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typically the controlling visibility reference.
AUTOMATIC TERMINAL
INFORMATION SERVICE AND DIGITAL ATIS
The automatic terminal information service (ATIS) is
another valuable tool for gaining weather information. ATIS
is available at most airports that have an operating control
tower, which means the reports on the ATIS frequency are
only available during the regular hours of tower operation.
At some airports that operate part-time towers, ASOS/AWSS
information is broadcast over the ATIS frequency when the
tower is closed. This service is available only at those airports that have both an ASOS/AWSS on the field and an
ATIS-ASOS/AWSS interface switch installed in the tower.
Each ATIS report includes crucial information about runways and instrument approaches in use, specific outages,
and current weather conditions including visibility.
Visibility is reported in statute miles and may be omitted
if the visibility is greater than five miles. ATIS weather
information comes from a variety of sources depending
on the particular airport and the equipment installed there.
The reported weather may come from a manual weather
observer, weather instruments located in the tower, or
from automated weather stations. This information, no
matter the origin, must be from National Weather Service
approved weather sources for it to be used in the ATIS
report.
The digital ATIS (D-ATIS) is an alternative method of
receiving ATIS reports. The service provides text messages to aircraft, airlines, and other users outside the
standard reception range of conventional ATIS via
landline and data link communications to the cockpit.
Aircraft equipped with data link services are capable of
receiving ATIS information over their Aircraft
Communications Addressing and Reporting System
(ACARS) unit. This allows the pilots to read and print out
the ATIS report inside the aircraft, thereby increasing
report accuracy and decreasing pilot workload.
Also, the service provides a
computer-synthesized voice
message that can be transmitted to all aircraft within range
of existing transmitters. The
Terminal Data Link System
(TDLS) D-ATIS application
uses weather inputs from
local automated weather
sources or manually entered
meteorological data together
with preprogrammed menus
to provide standard information to users. Airports with D-
ATIS capability are listed in
the A/FD.
Figure 2-13. A/FD Entry for an AWOS Station.
Figure 2-12. ASOS Station Installation.
ings lower than 2,000 feet and/or visibility less than 3 SM. A
simple way to remember the rules for determining the necessity of filing an alternate for airplanes is the “1, 2, 3 Rule.”
For helicopter Part 91, similar alternate filing requirements
apply. An alternate must be listed on an IFR flight plan if the
forecast weather at the destination airport or heliport, from
the ETA and for one hour after the ETA, includes ceilings
lower than 1,000 feet, or less than 400 feet above the lowest
applicable approach minima, whichever is higher, and the
visibility less than 2 SM.
Not all airports can be used as alternate airports. An airport
may not be qualified for alternate use if the airport NAVAID
is unmonitored, or if it does not have weather reporting capabilities. For an airport to be used as an alternate, the forecast
weather at that airport must meet certain qualifications at
the estimated time of arrival. Standard alternate minimums
for a precision approach are a 600-foot ceiling and a 2 SM
visibility. For a non-precision approach, the minimums are
an 800-foot ceiling and a 2 SM visibility. Standard alternate minimums apply unless higher alternate minimums
are listed for an airport.
On NACO charts, standard alternate minimums are not
published. If the airport has other than standard alternate
minimums, they are listed in the front of the approach chart
booklet. The presence of a triangle with an on the approach
chart indicates the listing of alternate minimums should be
consulted. Airports that do not qualify for use as an alternate
airport are designated with an N/A. [Figure 2-14]
It is important to remember that ATIS information is
updated hourly and anytime a significant change in the
weather occurs. As a result, the information is not the
most current report available. Prior to departing the airport, you need to get the latest weather information from
the tower. ASOS/AWSS and AWOS also provide a source
of current weather, but their information should not be
substituted for weather reports from the tower.
IFR ALTERNATE REQUIREMENTS
The requirement for an alternate depends on the aircraft category, equipment installed, approach NAVAID and forecast
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Instrument Procedures Handbook (IPH)仪表程序手册上(47)
