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ILS Performance
Most ILS installations are subject to signal interference by either surface vehicles
or aircraft. To prevent this interference, ILS critical areas are established near each
localizer and glide slope antenna. In the United States, vehicle and aircraft
operations in these critical areas are restricted any time the weather is reported less
than 800 foot ceiling and/or visibility is less than 2 miles.
Flight inspections of ILS facilities do not necessarily include ILS beam
performance inside the runway threshold or along the runway unless the ILS is
used for Category II or III approaches. For this reason, the ILS beam quality may
vary and autolands performed from a Category I approach at these facilities should
be closely monitored.
Flight crews must remember that the ILS critical areas are usually not protected
when the weather is above 800 foot ceiling and/or 2 mile visibility. As a result,
ILS beam bends may occur because of vehicle or aircraft interference. Sudden and
unexpected flight control movements may occur at a very low altitude or during
the landing and rollout when the autopilot attempts to follow the beam bends. At
ILS facilities where critical areas are not protected, flight crews should be alert for
this possibility and guard the flight controls (control wheel, rudder pedals and
thrust levers) throughout automatic approaches and landings. Be prepared to
disengage the autopilot and manually land or go-around.
The AFDS includes a monitor to detect significant ILS signal interference. If
localizer or glide slope signal interference is detected by the monitor, the autopilot
disregards erroneous ILS signals and remains engaged in an attitude stabilizing
mode based on inertial data. Most ILS signal interferences last only a short period
of time, in which case there is no annunciation to the flight crew other than erratic
movement of the ILS raw data during the time the interference is present. No
immediate crew action is required unless erratic or inappropriate autopilot activity
is observed.
If the condition persists, it is annunciated on the PFD. If the autopilot is engaged,
annunciations alert the flight crew that the autopilot is operating in a degraded
mode and the airplane may no longer be tracking the localizer or glide slope.
When the condition is no longer detected, the annunciations clear and the autopilot
resumes using the ILS for guidance.
October 31, 2006
777/787 Flight Crew Training Manual
Approach and Missed Approach
Copyright © The Boeing Company. See title page for details.
5.18 FCT 777/787 Preliminary (TM)
Autolands on Contaminated Runways
AFDS ROLLOUT mode performance cannot be assured when used on
contaminated runways. The ROLLOUT mode relies on a combination of
aerodynamic rudder control, nose wheel steering and main gear tracking to
maintain the runway centerline using localizer signals for guidance. On a
contaminated runway, nose wheel steering and main gear tracking effectiveness,
and therefore airplane directional control capability, is reduced. To determine the
maximum crosswind, use the most restrictive of the autoland crosswind
limitation, or during low visibility approaches, the maximum crosswind
authorized by the controlling regulatory agency. Consideration should also be
given to the Landing Crosswind Guidelines published in chapter 6 of this manual
or operator guidelines.
If an autoland is accomplished on a contaminated runway, the pilot must be
prepared to disengage the autopilot and take over manually should ROLLOUT
directional control become inadequate.
Low Visibility Approaches
A working knowledge of approach lighting systems and regulations as they apply
to the required visual references is essential to safe and successful approaches.
Touchdown RVR is normally controlling for Category I, II, and III approaches.
For Category I and II approaches, mid and rollout RVR are normally advisory. For
Category III operations mid and rollout RVR may be controlling. In some
countries, visibility is used instead of RVR. Approval from the regulatory agency
is required to use visibility rather than RVR.
During Category I approaches, visual reference requirements typically specify
that either the approach lights or other aids be clearly visible to continue below
DA(H). During Category I and II approaches, descent below 100 ft. above
touchdown zone elevation requires the red terminating bars or red side row bars
(ALSF or Calvert lighting systems, or ICAO equivalent, if installed) to be
distinctly visible. If actual touchdown RVR is at or above the RVR required for the
approach, the runway environment (threshold, threshold lights and markings,
　
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本文鏈接地址：787機組訓練手冊Flight Crew Training Manual 787(71)