Airworthiness Directives; Boeing Model 747-400, 757, 767, and 777 Series Airplanes Equipped with AlliedSignal RIA-35B Instrument Landing System Receivers

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Boeing Model 747-400, 757, 767, and 777 series airplanes. This action requires a revision to the Airplane Flight Manual (AFM) to prohibit certain types of approaches if only one instrument landing system (ILS) receiver is operational. This 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. This AD also provides for optional terminating action for the AFM revisions and repetitive inspections. This amendment is prompted by a report of errors in the glide slope deviation provided by an ILS receiver. The actions specified in this AD are intended to detect and correct faulty ILS receivers, and to ensure that the flightcrew is advised of the potential hazard of performing ILS approaches using a localizer deviation from a faulty ILS receiver and also advised of the procedures necessary to address that hazard. Erroneous localizer deviation could result in a landing outside the lateral boundary of the runway.