Product Documents If you would like a copy of any of our user manuals, please contact us. We will email or mail you a copy promptly. TSO Related Documents TSO C139 Aircraft Audio Systems and Equipment Basic information about the documents used to certify audio systems in aircraft. The RTCA performance and environmental documents referenced in this document are only available by purchase through the RTCA website. FAA InFO bulletin 07001 Bulletin in which the FAA expressed concern about the possibility that Acoustic Noise Reduction (ANR) headsets may attenuate too much in the cockpit and mask critical sounds. Note that no mention of TSO is made in the document. Official FAA response to use of TSO and non-TSO headsets in Part 121 Operations When concern over various interpretation of the FARs about the use of TSO and non-TSO headsets in Part 121 operations, an official request of interpretation was made. This is the response received from the FAA in Washington. Other Documents 2008 Survey on Headset Clarity, Quality & Safety Results of a 2008 survey of 500+ pilots comparing the clarity, quality and safety of different manufacturers of headsets. Note that this survey is not model specific.