National Academies Press: OpenBook

Developing Improved Civil Aircraft Arresting Systems (2009)

Chapter: Chapter 4 - Review and Documentation of FAA Parameters

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Suggested Citation:"Chapter 4 - Review and Documentation of FAA Parameters." 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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Suggested Citation:"Chapter 4 - Review and Documentation of FAA Parameters." 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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Suggested Citation:"Chapter 4 - Review and Documentation of FAA Parameters." 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 37
Suggested Citation:"Chapter 4 - Review and Documentation of FAA Parameters." National Academies of Sciences, Engineering, and Medicine. 2009. Developing Improved Civil Aircraft Arresting Systems. Washington, DC: The National Academies Press. doi: 10.17226/14340.
×
Page 37
Page 38
Suggested Citation:"Chapter 4 - Review and Documentation of FAA Parameters." 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 38

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34 4.1. Relevant Literature Of the documents reviewed, those most relevant to deter- mining the basis of FAA parameters governing the arrest of civil aircraft are as follows: AC 150/5220-9a. Aircraft Arresting Systems on Civil Airports. FAA, 2006. AC 150/5220-22a. Engineered Materials Arresting Systems (EMAS) for Aircraft Overruns. FAA, 2005. Order 5200.9. Financial Feasibility and Equivalency of Runway Safety Area Improvements and Engineered Material Arresting Systems. FAA, 2004. Order 5200.8. Runway Safety Area Program. FAA, 1999. Runway Safety Area Status Database. FAA, 2007. 4.2. Parameter Diagram Figure 4-1 illustrates the FAA parameters governing civil aircraft arrestors. Parameters specifically cited in the EMAS advisory circular (or elsewhere) are shown with underscores. At the most general level, the parameters were categorized as either inputs or outputs. Many of the inputs listed are essentially requirements, and these requirements can apply to the initial or final conditions of an arresting event. The man- ner in which the FAA drafts its requirements will govern the outputs: arrestor cost, size, performance, and so on. As such, one could summarize by saying that the inputs are requirements and the outputs are consequences of the requirements. Changes in the requirements will have an impact on system cost, the manner of the arrestor function, and so on. 4.3. Parameter Relationships Figure 4-2 illustrates a detailed version of the prior param- eter diagram, showing the relationships from a standpoint of designing and installing an arrestor. The performance requirements, as set forward by the FAA, combined with the site constraints, would drive the selection of an appropriate arrestor type for the facility. For civil applications, there is currently only one EMAS option; however, this could broaden upon approval of other alternatives. Given the performance requirements of the standards and the site constraints, the specific arrestor design for the facility would be determined. This final system design determines the cost for the system installation. The arrestor type determines the nature of the maintenance and repairs required, directly affecting those cost components. The arrestor type also has the most substantial impact on the installation time, service life, and downtime during repairs. The particular specifications of the installed system do not have a great effect on the time components. From a regulatory standpoint, the performance requirements put forward by the FAA regarding exit speeds and the post- event aircraft condition (permissible level of damage) have the most tangible impact on system cost. While other factors may affect cost as well, the connectivity is more difficult to quantify. Chapter 5 demonstrates the cost impact of these parameters. Figure 4-3 illustrates the parameter relationships for an overrun event. Within this context, design considerations are no longer relevant. The diagram assumes that all design deci- sions were previously made and that an arrestor system has been installed at the facility. During an arresting event, the initial conditions (upper left) of the aircraft type, exit speed, etc., interact with the arrestor system to produce a performance output. The arrestor trans- lates the overrun conditions into deceleration loads on the plane, an overall stopping distance, etc. The arrestor type and specifications will impact the performance significantly. As the research later shows, dif- ferent arrestor types have different inherent performance capabilities. C H A P T E R 4 Review and Documentation of FAA Parameters

4.4. Critical Parameters 4.4.1. Exit Speed FAA AC 150/5220-22A requires that an EMAS have a stan- dard design exit speed of 70 knots and a minimum of 40 knots (1). The 70-knot standard is intended to enable arrest of 90% of overruns. The 40-knot minimum is provided as an excep- tion for airports with highly constrained RSAs. A review of the overrun data collected in subsequent ACRP research (24) indicated that the 70-knot requirement may no longer be sufficient to reach the intended 90% arrest rate (Chapter 5). 4.4.2. Damage to Aircraft FAA AC 150/5220-22A requires that the arrestor not struc- turally damage the aircraft. However, this requirement could potentially be revised to permit a degree of flexibility in the interests of reducing overall risk. More aggressive decelerations would be possible if the designs were permitted to overload/collapse the nose gear, as long as the main gear remained intact. While this certainly results in a monetary impact with regard to aircraft damage, prior EMAS testing suggests that it may pose minimal hazards to aircraft occupants in some cases. In the event of a nose gear collapse, some aircraft would be more adversely affected than others would. Aircraft with low-slung engines could poten- tially undergo engine damage and/or ingest arrestor material; the risks of these effects have not been quantified. Additional concerns would apply to turbo-prop aircraft, where propeller damage could present additional hazards. As an example of potential implementation, if a plane continues to penetrate beyond 75% of an arrestor bed’s length, it could enter an “all or nothing” zone, in which the resistance of the bed increases in a final attempt to arrest the aircraft. Nose gear collapse could be preferable to the consequences of failing to stop the aircraft, depending on what hazards lie beyond the arrestor bed. A robust approach could consider an overall risk assess- ment, as the consequences of an un-averted overrun will not be equal for all facilities. It is suggested that the requirements 35 Initial Conditions • Aircraft Type • Exit Speed • Runway Conditions • Etc. Performance Requirements • Aircraft Condition • Occupant Survival • Occupant Egress • Reliability • Exit Speed Rating Airport Constraints • RSA Dimensions • Runway Dimensions Other Requirements • Life-Cycle • Maintenance Access • Emergency Vehicle Access • Reliability Arrestor Type • Current EMAS • Active System • Other Passive System Arrestor Performance • Deceleration • Landing Gear Loads • Aircraft Controllability • Required Distance • Multi-Aircraft/Fleet Performance Cost • Site Preparation • Installation • Maintenance • Repair After Overrun • Replacement Time • Installation • Repair • Service Life Inputs/Requirements Outputs/Consequences Installed Arrestor • Type • Size/Dimensions • Other Specifications Figure 4-1. Diagram of FAA parameters.

concerning landing gear loading be revisited in order to deter- mine if case-by-case exceptions may be permissible. 4.4.3. Collateral Damage To date, there has been minimal discussion in FAA liter- ature about assessing collateral damage in the event of an aircraft overrun. As a resource for future consideration, aircraft damage and occupant injury have been included in the risk analysis software developed in recent ACRP research (24). For airports with highly constrained RSAs, it may be advisable to include a metric for collateral damage. FAA AC 150/5200-37 (25) provides a basic framework for risk-oriented planning. 4.4.4. Occupant Injury A document found during the literature review indicated that arrestments should be limited to under 1 g, based on occupant injury criteria (31). Several individuals from the FAA stated that a 1 g limit might stem from FAR landing gear load- ing criteria, but that they were not aware of any such injury criterion. This topic was investigated further by enlisting a human injury expert. The subsequent research indicated that the deceleration injury threshold is substantially higher than 1 g. The conclusion, in the absence of other evidence, is that the 1 g deceleration limit mentioned in the reference previously cited was likely errant. Details regarding the human injury analysis are given in Appendix E. 4.4.5. Deceleration Thresholds Table 4-1 summarizes deceleration thresholds for aircraft damage and occupant injury. For the nose gear criterion, the 0.23 g deceleration assumes that no rearward loading is applied to any other part of the aircraft (main gear, thrust reversers, etc.). For the main-gear deceleration of 1.13 g, a similar assumption has been made. Both 36 Initial Conditions • Aircraft Type • Exit Speed • Runway Conditions • Etc. Performance Requirements • Aircraft Condition • Occupant Survival • Occupant Egress • Reliability • Exit Speed Rating Airport Constraints • RSA Dimensions • Runway Dimensions Other Requirements • Life-Cycle • Maintenance Access • Emergency Vehicle Access • Reliability Arrestor Type • Current EMAS • Active System • Other Passive System Arrestor Performance • Deceleration • Landing Gear Loads • Aircraft Controllability • Required Distance • Multi-Aircraft/Fleet Performance Cost • Site Preparation • Installation • Maintenance • Repair After Overrun • Replacement Time • Installation • Repair • Service Life Inputs/Requirements Outputs/Consequences Installed Arrestor • Type • Size/Dimensions • Other Specifications Figure 4-2. Diagram of FAA parameters: detail for system design and installation.

37 Initial Conditions • Aircraft Type • Exit Speed • Runway Conditions • Etc. Performance Requirements • Aircraft Condition • Occupant Survival • Occupant Egress • Reliability • Exit Speed Rating Airport Constraints • RSA Dimensions • Runway Dimensions Other Requirements • Life-Cycle • Maintenance Access • Emergency Vehicle Access • Reliability Arrestor Type • Current EMAS • Active System • Other Passive System Arrestor Performance • Deceleration • Landing Gear Loads • Aircraft Controllability • Required Distance • Multi-Aircraft/Fleet Performance Cost • Site Preparation • Installation • Maintenance • Repair After Overrun • Replacement Time • Installation • Repair • Service Life Inputs/Requirements Outputs/Consequences Installed Arrestor • Type • Size/Dimensions • Other Specifications Figure 4-3. Diagram of FAA parameters: detail for arresting event performance. Event/Criteria Deceleration Nose Gear Rearward Failure 0.23 g Main-Gear Rearward Failure 1.13 g Combined Main- and Nose-Gear Rearward Failure 1.36 g Long duration (typical arrest) 4.00 g Traumatic Brain Injury (TBI) Threshold Short duration (<1 sec) 9.00 g Typical EMAS Deceleration (Section 5.2.1) ~ 0.35 to 0.85 g Table 4-1. Deceleration thresholds for aircraft damage and occupant injury.

of these values represent cases that, in practice, are probably unattainable. Surface-based arrestors will apply a deceleration load to the main and nose gear struts simultaneously. As such, the combined main and nose gear deceleration of 1.36 g is the most useful landing gear metric. It represents the theoretical limit for aircraft deceleration that could be obtained by perfectly distributed loading of the main and nose gear struts, such that all struts were at their maximal loading thresholds simultaneously. While not realistically attainable, the 1.36 g deceleration would represent the ideal case. The long-duration traumatic brain injury (TBI) thresh- old is most appropriate for application to typical aircraft arrests, which would last for several seconds. For short- duration pulsed loads, the 9 g limit could be assumed instead. Details regarding the human injury analysis are given in Appendix E. Given the deceleration thresholds indicated, the aircraft limit loads would constrain the arrestment rate, rather than occupant injury criteria. The landing gear loads have been the historical limitation for EMAS designs. The nose and main gear are not loaded in an ideal fashion, with the nose gear load generally limiting the obtainable decelerations to 0.35 to 0.85 g. Perhaps the only realistic way in which to obtain higher decelerations for an aircraft is via an active arrestor system, using either cables or barrier nets to engage the aircraft. Such systems would open the possibility of exceeding the 1.36 g limitation, at which point the 4 g TBI criterion would become the performance constraint. Obviously, arrestment distances could be reduced significantly. Offsetting this advantage, air- frame damage could result from such loads on the aircraft. Assessing the potential impact to the aircraft was beyond the research scope. 38

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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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