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Universal FMS Common Battery Failures

January 2010

The Universal Flight Management System (FMS) has two batteries. One, located on the CPU board, supports Flight Plans while the other, located on the GPS board, supports the Almanac. During the initial start up, it is not uncommon to get a CPU Fail, Data Bus Fail or Ram Fail on the Universal FMS. Many times these are caused by one of the two FMS batteries being low and nearing the end of its useful life.

You begin to see these batteries fail after about three years of service. It is alway good practice to have them replaced within three years to avoid failures while on the road. A low battery will allow the system to continue working while displaying messages. However, if a battery is allowed to go completely dead before being changed, it will cause the system to stop during its self-test and display a red CPU Data Bus Fail. It will not allow the system to proceed until a new battery is installed.

On a FMS with only the Control Display Unit (CDU), the batteries are located in the CDU. On a FMS with both a CDU and Navigation Computer Unit (NCU), the batteries are located in the NCU.

For further information on Universal component maintenance battery replacement or to schedule maintenance, contact one of Duncan Aviation’s Avionics Technical Reps at 800.562.6377.