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

RTCA Paper No. 021-13/SC226-010
February 6, 2013
Industry:
Some aircraft manufacturers require headsets with impedance that shall be between the
limits of 8 Ω and 32 Ω± 20%.
An equivalent level of safety is provided limiting the use of headsets with low impedance
in the aircraft or helicopters that require low impedance.
SC226 committee response:
The committee has addressed the use of 8 ohm and 50 ohm (representative of multiple 150 ohm)
headsets connected in parallel. 8 ohm is now considered within the revised standard as “low
impedance”, 600 ohm is now considered “high impedance” and 150 ohm is considered “commercial
aviation impedance” headsets.
The committee knows of no application of 32 ohm headsets being used in cockpit communication
applications. 32 ohm headsets that the committee is aware of are typically consumer style headsets
such as those used in the airline passenger cabin for music listening purposes, or those sold on the
consumer market for IPOD music players. As such, 32 ohm headsets are not deemed appropriate for
coverage by the revised standards.
On the subject of damage to equipment occurring due to the use of low impedance headsets on a
system intended for high impedance headsets, the committee considers that the standard also has a
requirement for a short circuit test that is intended to insure the equipment is protected against
damage due to low impedances being inadvertently connected. However, the committee also considers
that there could be legacy equipment still in use within aircraft that may not have been required to
meet the short circuit test contained in previous standard DO-170 or current standard DO-214 and as
such, the note below DO-214 section 2.3.5.2 still applies. Note as follows:
Some general aviation avionics equipment may require the use of headsets with 600 Ω impedance only. Use of lower
impedance headsets could result in damage to such equipment. Therefore, headsets which have an earphone circuit impedance
other than 600 Ω ±20% shall include in their installation instructions a caution stating the following: "Damage could occur
to avionics equipment by the use of these headsets if the equipment was manufactured for use with 600 Ω headsets only-if in
doubt, consult the avionics equipment manufacturer."
EASA deviation ETSO.DevP.27.pdf Deviations requests ETSO.Dev.P027 for an ETSO approval for CS-
ETSO applicable to Headset including Microphone (ETSO-C57a, C58a) Consultation Paper
SC226 committee response:
To address headset cord connector pull out the following note has been added to the standard section
2.2.8.3 and 2.3.8.4:
Note: The earpiece-cord fastening for the headset will be subject to less amount of steady pull
as the headset is not fixed at the head and the headset is not connected to a fixed mounted panel.
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