1) Localizer deviation distance (ft) is the horizontal distance from the localizer centerline to the airplane. Localizer deviation rate (ft/sec) is a function of the cross-localizer centerline velocity. Cross-runway acceleration is in ft/sec.. The angle between ground track and runway heading is called delta runway track.
(b)
Raw Data Inputs
1) Runway heading information comes from the ILS control panel. The Inertial Reference System (IRS) provides ground speed and ground track data.
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(c)
LOC Capture
1) Localizer capture occurs when LOC capture criteria are satisfied. Capture criteria threshold is a variable point depending on values of the controlling factors listed above. It is calculated so that a smooth capture is achieved with minimum control activity and without overshoot beyond beam threshold. Localizer capture is inhibited when delta runway track exceeds 120 degrees.
(d)
Capture Flight Paths
1) If the delta runway track angle is so small that maintaining present track would cause intersecting the beam centerline too late or not at all, or if the angle is divergent up to 120 degrees, a two-turn capture (A) is commanded. A one-turn capture (C) is commanded if a sufficiently early beam center intersection is possible and a bank angle is computed to fly a circular flight path. One turn capture causes a beam center overshoot if the computed bank angle is greater than max bank angle allowed (B). The start of the capture turn on the flight path (C) is delayed until the minimum LOC capture bank angle is computed.
INNER MARKER MIDDLE
LOCALIZER
3000 Hz MARKER
DEVIATION
....... 1300 Hz OUTER
DISTANCE (FT)
Localizer Approach Geometry
Figure 16
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2) The capture turn is maintained at the commanded bank angle as long as possible, until computed rolldown rate to wings level is at the maximum permissible value. Control laws apply inertial smoothing to reduce effects of beam noise and propagation irregularities. Signal compensation is applied for gust filtering and crosswind shear effects.
(e)
Localizer Tracking
1) Control laws are modified when LOCLIN (LOC linear) criteria are satisfied, when lateral position and deviation rate have primary control. The LOCLIN criteria are functions of cross runway acceleration and LOC processing signal levels.
(f)
Control Law Objectives for LOC Operation
1) The objectives of localizer control laws are zero steady state error (eliminate LOC standoff error); max B/A commanded, 30 deg.; max roll rate commanded, 7 deg/sec, maximize disturbance rejection; minimize control activity, and avoid unnecessary overshoots.
(20) Localizer Mode Logic (Fig. 10)
(a)
LOC Mode Arm
1) The LOC mode arm logic is generated by pressing the LOC switch/light on the MCP, but is inhibited during the F/D disconnect pulse. This permits synchronization of the LOC signal and command processing so that the LOC integral and proportional roll commands are zero. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：757 AMM 飞机维护手册 自动飞行 AUTOFLIGHT 1(171)
