曝光台 注意防骗
网曝天猫店富美金盛家居专营店坑蒙拐骗欺诈消费者
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
weather. For example, airports with only a global positioning system (GPS) approach procedure cannot be used as an
alternate by TSO-C129/129A users even though the N/A
has been removed from the approach chart. For select
RNAV (GPS) and GPS approach procedures the N/A is
being removed so they may be used as an alternate by aircraft equipped with an approach approved WAAS receiver.
Because GPS is not authorized as a substitute means of navigation guidance when conducting a conventional approach
at an alternate airport, if the approach procedure requires
either DME or ADF, the aircraft must be equipped with the
appropriate DME or ADF avionics in order to use the
approach as an alternate.
For airplane Part 91 requirements, an alternate airport must
be listed on IFR flight plans if the forecast weather at the
destination airport, from a time period of plus or minus one
hour from the estimated time of arrival (ETA), includes ceil-
2-11
Figure 2-14. IFR Alternate Minimums.
2-12
ALTERNATE MINIMUMS FOR
COMMERCIAL OPERATORS
IFR alternate minimums for Part 121 and 135 operators
are very specific and have more stringent requirements
than Part 91 operators.
Part 121 operators are required by their OpsSpecs and
Parts 121.617 and 121.625 to have a takeoff alternate
airport for their departure airport in addition to their airport of intended landing if the weather at the departure
airport is below the landing minimums in the certificate
holder’s OpsSpecs for that airport. The alternate must be
within two hours flying time for an aircraft with three or
more engines with an engine out in normal cruise in still
air. For two engine aircraft, the alternate must be within
one hour. The airport of intended landing may be used
in lieu of an alternate providing it meets all the requirements. Part 121 operators must also file for alternate
airports when the weather at their destination airport,
from one hour before to one hour after their ETA, is
forecast to be below a 2,000-foot ceiling and/or less
than 3 miles visibility.
For airports with at least one operational navigational
facility that provides a straight-in non-precision
approach, a straight-in precision approach, or a circling
maneuver from an instrument approach procedure determine the ceiling and visibility by:
• Adding 400 feet to the authorized CAT I
HAA/HAT for ceiling.
• Adding one mile to the authorized CAT I visibility
for visibility minimums.
This is but one example of the criteria required for Part
121 operators when calculating minimums. Part 135
operators are also subject to their own specific rules
regarding the selection and use of alternate minimums
as outlined in their OpsSpecs and Part 135.219 through
Part 135.225, and they differ widely from those used by
Part 121 operators.
Typically, dispatchers who plan flights for these operators are responsible for planning alternate airports. The
dispatcher considers aircraft performance, aircraft
equipment and its condition, and route of flight when
choosing alternates. In the event changes need to be
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：
Instrument Procedures Handbook (IPH)仪表程序手册下(43)
