Navigation - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 211

and possible subdivisions is responsible for the control of confluenced routes in the
vicinity of the airport which covers an area, typically 50-80 km (27.0-43.2 nmi)
around the airport [ 28 ].
In addition to its basic functions, ATC may provide weather advisories, terrain
information, navigation assistance, and other services to pilots. ATC is vital for
maintaining separation between aircraft flying at high speed in congested areas and
bad weather when pilots are unable to see the environment and for avoiding
distances to other aircraft that are too small [ 29 , 30 ].
14.2.4 Weather Conditions and Airport Operating Minima
In the beginning, landmarks were the only way for pilots to safely navigate. The
pilot had to see other airplanes in order to avoid collisions. Clouds, fog, and other
weather conditions restricted a pilot's sight. Therefore, safe flying required that
limits of visual conditions had to be established.
Airport operating minima expresses the weather limits of the usability of an
airport for takeoff, landing in a precision approach, or landing in a non-precision
approach. The terms used are ''visibility'' or ''runway visual range'', ''decision
altitude'' or ''minimum descent altitude'', and, if necessary, ''cloud condition'' [ 31 ].
Each participant, the airport, the airplane, and the pilot has its own minima.
Airport minima depend upon the available approach facilities. Aircraft minima are
based on on-board equipment. The personal minima of a pilot are determined by
his experience. The least favorable of these minima should be applied in practice,
including any increments required due to system failures.
14.2.5 Flight Rules
Flight rules play an important role in planning and carrying out fuel efficient flight,
for example through eliminating uncertainties that would otherwise increase the
need for surplus fuel. There are visual and instrument flight rules; see Table 14.3 .
There are still minimum conditions and limits which must prevail so that
takeoff or landing can be legally initiated. These conditions and limits vary
according to weather conditions, location, and the height of terrain and obstruc-
tions in the vicinity of the airport, the available equipment of the aircraft, and the
qualification of the crew [ 35 ].
Key factors in alleviating, the load on the environment besides expediting traffic
flow are good control practices creating airspace design with airways as straight as
possible, and new concepts such as Free Route Airspace Concept for free flying
areas [ 36 ]. There are specific airspaces within which users can freely plan their
routes between an entry point and an exit point, without references to the ATS
route network. In these airspaces, flights remain subject to ATC. Consequently and