(b)
LOC Mode Enable

 1)  The LOC enable logic is generated when LOC mode arm or APP arm and LOC deviation filter engage are a logic one. The LOC deviation filter engage is initially dependent on LOC in-range logic. Synchronization continues as in LOC mode arm. When runway correction enable is logic one, computation of filtered deviation distance is modified to be primarily controlled by cross runway acceleration.

 (c)
Two-Turn Capture (LOC2TC)

 1)  The following conditions determine the start of a two-turn capture. The threshold value of delta ground track (DGTRK) is the value below which LOC2TC becomes logic one (DPSIWN). It is the lesser of 20 degrees and a computed value which is a function of G/S attitude and filtered LOC deviation distance (DYLOCF). A divergent capture situation exists when the signs of DGTRK and DYLOCF are equal. When LOC2TC is logic one, LOC1TC is inhibited. Localizer capture (LOC CAPT) is generated by LOC 2 (LOC second phase).

 (d)
One-Turn Capture (LOC1TC)

 1)  When the computed B/A exceeds the minimum LOC capture turn B/A, LOC1TC logic is generated and LOC CAPT is generated. A latch maintains LOC CAPT and generates LOC CAPP (past value of LOC CAPT). Localizer signal and command synchronization is disabled to permit capture turns to be generated.
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MAINTENANCE MANUAL

 (e)  
LOC Linear

 1)  After the airplane has become aligned to the LOC centerline, LOC LINEAR is generated and the LOC TRACK submode is enabled. Delta runway track must be less than 90 degrees but final control in developing LOC LINEAR is the output of the localizer deviation rate computation. This computation is sensitive to all critical variables for LOC centerline acquisition. The LOC LINEAR logic modifies the control laws for improved centerline tracking.

 (f)  
LOC Engaged (LOC ENG)

 1)  The LOC ENG logic is generated by LOC CAPT. At the transition to LOC LINEAR, LOC ENG momentarily goes to zero. This supresses transients to the LOC command processor during entry into LOC LINEAR and permits synchronizing for final capture.
 (21) Localizer Mode Control Signal Flow (Fig. 11)
 (a)  
The localizer control laws produce commands to fly the necessary path to capture the beam center. The system initially controls ground track angle until an initial capture turn is commanded at the computed bank angle. Final capture of the beam centerline then starts using lateral position control. Overshoot and control activity is minimized by flying as much of the capture turn as possible at the computed bank angle. Compensation is provided for effects of turbulence, beam noise, and beam propagation irregularities.

 (b)  
LOC Mode Arm

 1)  The LOC command processor synchronizes to LOC displacement rate error (DYDOTE) and filtered LOC deviation distance (DYLOCF). The cross-runway integrator synchronizes to roll attitude (PHI). The DGTRK is multiplied by the sign of DYLOCF (|1) to generate the two turn bank angle command curve. The minimum bank angle is calculated as a function of complimentary filtered gear altitude. This sets the minimum value of the P2TURN limiter. The P2TURN signal is not used, however, if LOC2TC logic is zero. The P1TURN signal can only be computed when LOC ENG is logic one, but until LOC CAPT occurs, P1TURN is not used in processing.

 (c)  
LOC One-Turn Capture

 1)  The Sync-loops are opened by LOC ENG and LOC CAPT. At LOC CAP, the stored value of P1TURN (LOC Proportional roll command) is held through the signal latch. Subsequent changes of P1TURN have no effect. The P1TURN signal is applied through a | 5.0 deg bank cmd/sec limiter and then converted into cross-runway acceleration. This develops cross runway velocity. This velocity is compared with LOC displacement rate (DYDOT) and LOC displacement rate error (DYDOTE) is produced. This error is converted to a proportional roll command and applied to a summing point. The other input to the summing point is zero, so the LOC proportional command is the only command generated at the initial capture turn.
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