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144 CHAPTER 13 Summary of Passive System Candidates Chapters 9 through 12 examined the passive system candi- ports, in which arrestor beds are designed as a compromise dates on an individual basis. This brief chapter summarizes between the different aircraft serviced. key findings for performance and cost on a side-by-side basis. Figure 13-1 compares the best single-aircraft bed designs for the three alternatives and compares them to the current EMAS technology. The four sets of bars show very similar 13.1. Overview trends in terms of relative stopping lengths for the different The experimentation phase evaluated three passive arrestor aircraft. The glass foam stopping distances are slightly shorter candidate systems: than those of the current EMAS, while the other two concepts would require slightly longer beds. The performance simi- 1. Glass foam arrestor larity of glass foam and the current EMAS is not surprising 2. Aggregate foam arrestor because both designs use crushable foam block material 3. Engineered aggregate arrestor with similar mechanical behavior. However, this compari- son of single-aircraft performance is ultimately less relevant Each demonstrated relative strengths and weaknesses. All to real applications than the multi-aircraft comparisons that three options provide concepts with increased material dura- follow. bility over cellular cement, which would likely result in longer Figure 13-2 compares the best multi-aircraft arrestor bed life cycles and decreased maintenance requirements. designs for the three alternatives. In each case, the B747-400 required the longest bed for arrestment from a 70-knot exit speed. It should be noted that performance predictions for the 13.2. Performance Comparison existing EMAS have not been included in the figure because The performance of the different candidates can be com- the design cases did not apply to multi-aircraft bed designs. In pared in two primary ways: based on (1) single-plane or general, the material could be assumed to follow a similar (2) multi-aircraft bed designs. When comparing single- trend to glass foam, owing to the mechanical similarities just aircraft bed designs, the thickness of each bed and its mate- discussed. rial properties are optimized for the plane of interest. How- In comparing Figure 13-1 with Figure 13-2, the trend for ever, the bed designs for the different aircraft may not be leading and trailing concepts shifts considerably. The differ- compatible with one another. For example, a best-case design ences illustrate how substantially the multi-aircraft perfor- for the B747-400 was typically found to overload the landing mance deviates from aircraft considered individually. For the gear of the CRJ-200. multi-aircraft case, bars of similar height indicate improved When comparing multi-aircraft bed designs, a single bed is equality in the treatment of the three aircraft. Of the three designed for best-case performance with all three of the subject concepts, the aggregate foam shows the most consistent per- aircraft simultaneously. A single bed thickness and material formance, with dramatic reduction in the stopping distance for property are determined such that the overall performance is the B747-400. optimized for all three aircraft. As an example, for a bed with a practical 400-ft length, the The single-aircraft comparisons always produce the short- exit speeds for each aircraft are as shown in Table 13-1. The est feasible stopping distances. However, the multi-aircraft 400-ft bed would obtain a full 70-knot exit speed rating for comparisons are more relevant to actual applications at air- the CRJ-200 with all arrestor concepts. Both the glass foam