Because newly introduced procedures must function within the existing National Airspace System (NAS), their architecture must complement, and to the largest extent possible, make use of existing infrastructure and procedures. Before addressing proposals for automation of non-radar approach and departure separation services, we will review these existing procedures.
Separation services can be classified as either radar (target-to-target) or procedural (target-to-airspace). The latter is used when accurate surveillance data is not available, (generally non-radar environments), or the intent of a target is unknown (VFR targets or IFR operations in uncontrolled airspace). There are also hybrid techniques, utilizing both local target separation and more general airspace structure to keep non-participatory aircraft separated from IFR operations. One example is a block of high altitude airspace, known as a “wave window”, that allows gliders not equipped with transponders to operate in Class A Positive Control Airspace. All IFR traffic is separated from the block of airspace, and within the window, the gliders use a combination of see and avoid and specialized rules of the road to maintain their own separation from each other. ATC is responsible for the former, the pilots the latter. Similarly, the structure of ICAO-defined airspace types serves a similar purpose: to minimize the mixing of different types of traffic where possible, and ensuring the compatibility of mixed traffic by mandating equipment appropriate to each type of airspace.
In a non-radar airport environment, separation services are often provided to IFR flights by ensuring that airspace around the airport has no other IFR flights within it, i.e. the airspace is “sterile”. Additional requests for operations at the airport are postponed until the IFR arrival or departure is complete, hence the name “one-in/one-out”. For departures, pilots are restricted to a specified departure window known as a clearance void time, during which the airspace from the departure airport to the point at which radar contact is expected or position reporting will commence is guaranteed by ATC to be sterile. If the departure window is missed, a new clearance request must be made to gain entry to controlled airspace. For arrivals, the same principles apply, though the “one-in/one-out” window is typically defined by the loss of radar contact (common in descent) and the pilot’s action of closing their flight plan. If, for example, an arriving aircraft requests an approach while another aircraft was landing, the arriving aircraft will likely be required to hold at a location at a safe distance and altitude from the active approach path. They will be given an Expect Further Clearance (EFC) time when they can expect to receive clearance to initiate their approach. This procedure permits ATC to separate multiple flights in the absence of surveillance data (radar) without requiring excessive position reporting.
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本文链接地址：A METHOD OF SEPARATION ASSURANCE FOR INSTRUMENT FLIGHT PROCE(2)
