At LOC capture, the active roll mode changes to LOC. The MCP heading/track window changes to the ILS course.
At G/S capture, the active pitch mode changes to G/S.
The AFDS supplies an ILS tune inhibit signal when G/S and LOC are active with the autopilot system engaged.
The AFDS also supplies an ILS tune inhibit signal when the autopilot is not engaged and all of these conditions are true:
*
A flight director is on
*
G/S and LOC are active
*
The airplane is below 500 feet of radio altitude.
If the autopilot is not engaged and pilot tunes the ILS when the radio altitude is 500 feet or more, the flight director displays go out of view.
With LOC and/or G/S captured, the APP mode goes away by one of these methods:
*
Select another pitch mode if only G/S is active
*
Select another roll mode including LOC, if only LOC is active
*
Push either TO/GA switch if G/S is active, or the trailing edge flaps are not up
*
Disengage the autopilot and put the F/D switches in the off position
*
Push the APP switch if the airplane is above 1500 feet and both LOC and G/S are active.
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The last method lets the flight crew disconnect the APP mode if air traffic control sends the airplane to another runway. The flight crew sets a new ILS frequency and ILS course and pushes the APP switch to arm LOC and G/S again.
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General
In autoland, the AFDS controls the elevator for these functions:
*
Glideslope (G/S)
*
Flare
*
Touchdown.
The flare mode and touchdown sub-mode occur when the autopilot is engaged and at least two AFDCs operate.
Glideslope
With the G/S mode active, the AFDS keeps the airplane on the vertical descent flight path.
With the autopilot engaged and G/S and LOC modes active, these events occur as the airplane descends below 1500 feet:
*
The other control column and wheel backdrive actuators and both rudder pedal actuators engage. All available backdrive actuators engage.
*
LAND 3, LAND 2 or NO AUTOLAND shows on the PFD as the active autoland status
*
ROLLOUT and FLARE modes arm and show on the PFD.
*
The runway alignment sub-mode is active. There is no added annunciation for runway alignment on the PFD.
Flare/Touchdown
FLARE replaces G/S as the active mode on the PFD.
During flare, airplane touchdown occurs 450 feet past the glideslope transmitter at a descent rate of 1.5 feet/second.
The altitude at which the flare mode becomes active is flare height. The descent rate of the airplane sets this height. An adjustable flare height gives constant touchdown performance for a wide range of approach speeds.
The AFDS sends a throttle idle command to the TMCF at 25 feet radio altitude.
An airplane nose down command brings the nose wheel in contact with the runway. This occurs when the radio altitude is below five feet and the pitch attitude of the airplane is less than two degrees. At this time, the pitch mode goes blank on the PFD.
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General
The runway alignment function corrects for engine out and crosswind conditions during an autoland. This is to make sure the wings are level or the upwind wing is low for all possible wind and engine out combinations. The AFDS does this with rudder and aileron commands (sideslip).
At landing, the rollout mode controls rudder and nosewheel steering to keep the airplane on the center line of the runway.
Crosswind Runway Alignment
Crosswind control occurs at 500 feet or 200 feet.
When the crab angle is more than ten degrees (high crosswinds), the alignment occurs at 500 feet. The AFDS command decreases the crab angle by five degrees.
When the crab angle is between five and ten degrees (medium crosswinds), alignment occurs at 500 feet. Another alignment occurs at 200 feet. The total crab angle reduction for both alignments is five degrees.
When the crab angle is less than five degrees (light crosswinds), alignment occurs at 200 feet. The AFDS removes the crab angle.
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本文链接地址：777 AMM 飞机维护手册 自动飞行 Autoflight(19)
