Airworthiness Directives; Boeing Model 747-400, 757, 767, and 777 Series Airplanes Equipped With Allied Signal RIA-35B Instrument Landing System (ILS) Receivers

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This document proposes the supersedure of an existing airworthiness directive (AD), applicable to certain Boeing Model 747- 400, 757, 767, and 777 series airplanes, that currently requires a revision to the Airplane Flight Manual (AFM) to prohibit certain types of approaches. That action also requires repetitive inspections to detect certain faults of all RIA-35B ILS receivers, and replacement of discrepant ILS receivers with new, serviceable, or modified units; or, alternatively, an additional revision to the AFM and installation of a placard to prohibit certain operations. That AD was prompted by a report of errors in the glide slope deviation provided by an ILS receiver. This action would require accomplishment of the previously optional terminating action. The actions specified by the proposed AD are intended to prevent erroneous localizer deviation provided by faulty ILS receivers, which could result in a landing outside the lateral boundary of the runway.