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IAP. (Example: “maintain 2,000 until established
on the final approach course outbound, cleared
VOR/DME runway 12.”) The International Civil
Aviation Organization (ICAO) definition of established on course requires the aircraft to be within
half scale deflection for the ILS and VOR, or
within ±5° of the required bearing for the NDB.
Generally, the controller assigns an altitude compatible with glide slope intercept prior to being cleared
for the approach.
TYPES OF APPROACHES
In the NAS, there are approximately 1,033 VOR stations, 1,200 NDB stations, and 1,370 ILS installations,
including 25 LOC-Type Directional Aids (LDAs), 23
Simplified Directional Facilities (SDFs), and 242 LOC
only facilities. As time progresses, it is the intent of the
FAA to reduce navigational dependence on VOR,
NDB, and other ground-based NAVAIDs and, instead,
to increase the use of satellite-based navigation.
To expedite the use of RNAV procedures for all instrument pilots, the FAA has begun an aggressive schedule
to develop RNAV procedures. During 2002, the number
of RNAV/GPS approaches published in the NAS
exceeded 3,300, with additional procedures published
every revision cycle. While it had originally been the
plan of the FAA to begin decommissioning VORs,
NDBs, and other ground-based NAVAIDs, the overall
strategy has been changed to incorporate a majority
dependence on augmented satellite navigation while
maintaining a satisfactory backup system. This
backup system will include retaining all CAT II and
III ILS facilities and close to one-half of the existing
VOR network.
Each approach is provided obstacle clearance based on
the Order 8260.3 TERPS design criteria as appropriate
for the surrounding terrain, obstacles, and NAVAID
availability. Final approach obstacle clearance is different for every type of approach but is guaranteed from
the start of the final approach segment to the runway (not
below the MDA for nonprecision approaches) or MAP,
whichever occurs last within the final approach area.
Both pilots and ATC assume obstacle clearance responsibility, but it is dependent upon the pilot to maintain an
appropriate flight path within the boundaries of the final
approach area.
There are numerous types of instrument approaches
available for use in the NAS including RNAV (GPS),
ILS, MLS, LOC, VOR, NDB, SDF, and radar
approaches. Each approach has separate and individual
design criteria, equipment requirements, and system
capabilities.
VISUAL AND CONTACT APPROACHES
To expedite traffic, ATC may clear pilots for a visual
approach in lieu of the published approach procedure if
flight conditions permit. Requesting a contact
approach may be advantageous since it requires less
time than the published IAP and provides separation
from IFR and special visual flight rules (SVFR) traffic.
A contact or visual approach may be used in lieu of conducting a SIAP, and both allow the flight to continue as
an IFR flight to landing while increasing the efficiency
of the arrival.
VISUAL APPROACHES
When it is operationally beneficial, ATC may authorize
pilots to conduct a visual approach to the airport in lieu
of the published IAP. A pilot or the controller can initiate a visual approach. Before issuing a visual approach
clearance, the controller must verify that pilots have
the airport, or a preceding aircraft that they are to follow, in sight. In the event pilots have the airport in sight
but do not see the aircraft they are to follow, ATC may
issue the visual approach clearance but will maintain
responsibility for aircraft and wake turbulence separation. Once pilots report the aircraft in sight, they
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assume the responsibilities for their own separation
and wake turbulence avoidance.
A visual approach is an ATC authorization for an
aircraft on an IFR flight plan to proceed visually
to the airport of intended landing; it is not an IAP.
Also, there is no missed approach segment. An aircraft unable to complete a visual approach must
be handled as any other go-around and appropriate
separation must be provided. A vector for a visual
approach may be initiated by ATC if the reported
ceiling at the airport of intended landing is at least
500 feet above the MVA/MIA and the visibility is
3 SM or greater. At airports without weather reporting service there must be reasonable assurance (e.g.
area weather reports, PIREPs, etc.) that descent and
approach to the airport can be made visually, and the
pilot must be informed that weather information is
not available.
The visual approach clearance is issued to expedite the
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本文链接地址：
Instrument Procedures Handbook (IPH)仪表程序手册上(132)
