SC-226 MEETING MINUTES Working Group JANUARY 14 ... - RTCA

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RTCA Paper No. 021-13/SC226-010 February 6, 2013 Sixth item of discussion: Discussion of oxygen mask inhale mic cutoff (or attenuation) switch feature that exists on some masks. The FAA rule concerning continuous hot mic recording seems like it could preclude this option from being acceptable for certification. However, there is prior certification experience in the industry that has allowed these masks to be accepted on aircraft. Some information from the participants about who has certified the oxygen mask with the inhale cutoff switch, and on what type of aircraft, would be useful to the committee to use as reference information. Greg Frye, FAA, has taken the action to ask around concerning the FAA’s position on the cutoff switch. However, regardless of the outcome of this research, he suggested that we should cover this feature within section 1 of the standard. Due to past involvement of NTSB in developing the rule, it would be beyond the scope of the committee to include a hardened requirement for it. Language within the rule includes the word “uninterrupted” and this would be taken by the FAA to mean that no interruption of CVR hot mic audio can occur. The oxygen mask participants of the committee took the action to obtain an artificial head and collect usable test data from oxygen mask mic testing that will enable the committee to add requirements to the standard. This action will be completed prior to the April meeting. A frequency response versus sensitivity performance graph would be an additional and useful outcome of the oxygen mask performance characterization work. Another issue that should be considered by the oxygen mask working group is related to the cord connector flexibility test requirements. The requirements in the current DO-214 standard to not apply in the say way to the oxygen mask microphone cord because the cord is mechanically routed in parallel with the oxygen mask hose. The hose prevents the same kind of torsion and pull forces from being applied to the cord. An appropriate test needs to be defined for the oxygen mask cord and connector. Participants responsible for oxygen mask microphone system work are: Murzeau Frank – Lem Elno Rosier, Julie – Lem Elno Tom Mcdonald - B/E Aerospace Besset, Christophe – Intertechnique Christian Kast – Holmco All other microphones covered by the current standard include specific sections for the type of microphone (e.g. hand mic, boom mic, etc.) . The oxygen mask mic system similarly should be addressed by its own sections within the revised standard. See also, EASA deviation paper is ETSO.DevP.44.pdf below. The EASA deviation paper is ETSO.DevP.44.pdf and will be uploaded on the RTCA sharepoint site for the working group’s review and consideration. Page 6 of 20
RTCA Paper No. 021-13/SC226-010 February 6, 2013 SC226 committee response: The oxygen mask working group should also consider the EASA deviation request related to frequency response modification from the current DO-214 standard requirements. Seventh item of discussion: Discussion “HOT MIC” definition within the standard, Michel Colin, Airbus Michel noted that the standard should define the term “HOT MIC” (e.g. the MIC to CVR audio path through the audio system). The ED112 definition can be used. Michel Collin, Airbus, submitted the following language originating from ED112: Hereunder the definition of Hot-mic from ED 56A: The CVR 'HOT' Microphone: The hot-microphone ensures that, in addition to the recording of the radio transmissions to and from the aircraft, all sounds received by the crew's microphones are recorded continuously irrespective of the position of the audio selector switches. The volume control has no effect on the level of recording of the hot-microphone. A minor interface change provides the hot-microphone feature by summing each crew member's microphone signal with the telephone signal. The CVR itself is not affected by implementation of this concept. And a precision given by ED 112: Each CVR should be installed so as to provide with reference to a timescale, simultaneous recordings of: i. voice communications transmitted from or received in the cockpit by radio, ii. the aural environment of the cockpit, iii. the audio signals received from each boom and mask microphone in use, without interruption, 8th item of discussion: Audio Noise Without Signal and Listening Test during DO-160x Section 8 vibration. Todd Blackstock, AEM, pointed out that DO-143 for Marker Beacons allows a relaxed noise requirement during vibration. Additional vibration test data taken from a system tested by Cobham determined that at some resonant frequencies, noise levels during vibration can reach 30 dB below rated power. Honeywell also reviewed their test data and confirmed similar results from testing they had performed. For audio systems, a noise and listening test should be included because problems with noise have been observed, such as due to microphonics. The noise level can similarly be relaxed from the 50 dB below rated power requirement from Section 2.4 because the ambient acoustic noise background is also elevated during the test, and during normal operation of the system in its operating environment. Thus Page 7 of 20
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SC-226 MEETING MINUTES Working Group JANUARY 14 ... - RTCA

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