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on published routes to it, radar service is automatically
terminated when the landing is completed; or when
instructed to change to advisory frequency at airports
without an operating air traffic control tower,
whichever occurs first. When arriving on an IFR flight
plan at an airport with an operating control tower, the
flight plan will be closed automatically upon landing.
The extent of services provided by approach control
varies greatly from location to location. The majority of
Part 121 operations in the NAS use airports that have
radar service and approach control facilities to assist
in the safe arrival and departure of large numbers of
aircraft. Many airports do not have approach control
facilities. It is important for pilots to understand the
differences between approaches with and without an
approach control facility. For example, consider the
Durango, Colorado, ILS DME RWY 2 and low altitude en route chart excerpt, shown in figure 5-11.
• High or lack of minimum vectoring altitudes
(MVAs) – Considering the fact that most modern
commercial and corporate aircraft are capable of
direct, point-to-point flight, it is increasingly
important for pilots to understand the limitations
of ARTCC capabilities with regard to minimum altitudes. There are many airports that
are below the coverage area of Center radar,
and, therefore, off-route transitions into the
approach environment may require that the
aircraft be flown at a higher altitude than
would be required for an on-route transition.
In the Durango example, an airplane approaching from the northeast on a direct route to the
Durango VOR may be restricted to a minimum
IFR altitude (MIA) of 17,000 feet mean sea
level (MSL) due to unavailability of Center radar
coverage in that area at lower altitudes. An
arrival on V95 from the northeast would be able to
descend to a minimum en route altitude (MEA)
of 12,000 feet, allowing a shallower transition
to the approach environment. An off-route
arrival may necessitate a descent in the published holding pattern over the DRO VOR to
avoid an unstable approach into Durango.
• Lack of approach control terrain advisories –
Flight crews must understand that terrain
clearance cannot be assured by ATC when aircraft are operating at altitudes that are not
served by Center or approach radar. Strict
adherence to published routes and minimum
altitudes is necessary to avoid a controlled
flight into terrain (CFIT) accident. Flight
crews should always familiarize themselves
with terrain features and obstacles depicted on
approach charts prior to initiating the approach.
Approaches outside of radar surveillance require
enhanced awareness of this information.
• Lack of approach control traffic advisories – If
radar service is not available for the approach, the
ability of ATC to give flight crews accurate traffic
advisories is greatly diminished. In some cases,
the common traffic advisory frequency (CTAF)
may be the only tool available to enhance an IFR
flight’s awareness of traffic at the destination
airport. Additionally, ATC will not clear an
IFR flight for an approach until the preceding aircraft on the approach has cancelled
IFR, either on the ground, or airborne once in
visual meteorological conditions (VMC).
AIRPORTS WITH AN AIR TRAFFIC CONTROL TOWER
Towers are responsible for the safe, orderly, and expeditious flow of all traffic that is landing, taking off,
operating on and in the vicinity of an airport and, when
the responsibility has been delegated, tow ers
5-14
also provide for the separation of IFR aircraft in
terminal areas. Aircraft that are departing IFR
are integrated into the departure sequence by the
tower. Prior to takeoff, the tower controller
coordinates with departure control to assure
adequate aircraft spacing.
AIRPORTS WITHOUT AN
AIR TRAFFIC CONTROL TOWER
From a communications standpoint, executing an
instrument approach to an airport that is not served by
an ATC tower requires more attention and care than
making a visual approach to that airport. Pilots are
expected to self-announce their arrival into the vicinity
of the airport no later than 10 NM from the field.
Depending on the weather, as well as the amount and
type of conflicting traffic that exists in the area, an
approach to an airport without an operating ATC tower
will increase the difficulty of the transition to visual
flight. In many cases, a flight arriving via an instrument
approach will need to mix in with visual flight rules
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Instrument Procedures Handbook (IPH)仪表程序手册上(112)
