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must be airborne prior to that time, or a release time. Pilots
should not take-off prior to the release time. Pilots can help
the controller by stating how soon they expect to be airborne.
If the void time is, for example, 10 minutes past the hour and
an aircraft is airborne at exactly 10 minutes past the hour,
the clearance is void—a pilot must take off prior to the void
time. A specific void time may be requested when filing a
flight plan.
ATC Towers
Several controllers in the tower cab are involved in handling
an instrument flight. Where there is a dedicated clearance
delivery position, that frequency is found in the A/FD and
on the instrument approach chart for the departure airport.
Where there is no clearance delivery position, the ground
controller performs this function. At the busiest airports, pretaxi
clearance is required; the frequency for pre-taxi clearance
can be found in the A/FD. Taxi clearance should be requested
not more than 10 minutes before proposed taxi time.
It is recommended that pilots read their IFR clearance back to
the clearance delivery controller. Instrument clearances can
be overwhelming when attempting to copy them verbatim,
but they follow a format that allows a pilot to be prepared
when responding “Ready to copy.” The format is: clearance
limit (usually the destination airport); route, including any
departure procedure; initial altitude; frequency (for departure
control); and transponder code. With the exception of the
transponder code, a pilot knows most of these items before
engine start. One technique for clearance copying is writing
C-R-A-F-T.
Assume an IFR flight plan has been filed from Seattle,
Washington to Sacramento, California via V-23 at 7,000
feet. Traffic is taking off to the north from Seattle-Tacoma
(Sea-Tac) airport and, by monitoring the clearance delivery
frequency, a pilot can determine the departure procedure
being assigned to southbound flights. The clearance limit
is the destination airport, so write “SAC” after the letter C.
Write “SEATTLE TWO – V23” after R for Route, because
departure control issued this departure to other flights. Write
“7” after the A, the departure control frequency printed on
the approach charts for Sea-Tac after F, and leave the space
after the letter T blank—the transponder code is generated by
computer and can seldom be determined in advance. Then,
call clearance delivery and report “Ready to copy.”
As the controller reads the clearance, check it against what
is already written down; if there is a change, draw a line
through that item and write in the changed item. Chances
are the changes are minimal, and most of the clearance is
copied before keying the microphone. Still, it is worthwhile
to develop clearance shorthand to decrease the verbiage that
must be copied (see Appendix 1).
Pilots are required to have either the text of a departure
procedure (DP) or a graphic representation (if one is
available), and should review it before accepting a clearance.
This is another reason to find out ahead of time which DP is
in use. If the DP includes an altitude or a departure control
frequency, those items are not included in the clearance.
The last clearance received supersedes all previous clearances.
For example, if the DP says “Climb and maintain 2,000 feet,
expect higher in 6 miles,” but upon contacting the departure
controller a new clearance is received: “Climb and maintain
8,000 feet,” the 2,000 feet restriction has been canceled. This
rule applies in both terminal and Center airspace.
9-6
Figure 9-7. Combined Radar and Beacon Antenna. Figure 9-8. Minimum Vectoring Altitude Chart.
When reporting ready to copy an IFR clearance before the
strip has been received from the Center computer, pilots
are advised “clearance on request.” The controller initiates
contact when it has been received. This time can be used for
taxi and pre-takeoff checks.
The local controller is responsible for operations in the Class
D airspace and on the active runways. At some towers,
designated as IFR towers, the local controller has vectoring
authority. At visual flight rules (VFR) towers, the local
controller accepts inbound IFR flights from the terminal radar
facility and cannot provide vectors. The local controller also
coordinates flights in the local area with radar controllers.
Although Class D airspace normally extends 2,500 feet above
field elevation, towers frequently release the top 500 feet to
the radar controllers to facilitate overflights. Accordingly,
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Instrument Flying Handbook仪表飞行手册下(60)
