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• ATC may ask you to descend to and maintain a
specific altitude. Generally, this clearance is for en
route traffic separation purposes, and you need to
respond to it promptly. Descend at the optimum
rate for your aircraft until 1,000 feet above the
assigned altitude, then descend at a rate between
500 and 1,500 feet per minute (FPM) to the
assigned altitude. If at any time, other than when
slowing to 250 KIAS at 10,000 feet MSL, you cannot descend at a rate of at least 500 FPM, advise
ATC.
• The second type of clearance allows you to
descend “… at pilot’s discretion.” When ATC
Figure 4-5. Instead of flying for a specific time after passing the holding fix, these holding patterns use distances to mark where the turns are made. The distances come from DME or IFR-certified GPS equipment.
". . . Bonanza 8394K, hold
northeast of the 16 DME
fix on the 030° radial of
the StedmanVORTAC,
five mile legs . . ."
". . . Viking 5786P, hold east of the 20
DME fix on the 265° radial of the Stedman
VORTAC, 5 mile legs . . ."
4-6
issues a clearance to descend at pilot’s discretion,
you may begin the descent whenever you choose
and at any rate you choose. You also are authorized to level off, temporarily, at any intermediate
altitude during the descent. However, once you
leave an altitude, you may not return to it.
A descent clearance may also include a segment where
the descent is at your discretion—such as “cross the
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
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Instrument Procedures Handbook (IPH)仪表程序手册下(86)
