Liberty U – AVIA 305 Week 6 Essay
Southwest Airlines Flight 1248 landing accident (NTSB/AAB-06/03).
This essay will examine landing accident to Southwest Airlines Flight 1248 at Chicago O’Hare airport on December 8th 2005. A search of the NTSB accident/incident database reveals ten runway overrun accidents or incidents since 1982. The NTSB accident report highlights major systemic failures, which will be highlighted below.
Determination of Cause
The National Transportation Safety Board determined that the probable cause of this 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 thrust reverser usage during the challenging landing.
Contributory Causal Factors
The factors that contributed to the accident or contributed to the severity of the accident are:
- Failure to provide its pilots with clear and consistent guidance and training regarding company policies and procedures related to arrival landing distance calculations;
- Programming and design of an on board performance computer, which did not present inherent assumptions in the program critical to pilot decision-making;
- Plan to implement new autobrake procedures without a familiarization period;
- Failure to include a margin of safety in the arrival assessment to account for operational uncertainties;
- Pilots’ failure to divert to another airport given reports that included poor braking action and a tailwind component greater than 5 knots;
- Contributing to the severity of the accident 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 31C.
Under regulation in force at the time of the accident, air carriers were required to provide landing performance calculations prior to departure to ensure adequate landing distance considering aircraft weight, forecast weather and runway conditions, and the expected fuel burn en route. Less than half of the airlines required an arrival landing distance assessment using current data. However, Southwest required their pilots to perform an arrival assessment. The pilots carried out such an assessment using an onboard personal computer with data and algorithms provided by a third party vendor.
However, critical assumptions, specifically the tailwind component of 8 knots, was not used by the computer, inserting the 5 knot tailwind limit imposed in the Flight Operations Manual (FOM). In addition the FOM required pilots to use the worse of mixed runway conditions, as in this case… fair/poor.
Taking all the above critical data into account the pilots were required to divert to an alternate and failed to do so. It must be noted that five similar airliners, some Southwest Airlines operated, had landed safely prior to the accident aircraft.
Conduct of the landing.
Neither pilot had used autobrake, although they had completed ground training. They discussed the autobrake during the approach briefing phase of flight, and clearly were aware of its use. However, after a seemingly normal if fast approach due to the 8-knot tailwind, and after a firm touchdown, the flying pilot failed to engage reverse thrust being concerned with the performance of the brakes. He elected to use manual braking and applied full brake pressure. It was some 15 seconds after touchdown that the monitoring pilot noticed the lack of reverse thrust, and he removed the captain’s hand from the engine levers and selected full reverse thrust. Both full reverse thrust and full wheel braking were applied from then on.
Using all available data, and analyzing the flight data recorder, manufacturer’s landing data, and the reported runway conditions worst case of poor, it is true that a safe landing could have been performed.
This was an avoidable accident.
Poor regulation, poor operational procedures, poor training, inadequate computer display of critical information, confusion amongst pilots as to the significance of landing performance calculations, ignorance of published company procedures, and introduction of autobrake without familiarization all contributed to this accident. Had any one of those factors been correct at the time of this accident, it is entirely possible that one of the links in the chain of events could bave been broken, thus preventing such a tragedy.