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Understanding The Impact Of Universal Avionics Legacy UNS-1 FMS Systems

May 2021


Universal Avionics has fielded over 30,000 FMS systems in over 50 different types of aircraft since 1983. There are vast numbers of UNS-1 equipped aircraft operating, of which many are now dealing with obsolescence and increased operating costs. If you operate one of the following FMSes then your FMS is considered to be a Legacy FMS:

  • UNS-1B/1B+
  • UNS-1C/1Csp/1C+/1CSP+
  • UNS-1D/1D+/1K/1K+
  • UNS-1M/1Msp
  • UNS-1JR, UNS-1, UNS-1A

Legacy FMSes face several issues as they age. Universal Avionics has supported these products for well over 20 years, but the availability of repair parts is becoming a huge problem. Parts obsolescence for LCDs, CPU boards, GPS boards, and GPS sensors limits their repair capabilities. Universal Avionics will do everything they can to keep your FMS in service, but the situation is only going to get worse over time.

The constraints the legacy FMS puts on your operations in today’s airspace is also an issue to consider.  The legacy FMS memory capacity and older Data Transfer Units are placing restrictions on operators.  Many legacy FMSes don’t have the storage capacity to hold the entire world navigation database. Sometimes this forces the aircrew to land the aircraft enroute to load a new section of the Nav database.  

The world’s magnetic variation model is changing.  The older FMS cannot apply forecast changes in magnetic variation, and as the years progress this will add more and more error into the FMS computed aircraft position. Especially in the Northern and Southern Latitudes.

Eventually, parts obsolescence, repair costs, and operational limitations will force every legacy FMS operator to replace his FMS.

When Is A Good Time To Upgrade?

The answer to this question is unique to every operator. Are operating costs, decreased inflight efficiency, and lack of data com driving cost per flying hour up. Is reducing the aircrew’s workload important? Are you concerned with protecting the resale value of your aircraft?

Upgrading your legacy FMS to a Universal SBAS-FMS pays for itself with reduced operating costs. The ADS-B Out approved sensor allows for more efficient routing leading to shorter trips and reduced cost. LPV and RNP approaches provide for precision approach minimums at more and more airports. Data link gets you in the air quicker and reduces weather impacts to your mission.

There are many things to consider. The experts at Duncan Aviation are always ready to answer your questions. Pick up the phone or send us an email, and we’ll do our best to help you make an educated decision.

Due to variances in aircraft system configurations and capabilities, please contact your Duncan Aviation Avionics Sales Representative for specific aircraft information and applicability.