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on automated weather observation systems.
CENTER WEATHER
In the event that an airport has weather observation capability, but lacks the appropriate equipment to transmit
that information over a radio frequency, air route traffic
control centers (ARTCCs) can provide flight crews with
hourly METAR or non-routine (special) aviation
weather report (SPECI) information for those airports.
For example, as an aircraft approaches an airport, the
center controller can voluntarily or upon request provide
the pilot with the most recent weather observation.
Terminal Radar Approach Control (TRACON) facilities
also provide weather observation information on a workload-permitting basis. Another option to obtain a current
METAR or SPECI is to contact an En Route Flight
Advisory Service facility (Flight Watch).
REGULATORY REQUIREMENTS
There are many practical reasons for reviewing weather
information prior to initiating an instrument approach.
Pilots must familiarize themselves with the condition
of individual airports and runways so that they may
make informed decisions regarding fuel management,
diversions, and alternate planning. Because this information is critical, CFRs require pilots to comply with
specific weather minimums for planning and execution
of instrument flights and approaches.
PART 91 OPERATORS
According to Part 91.103, the pilot in command must
become familiar with all available information concerning a flight prior to departure. Included in this
directive is the fundamental basis for pilots to review
NOTAMs and pertinent weather reports and forecasts
for the intended route of flight. This review should
include current weather reports and terminal forecasts
for all intended points of landing and alternate airports.
In addition, a thorough review of an airport’s current
weather conditions should always be conducted prior
to initiating an instrument approach. Pilots should also
consider weather information as a planning tool for fuel
management.
For flight planning purposes, weather information
must be reviewed in order to determine the necessity
and suitability of alternate airports. For Part 91 operations, the 600-2 and 800-2 rule applies to airports with
precision and nonprecision approaches, respectively.
Approaches with vertical guidance (APV) are considered semi-precision and nonprecision since they do not
meet the International Civil Aviation Organization
(ICAO) Annex 10 standards for a precision approach.
(See Final Approach Segment section later in this
chapter for more information regarding APV
approaches.) Exceptions to the 600-2 and 800-2 alternate minimums are listed in the front of the National
Aeronautical Charting Office (NACO) U.S. Terminal
Procedures Publication (TPP) and are indicated by an
“ ” symbol on the approach charts for the airport.
This does not preclude flight crews from initiating
instrument approaches at alternate airports when the
weather conditions are below these minimums. The
600-2 and 800-2 rules, or any exceptions, only apply to
flight planning purposes, while published landing minimums apply to the actual approach at the alternate.
PART 135 OPERATORS
Unlike Part 91 operators, Part 135 operators may not
depart for a destination unless the forecast weather
there will allow an instrument approach and landing.
According to Part 135.219, flight crews and dispatchers
may only designate an airport as a destination if the latest weather reports or forecasts, or any combination of
them, indicate that the weather conditions will be at or
above IFR landing minimums at the estimated time of
arrival (ETA). This ensures that Part 135 flight crews
consider weather forecasts when determining the
suitability of destinations. Departures for airports
can be made when the forecast weather shows the
airport will be at or above IFR minimums at the
ETA, even if current conditions indicate the airport
to be below minimums. Conversely, Part 135.219
prevents departures when the first airport of intended
landing is currently above IFR landing minimums,
but the forecast weather is below those minimums at
the ETA.
Another very important difference between Part 91
and Part 135 operations is the Part 135 requirement
for airports of intended landing to meet specific
weather criteria once the flight has been initiated. For
Part 135, not only is the weather required to be forecast at or above IFR landing minimums for planning a
departure, but it also must be above minimums for initiation of an instrument approach and, once the
approach is initiated, to begin the final approach segment of an approach. Part 135.225 states that pilots
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Instrument Procedures Handbook (IPH)仪表程序手册上(106)
