AD FAA-2008-0556

The FAA is superseding an existing airworthiness directive (AD) that applies to certain Honeywell Primus II RNZ-850( )/-851( ) integrated navigation units (INUs). As one alternative for compliance, the existing AD provides for a one-time inspection to determine whether a certain modification has been installed on the Honeywell Primus II NV-850 navigation receiver module (NRM), which is part of the INU. In lieu of accomplishing this inspection, and for aircraft found to have an affected NRM, that AD provides for revising the aircraft flight manual to include new limitations for instrument landing system approaches. That AD also requires an inspection to determine whether certain other modifications have been done on the NRM; and doing related investigative, corrective, and other specified actions, as applicable; as well as further modifications to address additional anomalies. This AD extends the compliance time for a certain inspection and associated actions. This AD also revises the applicability to include additional affected INUs. This AD results from reports indicating that erroneous localizer and glideslope indications have occurred on certain aircraft equipped with the subject INUs. We are issuing this AD to ensure that the flightcrew has accurate localizer and glideslope deviation indications. An erroneous localizer or glideslope deviation indication could lead to the aircraft making an approach off the localizer, which could result in impact with an obstacle or terrain.