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may not begin an instrument approach unless the
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latest weather report indicates that the weather conditions are at or above the authorized IFR landing
minimums for that procedure. Part 135.225 provides relief from this rule if the aircraft has already
passed the FAF when the weather report is received.
It should be noted that the controlling factor for
determining whether or not the aircraft can proceed
is reported visibility. Runway visual range (RVR),
if available, is the controlling visibility report for
determining that the requirements of this section
are met. The runway visibility value (RVV),
reported in statute miles (SM), takes precedent over
prevailing visibility. There is no required timeframe
for receiving current weather prior to initiating the
approach.
PART 121 OPERATORS
Like Part 135 operators, flight crews and dispatchers
operating under Part 121 must ensure that the appropriate weather reports or forecasts, or any combination
thereof, indicate that the weather will be at or above the
authorized minimums at the ETA at the airport to which
the flight is dispatched (Part 121.613). This regulation
attempts to ensure that flight crews will always be able
to execute an instrument approach at the destination
airport. Of course, weather forecasts are occasionally
inaccurate; therefore, a thorough review of current
weather is required prior to conducting an approach.
Like Part 135 operators, Part 121 operators are
restricted from proceeding past the FAF of an
instrument approach unless the appropriate IFR
landing minimums exist for the procedure. In addition, descent below the minimum descent altitude
(MDA), decision altitude (DA), or decision height
(DH) is governed, with one exception, by the same
rules that apply to Part 91 operators. The exception is
that during Part 121 and 135 operations, the airplane
is also required to land within the touchdown zone
(TDZ). Refer to the section titled Minimum Descent
Altitude, Decision Altitude, and Decision Height later
in this chapter for more information regarding MDA,
DA, and DH.
PERFORMANCE CONSIDERATIONS
All operators are required to comply with specific
airplane performance limitations that govern
approach and landing. Many of these requirements
must be considered prior to the origination of flight.
The primary goal of these performance considerations
is to ensure that the aircraft can remain clear of obstructions throughout the approach, landing, and go-around
phase of flight, as well as land within the distance
required by the FAA. Although the majority of in-depth
performance planning for an instrument flight is normally done prior to the aircraft’s departure, a general
review of performance considerations is usually
conducted prior to commencing an instrument
approach.
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AIRPLANE PERFORMANCE OPERATING
LIMITATIONS
Generally speaking, air carriers must have in place
an approved method of complying with Subpart I of
Parts 121 and 135 (Airplane Performance Operating
Limitations), thereby proving the airplane’s performance capability for every flight that it intends
to make. Flight crews must have an approved
method of complying with the approach and landing
performance criteria in the applicable regulations
prior to departing for their intended destination.
The primary source of information for performance
calculations for all operators, including Part 91, is the
approved Aircraft Flight Manual (AFM) or Pilot’s
Operating Handbook (POH) for the make and model
of aircraft that is being operated. It is required to
contain the manufacturer determined performance
capabilities of the aircraft at each weight, altitude,
and ambient temperature that are within the airplane’s listed limitations. Typically, the AFM
for a large turbine powered airplane should contain
information that allows flight crews to determine
that the airplane will be capable of performing
the following actions, considering the airplane’s
landing weight and other pertinent environmental
factors:
• Land within the distance required by the regulations.
• Climb from the missed approach point (MAP)
and maintain a specified climb gradient with one
engine inoperative.
• Perform a go-around from the final stage of
landing and maintain a specified climb gradient with all engines operating and the airplane
in the landing configuration.
Many airplanes have more than one allowable flap
configuration for normal landing. Often, a reduced
flap setting for landing will allow the airplane to
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Instrument Procedures Handbook (IPH)仪表程序手册上(107)
