(c)
The auto throttle retards at 27 feet of radio altitude. The A channel autopilot provides a backup retard signal to the auto throttle which operates at Flare Eng plus 1.5-second delay, if radio altimeter failure occurs with single-channel autopilot operation.
(d)
Dual channel FLARE ENG annunciators indicate black on green at flare. Bank angle limits become + 4 degrees during flare mode.
(15)
Dual Channel AP Go-Around Mode
(a)
An automatic G/A mode is enabled in dual channel operation at FLARE ARM when the pitch and roll monitors are unbypassed (enabled). Selection of the mode is through go-around switches located on the thrust levers. G/A mode is annunciated on the FMA.
(b)
Minimum speed protection provides safe performance during automatic go-around. This is accomplished by a least-nose-up circuit which limits the pitch command to safe flight attitudes.
(c)
When G/A mode is selected, the thrust levers move forward to the G/A EPR limit. G/A commands a fixed pitch up attitude to stop the airplane descent rate and to provide initial climbout guidance. As the airplane altitude rate increases through the 10- to 20-fps region, a speed error command signal is added to the mode. The airspeed command is programmed as a function of flap position.
(d)
The G/A mode includes an alpha-max submode which is selected if the nominal speed/pitch attitude submode commands more nose-up than that allowed by the alpha-max submode. The alpha submode becomes the active mode only under severe downdraft/tail windshear conditions to help prevent airplane stick-shaker attitudes.
(e)
At G/A, a vertical gyro signal is coupled into the beam integrator to command and maintain a wings level attitude. Localizer, beam rate, and lateral accelerometer signal paths are switched out.
(f)
A roll cruise mode may be selected above 400 feet radio altitude. The system reverts to the selected first up channel roll cruise mode while the pitch axis remains in dual channel G/A. The pitch A/P G/A mode may transition into any valid cruise mode as long as the elevator trim is within single channel elevator authority. If not, mode selection is inhibited and, if ALT ACQ becomes enabled, the acquire does not take place and the A/P disengage light illuminates steady to command A/P disengagement and manual altitude acquire. Exiting pitch G/A also causes roll G/A to be exited. HDG SEL is automatically activated in roll if roll G/A has not already been exited. Pitch F/D G/A can also be exited by engaging single channel A/P. This results in automatic selection of LVL CHG and HDG SEL. When transitioning from A/P G/A in pitch, a cruise mode is obtained by selecting a pitch mode on the MCP or through altitude acquiring. No auto-selection of HDG SEL takes place when exiting pitch A/P G/A.
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L. Approach Mode Capabilities
(1)
The Approach (APP) mode capabilities are as follows: The mode will capture one axis at a time from any of the cruise modes and is compatible with any of the cruise modes of the uncaptured axis.
(2)
When the AP/FD glide slope (GS) mode is engaged, the only compatible A/T mode is A/T Speed mode with Go-Around EPR limit.
(3)
After the A/P Flare mode is engaged, the A/T will perform a throttle retard to the aft limit over a 6-second period beginning at 27 feet of radio altitude and will disengage 2 seconds after touchdown.
(4)
A missed approach (Go-Around) may be executed using dual AP after FLARE ARM or F/D (one or both) below 2000 feet radio altitude. Pushing either GA switch on the thrust levers activates the G/A mode. The A/T will go to the A/T EPR mode with a Go-Around EPR limit, whenever a GA is engaged.
(5)
Below 400 feet radio altitude, the only way out of the AP/FD G/A mode is to disengage the AP or switch to F/D to OFF.
(6)
Above 400 feet, a roll cruise mode may be activated while staying in pitch G/A. When exiting pitch G/A, roll G/A is also exited. When transitioning from a F/D G/A, a cruise mode is obtained by selecting a cruise mode on the MCP or through altitude acquiring.
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