National Academies Press: OpenBook

Developing Improved Civil Aircraft Arresting Systems (2009)

Chapter: Chapter 2 - Literature Review

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Page 22
Suggested Citation:"Chapter 2 - Literature Review." 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 23
Suggested Citation:"Chapter 2 - Literature Review." 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 23
Page 24
Suggested Citation:"Chapter 2 - Literature Review." 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 24

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22 2.1. General The literature review began with research into past arrestor system development and current arrestor requirements by the FAA. This research identified a number of technical areas of interest, which then turned into second- and third-stage literature research. Altogether, over 130 references were collected and reviewed on a spectrum of topics pertinent to arrestor systems. A summary of important information gleaned from this research is given in this section; the annotated bibliography (Appendix A) contains a more complete listing of documents. Table 2-1 summarizes the scope of the literature review. 2.2. Historical Aircraft Arrestor Research and Development Substantial historical work has been done in the area of arrestor system development. FAA and industry documenta- tion was reviewed, sometimes requiring retrieval in hard-copy form due to the age of the material. Civil arrestor research in the 1980s examined the usage of materials such as clay, sand, gravel, water, and foam to develop a “soft ground” arrestor, as discussed by Cook (2). These materials are passive in nature, with no moving parts. The arrestment of the aircraft is accomplished by these materials as they impart a drag load on the landing gear, absorbing kinetic energy and bringing the aircraft to a stop. Cook dis- cusses how materials such as clay, sand, and water were not appropriate for various reasons. For sand and clay materials, the mechanical behavior could not be consistently predicted due to sensitivity to moisture content. Water could be shown to perform well mechanically, but only at speeds less than 50 knots, with the additional disadvantages of attracting waterfowl and freezing in cold climates. Subsequent research was undertaken to examine different variants of foam arrestor (3), from which it was determined that a cementitious foam provided advantages over polymer foams. Gravel spray caused by the aircraft tire was identified as a potential engine inges- tion hazard. Additional, limited documentation was reviewed for gravel arresting system research undertaken in the United Kingdom (UK) (4). The emphasis on development shifted, taking a direction that focused on crushable materials such as phenolic foam and cellular cement (sometimes referred to as aerated/foamed cement/concrete). White and Agrawal (5) outline that the advantage of the crushable foam materials is predictability of the drag load imparted on the landing gear and constant mechani- cal properties over a broad temperature range. Cellular cement eventually became the material of choice due to its near-zero rebound after crushing and chemically inert composition. Computer modeling and simulation have played a substan- tial role throughout the development of these passive arresting technologies. Initially, predictive codes had been developed for the modeling of taxi, takeoff, and landing on soil landing strips (6). These methods were adapted to the soft-ground arresting concept to evaluate different materials. Landing gear loads for the main and nose gear struts have been a historical area of scrutiny (2). Loadings to the nose gear in particular were noted, since materials like gravel could jeopardize the integrity of the gear and cause potential collapse. One military code, FITER1, was adapted for civil arresting applications and called “ARRESTOR,” documented by Cook et al. (7). It featured three aircraft (B707, B727, and B747) and could be used to model different foam arresting bed geome- tries. Heymsfield et al. (8) have recently used the ARRESTOR code to perform sensitivity analyses on various parameters. This program has presently been superseded in capability by a proprietary predictive code used by the EMAS manufac- turer, ESCO. Active arresting systems that use military-type friction brakes (BAK-12, etc.) have been adapted to civilian aircraft in the past. Documentation in our research has been sparse on this subject, however, and the majority of knowledge gained on the sub- ject has been through discussions with ESCO and by reviewing C H A P T E R 2 Literature Review

a number of their product brochures. Active arresting systems have seen the most widespread use for military aircraft with tail hooks. To arrest civilian aircraft, netting systems are used to either wrap over the aircraft wings or engage the main landing gear struts. The former approach presents hazards for occupant emergency egress from the aircraft, as the netting can block exit hatches. The latter approach has technical dif- ficulties due to widely varying landing gear geometries. 2.3. Recent Arrestor Research Due to some of the present concerns regarding the life-cycle performance of the arrestors, Minneapolis–St. Paul Airport (MSP) has conducted several limited research and testing efforts. Stouffer (9) performed in-situ environmental tests on the arrestor bed and found a high relative humidity inside the bed, indicating the trapping of moisture inside the blocks. Stehly (10) conducted testing on some older blocks of the MSP 12R/30L arrestor, including fire-truck overruns and rough in-situ compression tests. Both tests indicated that performance degradation had occurred since the 1999 installation. Design reports for arrestor beds were reviewed (11), as well as relevant excerpts from airport certification manuals (12). The design reports indicate that, in actual practice, the exit-speed performance of a given arrestor bed can vary widely across the aircraft fleet; some aircraft will be arrested at higher speeds than others. Some literature was found pertaining to gravel truck arresting systems, typically used for arresting runaway trucks on downhill roadways. Rogers (13) discusses cold-weather testing information that demonstrates the potential for aggre- gate arresting beds to freeze over and become ineffective in harsh winter environments. 2.4. Landing Gear and Aircraft Dynamics Landing gear was studied by the project team following the review of soft-ground arrestors. A key performance metric for soft-ground arresting systems is the consistency and pre- dictability of the loads imparted to the landing gear: loadings that are too high can damage or fail the gear, and loadings that are too low will not efficiently arrest the aircraft. Accurate prediction of these loads cannot be obtained without also capturing the dynamic response of the aircraft and landing gear. Much like driving a car over speed bumps, the suspension response can dictate the overall degree of bounce and sub- sequent pitching, or “porpoising,” that occurs. Inconsistent materials can lead to more porpoising, and hence higher loads on the landing gear. While many documents have been reviewed, a few will be singled out here. Currey (14) provides a general text describing the fundamentals of design and analysis of landing gear, allow- ing for the general sizing of struts, tires, etc. Pritchard’s (15) overview of landing gear dynamics provides a substantial array of simulation options, which will be employed in the second phase of the effort. Chester (16) outlines a modeling approach for a generalized aircraft of varying size, with a focus on land- ing gear dynamics and overall airframe response. Altogether, we find that relevant variables to the current problem include strut stiffness and stroke length, tire pressure and dimensions, aircraft mass and moments of inertia, etc. Since these proper- ties for an actual aircraft are proprietary manufacturer infor- mation, the information from these references will prove beneficial for approximation. Experimental studies undertaken by the FAA have been reviewed. Micklos and DeFiore (17) discuss video analysis techniques for determining aircraft parameters based on obser- vations of aircraft landings. Tipps et al. (18) describe landing gear load factor statistical studies based on in-service aircraft measurements. These and similar reports focus on determining the level of loading that in-service aircraft actually experience, often with a focus toward determining the appropriateness of the current Federal Aviation Regulations (FAR) requirements. As such, they have less relevance to the current effort, where load limits for aircraft are the focus. 2.5. Airport Operations In order to understand the implications of arrestor design on airport operations, several sections of CFR Part 14 were reviewed (19, 20). FAA Order 5200.8 outlines the Runway Safety Area Pro- gram (21). The intent of the program is to ensure that all Part 139 airports in the United States are brought into compliance with RSA requirements. Historical data shows that most overruns take place at speeds of 70 knots or less, and that aircraft typically come to rest within 1,000 ft of the end of the runway (Section 4.4.1). Consequently, a standard RSA has a typical length of 1,000 ft. For airports not in compliance, five remedial measures are described: relocating runways, reducing runway length, a combination approach, the use of declared 23 Document Type Topical Areas Government research Government regulations Journal papers Patents Manufacturer specifications and research Reference books Magazine/newspaper/Internet articles Arrestor systems Aircraft and landing gear dynamics Airport operations Modeling and simulation Material science Table 2-1. Literature review summary.

distances, or the installation of an EMAS. From an operations standpoint, any arrestor developed must accomplish the goal specified by the EMAS advisory circular: to arrest aircraft with an exit speed of 70 knots, thereby providing protection that is equivalent to a standard RSA (1). The current status of the Part 139 airports is summarized in an FAA database (22), which was consulted for determining the survey participant pool. 2.6. Accidents and Incidents Two major studies have documented historical overrun accidents and incidents. In 1990, David (23) conducted an extensive review of overruns and summarized historical event data, including the distance travelled and the final location of the aircraft with respect to the runway end and center- line. DOT/FAA/CT 93-80 (5, p. 1) gives a histogram sum- marizing the exit speed distribution. This plot produced the historical basis for associating an exit speed of 70 knots or less with capturing roughly 90% of overruns. The arrestors have historically used 70 knots as a design objective for this reason. In 2007, Hall et al. (24) revisited the topic with a study for TRB/ACRP. This research involved newer data compiled from several database sources pertaining to landing overruns, landing undershoots, and takeoff overruns. The database compiled in that study was obtained and reviewed, and served as a sub- sequent basis for the risk assessment of this effort. The 90% exit speed appears to have shifted since the previous research, and per the current data, it appears that the threshold could now be higher than 70 knots (Chapter 5). AC 150/5200-37 presents guidance on safety manage- ment systems (SMS) and includes relevant risk assessment approaches (25). It has become apparent through the literature review that the reliability and risk for passive arrestors is less understood than for military-type systems. The military sys- tems have been well characterized and are required to pass a 97.5% reliability criterion; no parallel currently exists for civil systems. The SMS guidance presents a paradigm to be adopted with civil arresting systems. National Transportation Safety Board (NTSB) incident reports for several overruns were reviewed, including some involving arrestor beds (26–28). These documents provide some information in terms of exit speed and distance travelled through the arrestor beds. However, detailed information regarding the loading and deceleration effected by the arrestors is not provided. 2.7. Financial FAA Order 5200.9 provided guidelines for estimating the costs to establish an EMAS at an airport (29). It provided a process for estimating the life-cycle costs of a system and estab- lished guidelines for comparing that cost to maximum feasible thresholds. The data contained therein served as a baseline for comparison with the airport operator survey (Chapter 3). 2.8. Patents Various patents, dated from 1962 to the present, were iden- tified pertaining to aircraft arrestor concepts. These patents are given in the annotated bibliography (Appendix A). 24

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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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