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• on an RNP based approach and an alert message indicates that ANP
exceeds RNP
• on a radar approach and radio communication is lost.
Landing Minima
Most regulatory agencies require visibility for landing minima. Ceilings are not
required. There are limits on how far an airplane can descend without visual
contact with the runway environment when making an approach. Descent limits
are based on a decision altitude/height DA(H) for approaches using a glide slope
or certain approaches using a VNAV path; or a MDA(H) for approaches that do
not use vertical guidance, or where a DA(H) is not authorized for use. Most
agencies do not require specific visual references below alert height (AH).
Approach charts use the abbreviation DA(H) or MDA(H). DA(H) applies to
Category I, II, and certain fail passive Category III operations. A decision altitude
“DA” or minimum descent altitude “MDA” is referenced to MSL and the
parenthetical height “(H)” is referenced to Touchdown Zone Elevation (TDZE) or
threshold elevation. Example: A DA(H) of 1,440’ (200’) is a DA of 1,440’ with a
corresponding height above the touchdown zone of 200’.
When RVR is reported for the landing runway, it typically is used in lieu of the
reported meteorological visibility.
October 31, 2006
777/787 Flight Crew Training Manual
Approach and Missed Approach
Copyright © The Boeing Company. See title page for details.
FCT 777/787 Preliminary (TM) 5.7
Radio Altimeter (RA)
A radio altimeter is normally used to determine DH when a DA(H) is specified for
Category II or Category III approaches, or to determine alert height (AH) for
Category III approaches. Procedures at airports with irregular terrain may use a
marker beacon instead of a DH to determine the missed approach point. The radio
altimeter may also be used to cross check the primary altimeter over known terrain
in the terminal area. However, unless specifically authorized, the radio altimeter
is not used for determining MDA(H) on instrument approaches. It should also not
be used for approaches where use of the radio altimeter is not authorized (RA
NOT AUTHORIZED). However, if the radio altimeter is used as a safety backup,
it should be discussed in the approach briefing.
Missed Approach Point (MAP)
A missed approach point is a point where a missed approach must be initiated if
suitable visual references are not available to make a safe landing or the airplane
is not in a position to make a safe landing.
Determination of a MAP
For approaches such as ILS or GLS, the DA(H) in conjunction with the glide slope
is used to determine the MAP. For non-ILS or G/S out approaches, two methods
for determining the MAP are acceptable in lieu of timing due to the accuracy of
FMC positioning:
• when arriving at the MDA(H) or DA(H) in conjunction with a VNAV
path
• if not using a VNAV path, use of the map display to determine when the
airplane has reached the VDP or the MAP. The approach legs along with
distance and time to the missed approach waypoint are displayed on the
map.
Timing During Approaches
Since FMC use is appropriate for instrument approach navigation, timing is not
the primary means to determine the missed approach point. The probability of
multiple failures that would result in timing being the only method of determining
the missed approach point is remote. However, some regulatory agencies may still
require the use of timing for approaches. The timing table, when included, shows
the distance from the final approach fix to the MAP.
Timing for instrument approaches is not necessary as long as there is no unable
RNP alert displayed.
October 31, 2006
777/787 Flight Crew Training Manual
Approach and Missed Approach
Copyright © The Boeing Company. See title page for details.
5.8 FCT 777/787 Preliminary (TM)
Instrument Landing System (ILS)
Arrival at the MAP is determined by reference to an altimeter. DA is determined
by reference to the barometric altimeter, while DH is determined by reference to
the radio altimeter.
Instrument Approach using VNAV
When specifically authorized by the instrument procedure and regulatory
authority, approaches may be flown to the following minima:
• a published VNAV DA(H)
• a published MDA(H) used as a decision altitude.
When either of the above minima are not specifically approved, use the published
MDA(H) + 50 feet as the MAP.
Localizer
For most localizer approaches, the published MAP is the threshold of the runway.
However, if a localizer approach is flown in VNAV PTH, use the missed approach
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787机组训练手册Flight Crew Training Manual 787(66)
