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important because accurate FD guidance will not be
available to the PF during a missed approach if the
MDA is left in the window.
NOTE: See Maximum Acceptable Descent Rates
under the heading Descent Rates and Glidepaths for
Nonprecision Approaches.
STABILIZED APPROACH
In instrument meteorological conditions (IMC), you
must continuously evaluate instrument information
throughout an approach to properly maneuver the
aircraft (or monitor autopilot performance) and to
decide on the proper course of action at the decision
point (DA, DH, or MAP). Significant speed and configuration changes during an approach can seriously
degrade situational awareness and complicate the
decision of the proper action to take at the decision
point. The swept wing handling characteristics at
low airspeeds and slow engine-response of many turbojets further complicate pilot tasks during approach
and landing operations. You must begin to form a
decision concerning the probable success of an
approach before reaching the decision point. Your
decision-making process requires you to be able to
determine displacements from the course or glidepath centerline, to mentally project the aircraft’s
three-dimensional flight path by referring to flight
instruments, and then apply control inputs as necessary to achieve and maintain the desired approach
path. This process is simplified by maintaining a
constant approach speed, descent rate, vertical flight
path, and configuration during the final stages of an
approach. This is referred to as the stabilized
approach concept.
A stabilized approach is essential for safe turbojet
operations and commercial turbojet operators must
establish and use procedures that result in stabilized
approaches. A stabilized approach is also strongly
recommended for propeller-driven airplanes and helicopters. You should limit configuration changes at
low altitudes to those changes that can be easily
accommodated without adversely affecting your
workload. For turbojets, the airplane must be in an
approved configuration for landing or circling, if
appropriate, with the engines spooled up, and on the
correct speed and flight path with a descent rate of
less than 1,000 FPM before descending below the
following minimum stabilized approach heights:
• For all straight-in instrument approaches (this
includes contact approaches) in IFR weather conditions, the approach must be stabilized before
descending below 1,000 feet above the airport or
TDZE.
• For visual approaches and straight-in instrument
approaches in VFR weather conditions, the
approach must be stabilized before descending
below 500 feet above the airport elevation.
5-31
• For the final segment of a circling approach
maneuver, the approach must be stabilized 500
feet above the airport elevation or at the MDA,
whichever is lower.
These conditions must be maintained throughout the
approach until touchdown for the approach to be
considered a stabilized approach. This also helps you
to recognize a windshear situation should abnormal
indications exist during the approach.
DESCENT RATES AND GLIDEPATHS FOR
NONPRECISION APPROACHES
Maximum Acceptable Descent Rates: Operational
experience and research have shown that a descent
rate of greater than approximately 1,000 FPM is unacceptable during the final stages of an approach (below
1,000 feet AGL). This is due to a human perceptual
limitation that is independent of the type of airplane
or helicopter. Therefore, the operational practices and
techniques must ensure that descent rates greater than
1,000 FPM are not permitted in either the instrument
or visual portions of an approach and landing operation.
For short runways, arriving at the MDA at the MAP
when the MAP is located at the threshold may require a
missed approach for some airplanes. For nonprecision
approaches a descent rate should be used that will
ensure that the airplane reaches the MDA at a distance
from the threshold that will allow landing in the touchdown zone. On many IAPs this distance will be annotated by a VDP. To determine the required rate of
descent, subtract the TDZE from the FAF altitude and
divide this by the time inbound. For example if the
FAF altitude is 2,000 feet MSL, the TDZE is 400 feet
MSL and the time inbound is two minutes, an 800
FPM rate of descent should be used.
To verify the airplane is on an approximate 3° glidepath, use a calculation of “300-foot-to 1 NM.” The
glidepath height above TDZE is calculated by multiplying the NM distance from the threshold by 300.
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Instrument Procedures Handbook (IPH)仪表程序手册上(123)
