IFR GPS installations are more complex than for VFR.
? TSO C129 (C146 for WAAS) certified for enroute and terminal(A2) / approach(A1) operations.
? RAIM (Receiver Autonomous Integrity Monitoring) capable. Normally requires baro input from your altitude encoder then necessary redundancy with only four satellites.
? Must be coupled to an HSI or CDI.
? When the GPS is connected to the HSI or CDI a waypoint alert annunciator to indicate turn anticipation and impending waypoint passage.
? When the receiver approach mode is armed and when it is active.
? When the GPS is auto-sequencing for the approach or when auto-sequencing is temporarily suspended to allow a procedure turn or a vector.
? Current database (can verify fixes for enroute use)