Business Aircraft LRU Battery Replacement

November 2011

Today’s aircraft are a mix and match of different levels of electronic technology. With the proliferation of electronic programmable modules in the 1980s and ‘90s came the need to install internal batteries into Line Replacable Units (LRUs) to hold information in memory for indefinite periods of time and make it available to other avionics components when a LRU was powered down. The first generation of equipment that required the installation of internal batteries revolved around Chapter 34 (navigation) systems. Flight Management, Loran-C and even early GPS receivers required the installation of small batteries that often allowed the system to retain data between power-up cycles.

With the advancement of digital avionics, the use of batteries in equipment only increased. Batteries are used today in many Attitude Heading and Reference (AHRS) units, Integrated Avionics Computers / Maintenance Diagnostic Computers (IACs / MDCs), Flight Management Computers (FMCs), Air Data Computers (ADCs) and other flight essential components. This has lead to a lot of questions. These components are often “on-condition,” meaning that there is no requirement from the manufacturer of the aircraft to identify or track the battery replacement cycle as part of their inspection program. The number of avionics components that have batteries will vary depending on the avionics suite.

Rockwell Collins, Honeywell, Universal, and other manufacturers have published recommended replacement cycles, which vary widely depending on aircraft utilization.

I recommended monitoring battery-dependent LRUs by adding them to your computerized maintenance tracking program if they are not already there. This will allow you to carry out battery replacements with other scheduled maintenance. Proper management of LRUs that utilize an internal battery will help reduce the risk of unscheduled maintenance and unnecessary cost.