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43 6.1. Approval Process for New Arrestor Development The researchers engaged in discussions with both the FAA and manufacturers regarding the approval of new arrestor systems. Currently, only one EMAS system has obtained FAA approval, and new entrants to the arrestor market often cannot determine what steps to take toward gaining approval for their new designs. All parties concurred that a process is needed whereby new arrestor systems can be developed and gain FAA approval. As a starting point, the FAA has stated that the essential performance requirements contained in AC 150/5220-22a will be required for other arresting system alternatives. The FAA has determined that the Airport Engineering/Airport Safety and Standards division, AAS-100, will act as the primary point of contact for companies submitting concepts. Discussions with the FAA generated a number of ideas regarding the approval process. This report outlines a poten- tial approval process, intended as a starting point for ongoing dialogue and modification. Based on the historical development of the EMAS concept and the technical issues involved in arrestor systems, a two- branch approval process is proposed (Figure 6-1). A normal approval process would be required for arrestors substantially different from the current EMAS design. For systems that do not differ substantially, however, a shorter âequivalenceâ process is recommended. When a manufacturer submits a concept to the FAA, the first step would require identifying whether or not the system qualifies as a design equivalent to the current EMAS or constitutes a different dynamic approach. This determination will then dictate what further steps the manufacturer would need to take for approval. 6.2. Normal Approval Process The ânormalâ approval process would require the stages outlined in Figure 6-2. This process does not assume that an arrestor is passive, nor that it engages the aircraft at the tire/ground interface. The normal process is intended for application to a full spectrum of design concepts. It requires that a manufacturer undertake (1) initial data collection, (2) feasibility calculations, (3) first-principles computer modeling, and (4) small-scale testing. The results would be submitted to the FAA as an application for a Cooperative Research and Development Agreement (CRDA). The CRDA would then facilitate full-scale aircraft testing, which should be required for systems fundamentally dissimilar from the existing EMAS design. After testing, the manufacturer would be required to demonstrate the ability to predict system performance with a computer model, as applied to different sizes and types of aircraft. Finally, the manufacturer would apply for FAA approval of the system. 6.3. Equivalent Approval Process Obviously, the normal process would require substantial financial investment and involve several complex steps. For some applicants, these factors could preclude involvement, thus stalling potential improvements to the current EMAS approach. The âequivalenceâ process of Figure 6-3 allows for a simplifica- tion to the normal approach if certain conditions are met. The equivalence process would require that the new concept constitute an equivalent to the current EMAS design at a mechanical level. It is restricted to replacement materials that are laid out in a geometrically similar bed and produce a dynamically analogous load on the landing gear. An aggregate system, for example, would not constitute such an equivalent, since it has other physical mechanisms at work than a crushable foam material (Section 7.4). Meanwhile, another crushable foam could constitute such an equivalent. To date, many crush- able materials have been proposed as alternatives to cellular cement (Sections 7.3 and 7.4). The cellular cement could be replaced with a different crushable medium of similar prop- erties and still obtain analogous arresting performance. Further, the term âequivalentâ is not intended to prevent new materials from superseding cellular cement. It requires C H A P T E R 6 Approval and Commercialization Study
that the mechanical behavior be sufficiently analogous to permit the same predictive models to be employed (i.e., the ARRESTOR code, etc.). However, improvements in other areas, such as life-cycle performance, would be encouraged. To demonstrate equivalence, the manufacturer would (1) conduct thorough material testing, (2) generate feasibil- ity calculations, (3) perform small-scale tests, and (4) make the case for equivalence in report form. The FAA would then review this report and make a determination as to how compelling the data appears. 6.4. Updating of the ARRESTOR Code For the near-term development of alternative materials via the equivalent approval process, it would be necessary to have a prediction and planning program. ARRESTOR, though an old code at present, can predict arresting distances for various bed geometries. It models a general crushable foam material and permits the user to specify different compression strengths to be modeled. As such, ARRESTOR could serve the 44 Figure 6-1. Approval paths for system approval. Develop Concept Initial Data Collection & Testing ⢠Mechanical Behavior ⢠Life-Cycle Expectations Initial Feasibility Calculations ⢠Material energy capacity ⢠Estimated arrest distance ⢠Estimated deceleration Initial Modeling ⢠Numerical model (FEA, CFD, DEM, etc) of one-wheel bogey ⢠Vary speeds, tire pressure, aircraft mass, landing gear configuration Small Scale Testing ⢠One-wheel bogey tests, or equivalent if active system ⢠Sample bed cross- ection environmental test Apply for FAA Cooperative Research and Development Agreement Full Scale Testing ⢠Full-scale aircraft testing using transport-category aircraft ⢠Requires FAA cooperation Develop Predictive Model ⢠Incorporate testing and modeling data from past ⢠Validate accuracy of model FAA Approval Develop Design Program ⢠Allows planning for particular facility Figure 6-2. Proposed normal approval process for new arrestor systems in general.
up-and-coming manufacturers who do not have in-house predictive codes. ARRESTOR currently has a limited library of aircraft: the B707, 727, and 747. Only one of these aircraft is still in broad service, the B747. To act as a modern planning tool, a broader range of aircraft is needed. It is possible to accomplish this through two means. First, the aircraft manufacturers could be solicited for actual aircraft data. Second, the code could use a generalized aircraft model of arbitrary size, combined with parametric variation across a range of values. Other approaches may be possible. Alternately, a new design program could be developed. The Arrestor Prediction Code (APC) developed in the current effort (Appendix G) could serve as the basis for such a replacement. For new manufacturers to participate actively in the arrestor system market, an updated predictive code would be necessary. 45 Develop Material ⢠Depends upon material and manufacturer Material Testing ⢠Mechanical Properties ⢠Life-Cycle Properties Initial Feasibility Calculations ⢠Material energy capacity ⢠Estimated arrest distance ⢠Estimated deceleration Small Scale Testing ⢠One-wheel bogey tests ⢠Sample bed cross- ection environmental test Submit FAA Equivalence Report ⢠Present data ⢠Demonstrate EMAS equivalence FAA Approval Integrate Into Design Program (ARRESTOR) ⢠Allows planning for particular facility Figure 6-3. Proposed equivalence approval path for new crushable bed arrestor systems.