EASA SIB 2008-58R1
Garmin non-WAAS GNS 400 and GNS 500 units - Unintended 8.33 kHz / 25 kHz Channel Spacing Switching
Summary
EASA Safety Information Bulletin 2008-58R1 addresses an issue with Garmin non-WAAS GNS 400 and GNS 500 units installed on various Part 23 certificated aircraft. The bulletin informs operators that these units may experience unintended switching between 8.33 kHz and 25 kHz channel spacing, causing garbled audio reception. The document highlights the affected software versions and provides guidance on resolving the issue.
What Changed
This bulletin introduces awareness of a known issue where adjusting standby frequencies with different channel spacing causes the active receiver to switch erroneously, affecting audio quality. Garmin has developed software updates (Service Bulletins 0844 for GNS 400 and 0845 for GNS 500) to correct this deficiency. Immediate operational workarounds and future software corrections are detailed.
Why It Matters
The issue can degrade communication quality by causing garbled audio or reception disturbances, which may impact flight safety and situational awareness. Operators and maintenance personnel need to understand the problem to ensure reliable radio communications and maintain compliance with European channel spacing regulations. Awareness of the software update availability helps plan timely maintenance actions.
What To Do
Operators should follow Garmin's immediate action by pressing the COM Flip-flop key twice if garbled reception occurs after changing standby frequencies. They should arrange for software updates to Main Software Version 5.04 for GNS 400 units and 6.04 for GNS 500 units as soon as possible. For further assistance, contact Garmin Europe Product Support or EASA Airworthiness Directives office.
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