National Academies Press: OpenBook

Developing Improved Civil Aircraft Arresting Systems (2009)

Chapter: Chapter 15 - Conclusions

« Previous: Chapter 14 - Main-Gear Engagement Active System Concept
Page 155
Suggested Citation:"Chapter 15 - Conclusions." National Academies of Sciences, Engineering, and Medicine. 2009. Developing Improved Civil Aircraft Arresting Systems. Washington, DC: The National Academies Press. doi: 10.17226/14340.
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Page 155
Page 156
Suggested Citation:"Chapter 15 - Conclusions." National Academies of Sciences, Engineering, and Medicine. 2009. Developing Improved Civil Aircraft Arresting Systems. Washington, DC: The National Academies Press. doi: 10.17226/14340.
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Page 156
Page 157
Suggested Citation:"Chapter 15 - Conclusions." National Academies of Sciences, Engineering, and Medicine. 2009. Developing Improved Civil Aircraft Arresting Systems. Washington, DC: The National Academies Press. doi: 10.17226/14340.
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Page 157

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155 The first research phase engaged in multiple studies of dif- ferent topics relevant to developing arrestor alternatives. After identifying promising alternatives, several candidate concepts were selected for detailed evaluation in the second experimen- tation phase. In the second phase, testing and modeling were used to evaluate the performance of the candidates. This chap- ter summarizes important conclusions from both phases of research. 15.1. Study Phase The survey of U.S. airport operators revealed that actual EMAS costs appear to exceed the predicted values con- tained in FAA Order 5200.9 in terms of preparatory paving, installation, and maintenance (Chapter 3). While the survey included more airports than the original data set used to create Order 5200.9, it did not include all EMAS systems installed at U.S. airports. It is possible that the average costs could shift once the remaining airports were included. However, since the survey data for the CTEE was 1.8 times higher than the predicted value, an update to the guidance document may be advisable. A review of aircraft overrun data led to a revised probabil- ity curve for aircraft overrun exit speeds (Chapter 5). This revised curve indicated that 90% of aircraft overruns may no longer take place at or below an exit speed of 70 knots. The new curve suggests that the 90% threshold may have shifted to just above 80 knots. This could impact the design speeds for aircraft arrestors if a 90% criterion is to be maintained. Additional investigation may be warranted regarding the accuracy of the reported data that was used in the assessment. The sensitivity analysis showed that the relative length of an arrestor bed will tend to vary with the aircraft exit speed squared (Chapter 5). Increasing the 70-knot standard exit speed or the 40-knot minimum exit speed requirements would have a notable impact on the size and cost of arrestor systems, irrespective of which passive arrestor technology is used. The FAA EMAS design requirements currently prohibit damage to the aircraft, which typically results in arrestor bed designs constrained by the rearward nose-gear loads. More aggressive decelerations would be possible if the designs were permitted to collapse the nose gear as long as the main gear 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 ingest arrestor material in such cases, and the risks of these effects have not been quantified. Additional concerns would apply to turbo-prop aircraft, where propeller damage could present additional hazards. It may be advantageous to revisit the requirements regarding landing gear loading in order to determine if case-by-case exceptions may be permissible. In some circumstances, the benefits of aggressive arrestor per- formance may outweigh the risks of failing to stop an overrun. The approval and commercialization study determined that the current lack of a general predictive software tool pre- sents a barrier for new entrants to the arrestor system field (Chapter 6). Development of such a tool, or an update of the older ARRESTOR code, could be considered as part of any new approval process. Although based on anecdotal experience, the researchers have noted a seeming lack of awareness regarding the exis- tence, usage, and function of EMAS among airline pilots. This lack of awareness has been observed in both newer and sea- soned pilots. It is unclear whether awareness is greater among pilots that typically land at airports with EMAS. Unfortu- nately, response from the pilot community was limited dur- ing the survey process. Nevertheless, it may be beneficial to consider pursuit of an educational effort to increase aware- ness of the existence and function of EMAS within the pilot community. C H A P T E R 1 5 Conclusions

15.2. Experimentation Phase The experimentation phase of the effort involved an exten- sive evaluation of four arrestor candidates: 1. Glass foam arrestor (passive) 2. Aggregate foam arrestor (passive) 3. Engineered aggregate arrestor (passive) 4. Main-gear engagement active arrestor (active) A combined modeling and simulation effort successfully replicated each candidate in order to evaluate its merit and compare it with the existing EMAS performance. 15.2.1. Passive System Evaluation Chapter 9 through Chapter 11 gave specific recommenda- tions and guidance for transitioning the three passive candi- dates into fielded systems. The findings of this research indicate that a fieldable system is feasible for all three candidates. The aggregate foam concept offers superior multi-aircraft performance due to its depth-varying material properties. This multi-aircraft performance is arguably the most important fac- tor for keeping arrestor beds short, reducing land requirements, and increasing the rated aircraft exit speeds. Additionally, it provides a substantially lower estimated cost per square foot. However, because the aggregate foam concept uses a novel crushable material and cover layer, the number of unknowns is greater. The arrestor materials require additional evaluation in order to produce high-confidence performance estimations. Overall, the combination of unknown factors and anticipated cost and performance improvements make it a moderate-risk/ high-payoff concept. Conversely, the glass foam concept is the most conserva- tive of the three alternatives in terms of development risk and payoff. Glass foam provides an alternative to the current EMAS technology with promising improvements regarding service life and maintenance, but at equivalent cost and performance. The mechanics of the material are predictable with relatively few unknown factors. Fielding such a system would be more straightforward than with aggregate foam, and the approval process could arguably follow the shorter “equivalent” path (Section 6.3). Overall, the combination of unknown factors and anticipated cost and performance improvements make it a low-risk/moderate-payoff concept. Finally, the engineered aggregate concept provides a fea- sible alternative, but one without a particular distinguish- ing advantage. It provides cost savings and increased material durability over the current EMAS technology. However, the speed-dependent arrestor performance generally requires longer arrestor beds and diminishes the multi-aircraft per- formance. As with the aggregate foam, the materials to be used will require additional characterization in order to make high- confidence performance estimations. Overall, the combination of unknown factors and anticipated cost and performance improvements make it a moderate-risk/low-payoff concept. The selection of one or more of these alternatives for field- ing and approval is a task that requires consideration by the relevant stakeholders, which includes the government, airport community and manufacturers. Each candidate offers differ- ent advantages, risk levels, and payoff potential. Depending on the development track that is pursued, manufacturer invest- ment may be required. The extensiveness of subsequent devel- opment plans and the associated costs may determine the feasibility of such participation. As a precursor to any such development, it is recommended that the concepts for pur- suit be determined and that the relevant manufacturers be contacted for preliminary discussions of development scope and participation. New arrestor and cover-layer materials will be used for any candidate that is pursued. It would be advisable to pursue full-scale tests for these alternatives, which would allow: • Assurance of performance and safety, • Characterization of the full arrestor layups, • Down-selection of final cover layer alternatives, and • Model calibration to match final configuration performance. As part of future research, it would be advisable to test cellu- lar cement specimens and incorporate a cellular cement arrestor into the APC. Inclusion of cellular cement was omitted during the current research. However, such a model could be devel- oped in approximate form by testing a generic cellular cement material of nominally the same density. The incorporation of a cellular cement option in the APC would help to establish equivalency of various systems and provide additional com- parison of performance between the arrestor options. 15.2.2. Active System Evaluation The main-gear engagement active system candidate is not recommended for additional pursuit. While stopping the air- craft proved mechanically feasible, engaging the main-gear struts involved multiple complexities, including damage to landing gear features, damage to landing gear bay doors, and timing and deployment complexity. Additionally, some air- craft geometries made capture infeasible altogether. Nevertheless, active systems remain feasible if barrier nets are used for engagement. Using the suggested sensor and activation methods, an automated system could be developed that would eliminate the need for manual triggering, but permit pilot over- rides. The active system approach offers the highest theoretical deceleration limits, which could produce substantially shorter arrestment distances than any passive system alternative. 156

The survey findings indicate that endeavors to implement an active civil aircraft arresting system would meet with resistance by the aviation community. If pursued, it is recommended that an educational component be included to increase awareness and reduce misconceptions regarding such systems. 15.3. Final Conclusions The research effort achieved its stated objective, which was to advance the development of alternative civil aircraft arrest- ing systems. The research evaluated four alternatives to the current cellular cement EMAS technology, and successfully identified options that can provide improved performance, lower cost, and/or higher durability. Pursuing full development and testing of one or more of these candidate systems would be the next step toward obtain- ing requisite FAA approval. Once fielded, the new arrestor sys- tem would provide additional options to airport operators for achieving RSA compliance. Increasing the choices avail- able would allow decision makers to select the arrestor option that best fits with the budgetary, climate, and space constraints of the facility. 157

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TRB’s Airport Cooperative Research Program (ACRP) Report 29: Developing Improved Civil Aircraft Arresting Systems explores alternative materials that could be used for an engineered material arresting system (EMAS), as well as potential active arrestor designs for civil aircraft applications. The report examines cellular glass foam, aggregate foam, engineered aggregate, and a main-gear engagement active arrestor system.

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