(4)
Prior to GS capture, the pitch channel uses either altitude hold or manual pitch commands to generate pitch steering commands. After GS capture, these are switched out and the pitch channel uses glide slope deviation signals and a pitchdown bias which causes an approximate 2 degrees pitchdown command. This bias is cancelled after 15 seconds by the low pass filter which passes changing signals but shunts steady-state signals. The glide slope deviation signal is applied from the navigation receiver to the computer and is proportional to the angular displacement of the airplane from the selected glide slope path. This signal is converted to ac and amplified. This amplification is controlled by the glide slope gain programming during approach and is described under Time Base Glide Slope Gain Programs. Glide slope deviation is amplified, fed to the glide slope capture sensor and is mixed with the pitch attitude signal to produce the pitch steering command signal.
(5)
The AUTO APP mode can also be initiated from the HDG mode. This is accomplished by first turning the flight director mode selector to the HDG position and then to the AUTO APP mode. The computer will operate in the HDG V/L submode until LOC capture. LOC capture will automatically arm the computer for capture of the glide slope beam. The computer will then operate in the AUTO APP mode as described above.
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H. GS MAN Mode
(1) In this mode of operation, automatic sensing of the glide slope beam, through the GS beam sensor is eliminated. A voltage from the mode selector switch, replaces the GS capture signal, and loss of GS AUTO mode voltage deactivates the sensor. Also, the annunciator will show G/S engaged (green).
I. Time Base Glide Slope Gain Programs (Fig. 3 and 4)
(1)
The purpose of glide slope gain programming is to reduce the pitch steering channel gain (by resistance-capacity time-constant circuitry). This enables the pilot to keep the airplane in the glide slope beam as he maneuvers the airplane to align the V-bars against the miniature airplane in the ADI despite beam irregularities and reduced beam width close in to the airfield. This pitch channel gain is the ratio of pitch command to glide slope deviation. The various gain parameters are preset to specified values. Pitch channel gain is automatically reduced by signal trips from the radio altimeter and marker beacon receiver systems.
(2)
Prior to commencement of gain program No. 1, with the mode selector set to AUTO APP, the pitch channel operates at a gain 1 level. Upon glide slope beam capture, and either upon receipt of a 1500-foot radio altimeter signal trip and RA VALID signal or upon an RA INVALID signal, the pitch channel gain is reduced from gain 1 over a 120-second period to nominal gain. This gain is then maintained until either a middle marker or 200-foot radio altimeter trip executes commencement of gain program No. 2 which is initiated by the GS-2 signal. The pitch channel gain is then further reduced from nominal gain to gain 2 over a 7.5-second period, and this gain figure is now maintained until either the airplane has landed, or go-around mode is selected.
(3)
If GS MAN mode is selected prior to the end of gain program No. 1, the GS manual signal is generated and the pitch channel gain is reduced immediately to nominal gain, eliminating the rest of gain program No. 1. However, gain program No. 2 will still follow as described above.
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Glide Slope Time Base Gain Programming 5A5
34-26-0 Figure 4 Feb 20/85
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J. GA Mode
(l) The GA (Go-Around) mode of operation is used for an aborted approach. In the GA mode, when the pilot aligns the V-bars against the miniature airplane in the ADI, the real airplane will be in a wings level 14-degree pitchup climbout angle. When initiated, the roll channel commands wings level and the pitch channel commands a 14-degree pitchup angle to the ADI. The system will automatically switch to GA, from either of the glide slope modes, by depressing the go-around switch on the thrust lever. This energizes the switch release solenoid and permits the mode selector to spring back to the GA position. When the system is in the GA mode, the GO AROUND lights on the annunciator displays will be on and the computer produces steering commands in the bank and pitch channels. In the bank channel, the computer receives bank error signals from the attitude reference system which are directed to the ADI as bank steering commands. The V-bars indicate the corrections necessary to keep the airplane level in a lateral plane. In the pitch channel, the computer receives and mixes pitch error signals from the attitude reference system with the 14-degree pitchup bias to produce pitch steering command signals. These steering command signals are transmitted to the V-bars in the ADI.The V-bars then indicate the necessary corrections to keep the airplane in the desired flight path in respect to pitch.
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