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Joliet VOR at or above 12,000, descend and maintain
5,000.” This clearance authorizes you to descend from
your current altitude whenever you choose, as long as
you cross the Joliet VOR at or above 12,000 feet MSL.
After that, you should descend at a normal rate until you
reach the assigned altitude of 5,000 feet MSL.
Clearances to descend at pilot’s discretion are not just
an option for ATC. You may also request this type of
clearance so that you can operate more efficiently. For
example, if you are en route above an overcast layer,
you might ask for a descent at your discretion to allow
you to remain above the clouds for as long as possible.
This might be particularly important if the atmosphere
is conducive to icing and your aircraft’s icing protection
is limited. Your request permits you to stay at your cruising altitude longer to conserve fuel or to avoid prolonged
IFR flight in icing conditions. This type of descent can
also help to minimize the time spent in turbulence by
allowing you to level off at an altitude where the air is
smoother.
APPROACH CLEARANCE
The approach clearance provides guidance to a position
from where you can execute the approach, and it also
clears you to fly that approach. If only one approach procedure exists, or if ATC authorizes you to execute the
approach procedure of your choice, the clearance may
be worded as simply as “… cleared for approach.” If
ATC wants to restrict you to a specific approach, the
controller names the approach in the clearance—for
example, “…cleared ILS Runway 35 Right approach.”
When the landing will be made on a runway that is not
aligned with the approach being flown, the controller
may issue a circling approach clearance, such as
“…cleared for VOR Runway 17 approach, circle to land
Runway 23.”
When cleared for an approach prior to reaching a holding fix, ATC expects the pilot to continue to the holding
fix, along the feeder route associated with the fix, and
then to the IAF. If a feeder route to an IAF begins at a
fix located along the route of flight prior to reaching
the holding fix, and clearance for an approach is
issued, the pilot should commence the approach via the
published feeder route. The pilot is expected to commence the approach in a similar manner at the IAF, if
the IAF is located along the route to the holding fix.
ATC also may clear an aircraft directly to the IAF by
using language such as “direct” or “proceed direct.”
Controllers normally identify an approach by its published name, even if some component of the approach
aid (such as the glide slope of an ILS) is inoperative or
unreliable. The controller uses the name of the
approach as published but advises the aircraft when
issuing the approach clearance that the component is
unusable.
PRESENT POSITION DIRECT
In addition to using National Aeronautical Charting
Office (NACO) high and low altitude en route charts as
resources for your arrival, NACO area charts can be
helpful as a planning aid for situational awareness.
Many pilots find the area chart helpful in locating a
depicted fix after ATC clears them to proceed to a fix
and hold, especially at unfamiliar airports.
Looking at Figures 4-6, and 4-7 on page 4-8, assume
you are V295 northbound en route to Palm Beach
International Airport. You are en route on the airway
when the controller clears you present position direct to
the outer marker compass locator and for the instrument
landing system (ILS) approach. There is no transition
authorized or charted between your present position and
the approach facility. There is no minimum altitude published for the route you are about to travel.
In Figure 4-6, you are just north of HEATT Intersection
at 5,000 feet when the approach controller states,
“Citation 9724J, 2 miles from HEATT, cleared present
position direct RUBIN, cleared for the Palm Beach ILS
Runway 9L Approach, contact Palm Beach Tower on
119.1 established inbound.” With no minimum altitude
published from that point to the RUBIN beacon, you
should maintain the last assigned altitude until you reach
the IAF (that’s the fix, not the facility). Then, in Figure
4-7 on page 4-8, after passing the beacon outbound,
commence your descent to 2,000 feet for the course
reversal.
The ILS procedure relies heavily on the controller’s
recognition of the restriction upon you to maintain
your last assigned altitude until “established” on a published segment of the approach. Refer to Appendix B,
　
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本文鏈接地址：Instrument Procedures Handbook (IPH)儀表程序手冊上(91)