Summary
The FAA is revising an earlier NPRM for an airworthiness directive (AD) that applies to various aircraft equipped with a Honeywell Primus II RNZ-850/-851 Integrated Navigation Unit (INU). The original NPRM would have superseded an existing AD that, as one alternative for compliance, provides for a one-time inspection to determine whether a certain modification has been installed on the Honeywell Primus II NV850 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, the existing AD provides for revising the aircraft flight manual to include new limitations for instrument landing system approaches. The original NPRM proposed to require inspecting to determine whether certain other modifications have been done on the NRM; and doing related investigative, corrective, and other specified actions, as applicable. The original NPRM resulted from reports of erroneous glideslope indications oncertain aircraft equipped with subject INUs. This new action revises the original NPRM by describing further modifications to address additional anomalies. We are proposing this supplemental NPRM to ensure that the flightcrew has an accurate glideslope deviation indication. An erroneous glideslope deviation indication could lead to the aircraft making an approach off the glideslope, which could result in impact with an obstacle or terrain.