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Three Simple Steps to Maintain Your FMS Battery

Feb 22, 2021

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Understand the FMS Battery

The Central Processing Unit (CPU) battery in Universal Avionics' Flight Management System (FMS) Navigation Computer Unit (NCU) generally lasts between three to seven years depending on its usage. For example, the FMS CPU battery is most active during power-off or in power standby mode.

Identify Battery Failure Warnings

When the FMS CPU battery begins to drain below standard levels, an FMC BATTERY LOW message will appear well before a battery failure to alert the user. You will see the message immediately (and only) after power-up and BEFORE the FMS initialization data is accepted. Many operators intuitively access the FMS Initialization Page before checking the MESSAGES and therefore, miss the FMC BATTERY LOW message. Please ensure your crew is informed of this important step. We have seen many operators miss the FMC BATTERY LOW message by assuming the Message Annunciation refers to other alerts that may be present on a regular basis, like the POSITION UNCERTAIN message that will always be present after power-on and completion of internal self-tests.

UA does not require regular scheduled maintenance on its FMSs and therefore, the FMS CPU battery is typically only replaced if there is a failure. Some operators of fleet aircraft using maintenance tracking systems like CAMPS may require FMS CPU battery replacement on a regular interval in conjunction with a calendar inspection. Another method to avoid battery failure is to add a procedure to check the message page when the Message Annunciator is present prior to initialization.

Know How to Replace the Battery

When it’s time to replace your FMS CPU battery, please send your unit to UA’s Tucson Repair Station, following the RMA Process outlined here to help prevent any delays in shipping. If preferred, you may contact your nearest UA Authorized Service Center to arrange for your battery replacement. Before sending your unit to the Service Center, please contact them directly to inquire about your FMS CPU battery, and whether they have the capability to conduct the replacement. The cost of an out of warranty battery replacement may vary depending on the age of your system. Please contact UA’s Support team to learn more.

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