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important distinction between U.S. practice and that of many other countries is the use in
visual meteorological conditions (VMC) of visual final approaches when the initial
approach is in instrument meteorological conditions (IMC). This yields a major capacity
benefit.
In its 1988 paper, quoted above, the AACC noted, “...the contrast between the spacings
allowed under current U.S. procedures, and the efforts under way to improve on them;
and the standards in other parts of the world. Since each of the current U.S. minimums
was adopted after lengthy study and testing/demonstration, the data have been available to
all, and the safety record achieved with the U.S. standards, in some cases over many years
of use, has been superb, they should surely receive sympathetic consideration by ICAO as
well.”
A successful approach has been used by the FAA (starting in the 1970s) for examining the
possibility of reducing separation standards for parallel runways having independent IFR
operations. Extensive demonstrations, tests, and consultations among concerned parties
and operations experts led to a reduction in the minimum allowable separation between
parallel runways. The required spacing has now reached 3,400 ft.
Other factors may affect the safety and acceptability of allowing simultaneous independent
approaches to more closely separated parallel runways during IMC:
· More automation in flight control systems that reduce the amount of air space
occupied and the impact of missed approaches,
SEPARATION SAFETY MODELING
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· Automatic warnings of aircraft deviations from assigned paths provided by the
ground data acquisition sensor, and
· Special training for pilots who will be making simultaneous approaches.
The introduction of automatic dependent surveillance (ADS) adds a new possibility for
reduced separation minima. The accuracy of the system is prospectively very high (100
meters) if Global Positioning System/Global Navigation Satellite System (GPS/GNSS) is
used. While the use of satellite navigation may reduce exposure to blunders, the system is
“dependent” on aircraft information - it incorporates no independent (terrestrially-based)
verification of aircraft position. Where no secondary navigation (e.g., inertial) or
surveillance systems are available, failure of the ADS aircraft equipment or the satellite
service will eliminate both navigation and surveillance services for all en route aircraft with
potentially catastrophic results.
2.2 THE SEPARATION STANDARD ESTABLISHMENT PROCESS
2.2.1 The FAA Separation Standard Establishment Process
Although the FAA Flight Standards Service and the FAA Office of Air Traffic must jointly
approve any changes in separation standards in the U.S. National Airspace System (NAS),
there apparently is no formal certification and approval process for making such changes.
The (informal) process normally begins as the result of a concern: capacity limitations,
safety (e.g., Boeing 757 wake vortex-induced accidents), operators’ desire to fly more fuel
efficient flight paths, etc. Cost/benefit studies are performed, which may include
simulating the effects that proposed changes would have on en route and terminal airspace
and on airports. Such effects might include changes in the number of potential airspace
conflicts, an exceedence of airport capacities, and delays. Real time, human-in-the-loop
simulations may be performed to determine how pilots and controllers might react in
hazardous situations. Probabilistic analysis might also be used to estimate relative or
absolute safety levels. If the issue is one of amelioration of a hazardous safety situation,
the National Transportation Safety Board may make a non-binding recommendation.
If the issue is not in need of an immediate response and/or there are questions of
equipment specification development, the FAA will likely request that the RTCA
(formerly named the Radio Technical Commission for Aeronautics) study the question and
related proposals. The RTCA [Internet location: http://www.RTCA.org] acts as a forum
for government, manufacturer, operator, pilot, international, and other aviation community
entities, which present their views and work together to arrive at a consensus on issues.
Special Committees are often formed, with representatives of the concerned entities, to
address technical issues, including issues of proposed mandatory standards, such as
equipment carriage and specifications. Examples of such Special Committees, are the
former SC-150 on Reduced Vertical Separation in En Route Airspace, SC-147 on Traffic
Alert and Collision Avoidance (TCAS), SC-181 on Navigation Standards, and SC-184 on
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a concept paper for separation safety modeling(9)
