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155 CHAPTER 15 Conclusions The first research phase engaged in multiple studies of dif- have a notable impact on the size and cost of arrestor systems, ferent topics relevant to developing arrestor alternatives. After irrespective of which passive arrestor technology is used. identifying promising alternatives, several candidate concepts The FAA EMAS design requirements currently prohibit were selected for detailed evaluation in the second experimen- damage to the aircraft, which typically results in arrestor bed tation phase. In the second phase, testing and modeling were designs constrained by the rearward nose-gear loads. More used to evaluate the performance of the candidates. This chap- aggressive decelerations would be possible if the designs were ter summarizes important conclusions from both phases of permitted to collapse the nose gear as long as the main gear research. remained intact. Prior EMAS testing suggests that this may pose minimal hazards to aircraft occupants. However, aircraft with low-slung engines could potentially be damaged and/or 15.1. Study Phase ingest arrestor material in such cases, and the risks of these The survey of U.S. airport operators revealed that actual effects have not been quantified. Additional concerns would EMAS costs appear to exceed the predicted values con- apply to turbo-prop aircraft, where propeller damage could tained in FAA Order 5200.9 in terms of preparatory paving, present additional hazards. It may be advantageous to revisit installation, and maintenance (Chapter 3). While the survey the requirements regarding landing gear loading in order to included more airports than the original data set used to create determine if case-by-case exceptions may be permissible. In Order 5200.9, it did not include all EMAS systems installed at some circumstances, the benefits of aggressive arrestor per- U.S. airports. It is possible that the average costs could shift formance may outweigh the risks of failing to stop an overrun. once the remaining airports were included. However, since The approval and commercialization study determined the survey data for the CTEE was 1.8 times higher than the that the current lack of a general predictive software tool pre- predicted value, an update to the guidance document may sents a barrier for new entrants to the arrestor system field be advisable. (Chapter 6). Development of such a tool, or an update of the A review of aircraft overrun data led to a revised probabil- older ARRESTOR code, could be considered as part of any ity curve for aircraft overrun exit speeds (Chapter 5). This new approval process. revised curve indicated that 90% of aircraft overruns may no Although based on anecdotal experience, the researchers longer take place at or below an exit speed of 70 knots. The have noted a seeming lack of awareness regarding the exis- new curve suggests that the 90% threshold may have shifted tence, usage, and function of EMAS among airline pilots. This to just above 80 knots. This could impact the design speeds lack of awareness has been observed in both newer and sea- for aircraft arrestors if a 90% criterion is to be maintained. soned pilots. It is unclear whether awareness is greater among Additional investigation may be warranted regarding the pilots that typically land at airports with EMAS. Unfortu- accuracy of the reported data that was used in the assessment. nately, response from the pilot community was limited dur- The sensitivity analysis showed that the relative length of ing the survey process. Nevertheless, it may be beneficial to an arrestor bed will tend to vary with the aircraft exit speed consider pursuit of an educational effort to increase aware- squared (Chapter 5). Increasing the 70-knot standard exit ness of the existence and function of EMAS within the pilot speed or the 40-knot minimum exit speed requirements would community.