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55 hobbyists. Private airports and heliports are built and used at any time in favor of the anytime, anywhere concept, either in many cases by business and public-use operators such to disperse evacuees or to concentrate delivery of supplies as EMS. Military airfields are mentioned for their obvi- and relief workers. ous function and because they can serve as medical evac- Commercial air operations are tightly managed and con- uation destinations (particularly for quarantine purposes). trolled (by the ATC system and company dispatch offices). Communications and Navigation--Communications fa- The result is a system that can respond immediately to criti- cilities, both public and private, are the backbone of avi- cal stimuli. Planning and control are critically important in ation. Communications are essential in both controlled the evacuation mode. Air operations (unlike automobile and uncontrolled environments. In contrast to most other evacuation) require staging of empty aircraft into the region forms of transportation, the robust aircraft communica- to be evacuated. Unlike ground environments, where inbound tions environment (which is immune to short-term lanes can be switched to double outbound capacity, the de- power failures) allows rapid response to changing con- parture capacity of an airport cannot typically be increased. ditions and emergencies (witness the rapid grounding of Weather disruptions to air travel result from major storm the entire commercial air fleet on September 11, 2001). systems redirecting en route progress and slowing or prevent- This capability can serve to eliminate general (or non- ing operations to major airports. Such a situation can diminish specific) threats, avoid regional threats, or respond to the ability of aircraft to respond to emergency situations. These supply or evacuation requests. The navigation and land- situations serve as valuable models for studying the effects of ing system (much of which is also immune to power out- attacks that result in closure of one or more airports. ages) is used by virtually all operators, even visual flight The airline and airport infrastructure is sufficiently robust rules (VFR) operators. Operations by instrument flight to supply fuel and flight crews for intensive relief operations rules (IFR) operators can continue in low-visibility con- over an extended period of time (possibly 2 weeks) without ditions regardless of the cause of the reduced visibility. re-supply. General aviation airports also typically store sub- Air Traffic Control (ATC)--The ATC system, operated stantial quantities of fuel relative to the size of their operation. exclusively by the federal government (and military), With respect to industry management, the pyramidal struc- guarantees separation of IFR aircraft from other aircraft ture of the ATC system and its independent power supplies and facilitates separation of almost all aircraft. It pro- and communications channels, the highly-organized nature vides the planning and sequencing services that ensure of airline (and corporate) flight dispatch offices, and the the efficient overall operation of the system. The ATC ARINC communications network provide for a very highly system is fundamentally configured as a pyramid. The structured management and control system. Each aircraft is System Command Center at the top originates the basic capable of virtually autonomous operation even in low visi- strategy to control flow and to minimize delays and bility conditions (assuming that the GPS network is opera- weather impacts. The twenty Air Route Traffic Control tional, although it is substantially true even if GPS is not Centers (ARTCCs) in the middle control the en route operational). All that is required from the ground environ- operation of aircraft and ingress/egress to uncontrolled ment are separation services. Tight control over aircraft airfields. Finally, the many Terminal Radar Control operations enables them to respond as directed. (TRACON) Facilities, control towers, and flight service stations at the bottom control landings and takeoffs and 3.4.7 Emergency Plans and Organization handle flight plan filings. Capabilities and Limitations of Air Transportation 3.4.6 Operations A very important capability lies in the use of helicopters to provide first-responder and evacuation services and sur- A fundamental characteristic of the air transportation in- veillance of a disaster scene to coordinate activities of ground dustry is that, with the exception of medical evacuation, air personnel. The limitations are that only a few such heli- transportation is always multi-modal. This applies to cargo copters are properly equipped and staffed in any given area, as well as people (and contrasts with automobile and truck severely limiting the scale of services that can be provided. transportation, which is unimodal). Inasmuch as most of the population of the United States lies Private users of aviation operate in an "anytime, any- reasonably close to the oceans and inland seaways patrolled where" environment and typically fly as directly as possible by the USCG, the USCG helicopter fleet, fundamentally from origin to destination. The air carrier system has evolved designed for search and rescue operations, is a significant to what is known as the "hub and spoke" system, with each adjunct to local capabilities. National Guard and Army heli- airline concentrating operations at one or more hub airports. copters are important for evacuation operations. This is extremely important from the threat viewpoint. A serious limitation on the ability to respond in a local dis- The hub can be used to disperse contaminants widely via the aster environment stems from the fragmented jurisdictions of spokes. It, however, has little effect on air transport in the the various involved organizations. Even local law enforce- emergency response mode. Hub and spoke can be abandoned ment agencies in many metropolitan areas are not able to