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时间:2010-05-22 22:46来源:蓝天飞行翻译 作者:admin
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builds the descent path upward and back in the direction of the FAF by starting at
the location of the missed approach waypoint (MAP) and its associated altitude
constraint. The FMC calculates this path using the coded GP angle, also called the
vertical angle. The MAP is normally shown on the LEGS page as a RWxx or
MXxx waypoint. In some cases a named waypoint is used as the MAP. A GP angle
is coded in the navigation database for nearly all straight-in approach procedures.
This GP angle is normally defined by the state authority responsible for the
approach procedure and provides a continuous descent at a constant flight path
angle for a final approach path that complies with minimum altitudes at
intermediate step down fixes. The typical GP angle is approximately 3.00°, but
can vary from 2.75° to 3.77°.
The projection of the vertical path upward and back toward the FAF along this
coded GP angle stops at the next higher limiting altitude in the vertical profile.
This limiting altitude is the more restrictive of the following:
• the “At” altitude on the constrained waypoint preceding the MAP
• the crossing altitude on the next “at or above” constrained waypoint
preceding the MAP
• the speed transition or the speed restriction altitude, whichever is lower
• cruise altitude.
October 31, 2004
767 Flight Crew Training Manual
Approach and Missed Approach
Copyright © The Boeing Company. See title page for details.
FCT 767 (TM) 5.39
The following examples show typical VNAV final approach paths where there is
a GP angle in the navigation database. The first example shows an RWxx missed
approach waypoint. The second example below shows the VNAV final approach
path where there is a missed approach waypoint prior to the runway. Note that in
the second case the projected path crosses the runway threshold at approximately
50 feet. VNAV guidance is level flight, however, when the airplane passes the
missed approach point. Both examples are for “At” altitude constraints at the FAF.
Note: The final approach course fix (FACF) is typically located on the final
approach course approximately 7 NM prior to the FAF. The FAF referred
to in the following procedures refers to the charted FAF and is intended to
mean the point at which the final approach descent is begun.
For the non-ILS approach procedures with an “At” constraint altitude at the FAF,
a short, level segment between the FAF and the final glide path (also called a
“fly-off”) may result. For the ILS procedure, the constraint altitude at the FAF is
computed to be the crossing altitude of the glide slope.
Coded vertical
angle
(RWxx)
Threshold
FACF FAF MAP crossing height
Coded vertical
angle
(MXxx)
Threshold
FACF FAF MAP crossing height
October 31, 2004
767 Flight Crew Training Manual
Approach and Missed Approach
Copyright © The Boeing Company. See title page for details.
5.40 FCT 767 (TM)
Crews can expect to see several other variations of approach path construction:
• approaches where the FAF has an “at or above” waypoint altitude
constraint. The GP angle normally terminates at the FACF altitude
constraint or the cruise altitude, whichever is lower. When this type of
path is flown, the airplane passes above the FAF.
• where there is more than one GP angle, such as for ILS approaches, the
airplane uses the GP angle for the active leg to define the VNAV approach
path. These types of paths are shown on the LEGS page as having two GP
angle values, one approaching the FAF, the second approaching the
runway (missed approach point).
Note: The coded GP angle is steeper than normal in temperatures warmer than
ISA standard and is shallower than normal in temperatures colder than ISA
standard.
October 31, 2004
767 Flight Crew Training Manual
Approach and Missed Approach
Copyright © The Boeing Company. See title page for details.
FCT 767 (TM) 5.41
Instrument Approach Using VNAV
Approaching intercept heading
• Flaps 5
• Flaps 5
On RADAR vectors
• HDG SEL
• Pitch mode (as needed)
Intercept heading
• Arm LNAV or select
other roll mode
• Flaps 1
FAF
Inbound (Approximately 2 NM)
• Gear down
• Flaps 20 (landing flaps 1 engine)
• Arm speedbrake
• Set DA(H) or MDA(H)
• Select VNAV
• Speed intervention
• Landing flaps (2 engine)
Enroute to fix
• LNAV or other roll mode
• VNAV or other pitch mode
 
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