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modes, as well as the associated auto-throttle modes.
This panel, sometimes called a mode control panel,
is normally accessible to both pilots. Most aircraft
with sophisticated auto-flight systems and autothrottles have the capability to select modes that
climb the airplane with maximum climb thrust and
descend the airplane with the throttles at idle (LVL
CHG, Flight Level Change [FL CHG], Manage
Level, etc.). They also have the capability to
“capture,” or level off at pre-selected altitudes, as
well as track a LOC and glide slope (G/S) or a VOR
course. If the airplane is RNAV equipped, the autopilot
will also track the RNAV generated course. Most of
these modes will be used at some point during an
instrument approach using the autopilot.
Additionally, these modes can be used to provide
flight director (FD) guidance to the pilot while
hand-flying the aircraft.
For the purposes of this precision approach example,
the auto-throttles are engaged when the autopilot is
engaged and specific airspeed and configuration
changes will not be discussed. The PF controls
airspeed with the speed selector on the mode control panel and calls for flaps and landing gear as
5-29
needed, which the PM will select. The example in
figure 5-20 begins with the airplane 5 NM northwest
of BROWN at 4,500 feet with the autopilot engaged,
and the flight has been cleared to track the Rwy 12
LOC inbound. The current roll mode is LOC with
the PF’s NAV radio tuned to the LOC frequency of
109.3; and the current pitch mode is altitude hold
(ALT HOLD). Approach control clears the airplane
for the approach. The PF makes no immediate
change to the autopilot mode to prevent the aircraft
from capturing a false glide slope; but the PM resets
the altitude selector to 2,200 feet. The aircraft will
remain level because the pitch mode remains in ALT
HOLD until another pitch mode is selected. Upon
reaching BROWN, the PF selects LVL CHG as the
pitch mode. The auto-throttles retard to idle as the
Figure 5-20. Example Approaches Using Autopilot.
5-30
airplane begins a descent. Approaching 2,200 feet,
the pitch mode automatically changes to altitude
acquire (ALT ACQ) then to ALT HOLD as the
airplane levels at 2,200 feet. In addition to slowing the airplane and calling for configuration
changes, the PF selects approach mode (APP). The
roll mode continues to track the LOC and the pitch
mode remains in ALT HOLD; however, the G/S
mode arms. Selecting APP once the aircraft has
leveled at the FAF altitude is a suggested technique
to ensure that the airplane captures the glide slope
from below, and that a false glide slope is not being
tracked.
The PF should have the aircraft fully configured for
landing before intercepting the glide slope to ensure a
stabilized approach. As the airplane intercepts the glide
slope, the pitch mode changes to G/S. Once the glide
slope is “captured” by the autopilot, the PM can select
the missed approach altitude in the altitude pre-selector, as requested by the PF. The airplane will continue
to track the glide slope. The minimum altitude at which
the PF is authorized to disconnect the autopilot is
airplane specific (Example, 50 feet below DA, DH,
or MDA but not less than 50 feet AGL). The PF can
disconnect the autopilot at any time prior to reaching
this altitude during a CAT I approach. The initial
missed approach is normally hand flown with flight
director guidance unless both autopilots are engaged
for autoland during a CAT II or III approach.
The differences when flying the underlying nonprecision approach begin when the aircraft has leveled off
at 2,200 feet. Once ALT HOLD is annunciated the
MDA is selected by the PM as requested by the PF. It
is extremely important for both pilots to be
absolutely sure that the correct altitude is selected
for the MDA so that the airplane will not inadvertently descend below the MDA. For aircraft that the
altitude pre-selector can only select 100-foot increments, the MDA for this approach must be set at 800
feet instead of 740 feet.
Vertical speed mode is used from the FAF inbound
to allow for more precise control of the descent. If
the pilots had not selected the MDA in the altitude
pre-selector window, the PF would not be able to
input a V/S and the airplane would remain level. The
autopilot mode will change from ALT ACQ to ALT
HOLD as the airplane levels at 800 feet. Once ALT
HOLD is annunciated, the PF calls for the missed
approach altitude of 4,000 feet to be selected in the
altitude pre-selector window. This step is very
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Instrument Procedures Handbook (IPH)仪表程序手册上(122)
