every accident a lesson is learned with hopes of preventing a future accident. Basically, you are identifying hazards. Hazard one- probable cause of the accident was the pilots’ failure to use available reverse thrust in a timely manner to safely slow or stop the airplane after landing, which resulted in a runway overrun. This failure occurred because the pilots’ first experience and lack of familiarity with the airplane’s autobrake system distracted them from using reverse thrust during the challenging landing. Solution- Extensive training to familiarize pilots with new systems. The NTSB made recommendations to that FAA to require all 14 Code of Federal Regulations Part 121 and 135 operators of thrust reverser-equipped airplanes to incorporate a procedure requiring the non-flying pilot to check and confirm the thrust reverser status immediately after touchdown on all landings. Hazard Two- Southwest Airlines’ failure to provide its pilots with clear and consistent guidance and training regarding company policies related to arrival landing distance calculations. Solution- Training and Communication. Although the pilots in this incident both admitted to reading the material covering autobrakes, both pilots failed to notice the implementation date. This should have been one of the first things listed when pilots reviewed the material. Also some type of sign off should have been completed by pilots who had completed the self-training module covering instruction and implementation date of the system. Also at issue was two different operators were using manufacturer-supplied landing performance data that were not the most suitable or currently available. This was a prime example of the importance of having the most current and suitable equipment available. Hazard Three- plan to implement new autobrake procedures without a familiarization period. Solution ‘ This is another training and communication problem. Providing the self-training module introduced the pilots to the new equipment however, there also needed to be an on-site training certification for all pilots before establishing an implementation date. Hazard Four- failure to include a margin of safety in the arrival assessment to account for operational uncertainties. Solution- This hazard has been recognized by 47 airports in the United States. This is an issue of planning and recognizing airport hazards. A total of 74 runways have installed Engineered Materials Arresting System (EMAS) to prevent accidents just as this one by Southwest Flight 1248. If an EMAS had existed on runway 31C it is probable that the aircraft would not have entered the roadway and collided with the vehicle. While there is nothing that exists that will prevent future accidents, it is vital to investigate causes and find possible solutions from preventing a reoccurrence of an accident.