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Many people, including licensed pilots, are surprised to learn that many airports in the US with no radar coverage or control tower have instrument approach procedures with final approach segments in uncontrolled (class G) airspace, where the pilot, not the controller, is responsible for traffic avoidance.  Since the floor of controlled airspace near instrument airports in the US is typically only 700’ AGL, ATC can provide adequate separation between IFR arrivals and departures, but the possibility exists that VFR traffic of which ATC has no knowledge may be present in the airport vicinity below 700’.  Regulations permit VFR flight within class G airspace in the vicinity of an airport as long as the aircraft can remain clear of clouds and maintain flight visibility of 1 mile.  Because there is no practical way for an arriving IFR aircraft to see-and-avoid VFR traffic operating near the base of a 700’ ceiling, the only means for ensuring separation between IFR and VFR traffic in these circumstances is mutual use of the Common Traffic Advisory Frequency for position reporting.  If the VFR aircraft is not radio-equipped, separation is simply left to chance.  Fortunately, the low volume of VFR operations at airports in extremely marginal meteorological conditions has made traffic conflicts of this type rare.
1.2 Automated Instrument Procedures

There have been a number of studies aimed at developing efficient instrument access to non-radar facilities through the automation of approach and departure traffic separation procedures.  Most of these attempts depend on 4-D (lateral, vertical and time determinate) flight path prediction. Tobias and Scoggins3 attempted to automate traditional IFR services by building off Tobias’ earlier work,4 describing prediction of conflict-free approach paths.  Using conventional separation standards, they generated airport-relative altitude, azimuth and range data from the beacon transponder systems (Mode A/C).  From these data, the ground-based automation assigned routes of flight designed to provide sequence and maintain separation.  A synthesized voice system transmitted these clearances to the participatory aircraft via VHF radio.  Morgenstern and Telsch5 described a similar system intended for VFR advisories.
The most significant obstacle to deploying such a full-scale automated approach and departure system is the challenge of legally certifying it. The air traffic control system is an inherently conservative institution: even incremental changes to ATC procedures require lengthy regulatory processes.  Moreover, the system has evolved though many hundreds of thousands of hours of service in all kinds of conditions, and represents the distillation of often bitter experience with a myriad operational difficulties and mishaps.  The safety record of the modern ATC system is exemplary, and the procedures upon which this record is based should not be altered lightly.  With this in mind, we propose a much less ambitious approach/departure automation system than has heretofore been advanced: one that is based on the existing, well-proven non-radar “one-in/one-out” IFR procedures described in Section 1.1.  While this method is neither the most efficient use of the airspace, nor the most convenient for the pilot, it does have the virtues of safety, simplicity and relatively low cost.  While our proposed system is limited to relatively low-density operations, it represents architecture from which more efficient, albeit more complex, full-service automated systems can be developed after operational experience has been accumulated and as demand for point-to-point operations increases.
　
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本文鏈接地址：A METHOD OF SEPARATION ASSURANCE FOR INSTRUMENT FLIGHT PROCE(3)