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Technical Standard Order (TSO) C-122a, Equipment That Prevent Blocked Channels Used in Two-Way Radio Communications Due to Simultaneous Transmissions

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This notice announces the FAA's intent to cancel TSO-C122a, Equipment That Prevent Blocked Channels Used in Two-Way Radio Communications Due to Simultaneous Transmissions. The effect of the cancelled TSO will not affect design or production according to an existing TSO authorization (TSOA). Articles produced under an existing TSOA can still be installed according to existing airworthiness approvals and applications for new airworthiness installation approvals will still be processed.


Comments must be received on or before July 23, 2012.


Mrs. Veronica Gardner, AIR-130, Federal Aviation Administration, 470 L'Enfant Plaza, Suite 4102, Washington, DC 20024. Telephone (202) 385-4690, fax (202) 385-4651, email to:


Comments Invited

You are invited to comment on the proposed cancellation of the TSO by submitting written data, views, or arguments to the above address. Comments received may be examined, both before and after the closing date at the above address, weekdays except federal holidays, between 8:30 a.m. and 4:30 p.m. The Director, Aircraft Certification Service, will consider all comments received on or before the closing date.


In 1984, the FAA was petitioned to enact rulemaking requiring two-way radio communication systems employing anti-blocking and stuck microphone protection circuitry. Our response to this rulemaking petition was the issuance of TSO-C128, Devices that Prevent Blocked Channels Used in Two-Way Radio Communications Due to Unintentional Transmissions, for preventing blocked channels used in two-way radio communication due to unintentional transmissions. TSO-C128, and the subsequent revision, has proven effective and popular with VHF radio manufacturers. Since 1994, there has been only one application for TSOA for TSO-C122a. Therefore, we believe it is appropriate to cancel TSO-C122a, given the eventual obsolescence of TSO-C122a equipment and the lack of industry interest in new TSO-C122a product designs. We continue to coordinate with industry's federal advisory committee through RTCA Special Committee (SC) 226, Audio Systems and Equipment, for any new developments on other means being used to address blocked channels caused by simultaneous transmissions.

Issued in Washington, DC, on June 18, 2012.

Susan J.M. Cabler,

Assistant Manager, Aircraft Engineering Division, Aircraft Certification Service.

[FR Doc. 2012-15238 Filed 6-21-12; 8:45 am]