@alanfernandes Ok, I did some digging. The Starship was originally designed in the 1980s and produced between 1989 and 1995. The original Collins AMS-850 had no GPS capability; it relied primarily on dual IRS with DME/DME and VOR/DME updating. However, the avionics suite was designed so that GPS sensors could be integrated later.
During the aircraft’s production run, many were equipped with dual Collins GPS-4000 LRUs feeding the FMS, likely in the early–mid 1990s. This allowed the system to fly basic LNAV GPS approaches, though the GPS was mainly used to improve long-term inertial navigation accuracy by providing position updates to the FMS.
The newer GPS-4000S units are generally backward-compatible replacements with higher precision and WAAS/SBAS capability, and they’re easier to source today since the GPS-4000/4000A units are no longer produced. Some Starships may have been upgraded to the 4000S, but since the AMS-850 predates many of the 4000S capabilities, it cannot use vertical guidance from WAAS approaches and would only benefit from improved integrity and lateral accuracy.
