# Proposed AD FAA-2004-18743: GARMIN International Inc. GTX 33, GTX 33D, GTX 330, and GTX 330D Mode S Transponders

- Type: Proposed airworthiness directive (not in force)
- Status: Became AD 2005-01-19
- Products: Garmin International
- Product type: Appliance
- Action: Notice of proposed rulemaking (NPRM).
- Published: October 6, 2004, Federal Register: October 7, 2004 (Volume 69, Number 194)
- Comments due: November 14, 2004
- Became: [AD 2005-01-19](https://openairdocs.org/ad/2005-01-19)
- Docket: FAA-2004-18743 (https://www.regulations.gov/docket/FAA-2004-18743, where comments are filed)
- Project: 2004-CE-23-AD
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/086412A77BEDB89786256F26004E701C.0001
- Page: https://openairdocs.org/proposed/FAA-2004-18743

## Summary

The FAA proposes to supersede Airworthiness Directive (AD) 2004-10-15, which applies to certain GTX 330 and GTX 330D Mode S transponders that are installed on airplanes. AD 2004-10-15 currently requires you to install GTX 330/330D Software Upgrade Version 3.03, 3.04, or 3.05. This proposed AD applies to certain GTX 33, GTX 33D, GTX 330, and GTX 330D Mode S transponders that are installed on airplanes and is the result of observations that the GTX 33/33D/330/330D may detect, from other airplanes, the S1 (suppression) interrogating pulse below the minimum trigger level (MTL) and, in some circumstances, not reply. The GTX 33/33D/330/330D should still reply even if it detects S1 interrogating pulses below the MTL. Consequently, this proposed AD would require you to install GTX 33/33D/330/330D Software Upgrade Version 3.03 or 3.06. Software Upgrade Versions 3.03 and 3.06 correct a TAS, TCAD, and TCAS I system "whisper-shout" problem that could potentially lead to the aircraft not being visible at certain ranges. TCAS II systems are not affected. We are issuing this proposed AD to prevent interrogating aircraft from possibly receiving inaccurate replies due to suppression from aircraft equipped with the GTX 33/33D/330/330D Mode S transponders when the pulses are below the MTL. The inaccurate replies could result in reduced vertical separation.

## Notices in this docket

- Oct 6, 2004: Notice of proposed rulemaking (NPRM). (first notice), comments due Nov 14, 2004 (https://drs.faa.gov/browse/excelExternalWindow/086412A77BEDB89786256F26004E701C.0001)

---
OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.