2donkeys
When in 3D Mode, the Altitude displayed on the 430 and 530 is GPS-derived. Only when degraded to 2D mode by inadequate satellite coverage does the GPS fall back to display externally serialised altitude (such as from a transponder or blind encoder). It is this need for a fallback under conditions of poor satellite reception that drives the BRNAV requirement
The KLN94B is IFR approved and according to Honeywell UK is also BRNAV approved and it doesn't work as above. In the absence of a good enough GPS signal, no altitude at all is displayed.
Do you have a reference for the fallback of the GPS altitude to show the output of the altitude encoder instead, to enable BRNAV approval? The general idea is to use an altimeter for that purpose
