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

SC-226 MEETING MINUTES
Working Group
JANUARY 14 to 16, 2013
Gables Enginnering, Coral Gables
RTCA Paper No. 021-13/SC226-010
February 6, 2013
Note: Due to the fact that we cannot verify that the DFO was in attendance for the entire duration of
the committee’s January 14-16 plenary meeting in Coral Gables, Florida, RTCA has decided to recharacterize
the meeting as a Working Group meeting, and not a plenary, to ensure that we adhere to
the Federal Advisory Committee Act.
To ensure that we do not lose all of the hard work that went into the January 14-16 meeting, we will add
an agenda item to the next plenary meeting, scheduled to take place April 15-17, to do a thorough
review of the minutes of the January meeting, and offer anyone a chance to comment on any actions
taken at that meeting.
New Participants
Besset, Christophe - Intertechnique
Tom Mcdonald - B/E Aerospace
Steve Smejka - Thales Avionics
Fraser Mcgibbon - Thales Avionics
Wanpyo Hong - Collier, Hansei University, South Korea
Pascal Hamel - Cobham France
Dan Gauger, Bose
Murzeau Frank – Lem Elno
Rosier, Julie – Lem Elno
Pluviose, Eveillard – Gables
Robert Miller – Gables
Walt Viater – Gables
Rick Robles – Gables
Allan Prince - Cobham
Sophie Bousquet – RTCA (on the phone)
Previous Attendees continuing participants
Michel Colin – Airbus
Don Hamilton – Alto Aviation
Ken Vanderputten – Avtech
Paul Menard – Avtech
Christian Kast – Holmco
Jorg Buchberger – Sennheiser
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Christian Grone – Sennheiser
Anthony Mangiameli – Bose
Gregory Laborde – Cobham (not in attendance)
Francesco Orsino – Gables Engineering
Don Nault – Boeing
Mark Goldberg - Honeywell
Todd Blackstock – AEM
Steven Parker – Bosch Security System
Marchus Schmitz – Becker Avionics (not in attendance)
Greg Sherwood – Garmin (not in attendance)
Greg Frye – FAA (on the phone)
First item of discussion: Pink Noise. Paul Menard - Avtech
Suggestion to add reference to IEC60065 in the definitions section of the standard as a “recommended
definition of pink noise”
As part of the General Test Conditions for audio, IEC60065 section 4.1.6 states “Where relevant, a
standard signal consisting of PINK NOISE, band-limited by a filter whose response conforms to that given
in figure C.1 in annex C.” IEC60065 Figure C.1 from annex C is shown below.
Second item of discussion: RF Susceptibility, Rick Robles - Gables
Gables offered language addressing for Section 20 allowance for special instances where “in-band” RF
threat signals can cause noise beyond the required threshold for the equipment performance similar to
the allowance in Section 2.5.10 and 2.5.11 of the current DO-214 standard.
Honeywell mentioned that they test the threat level to determine that there are no operational failures
or system state changes as a result of the full threat level being applied. DO-214 allows the threat signal
to be lowered to 2V/M when the threat signal generates too much audio noise.
Example: The Category S definition is the ambient RF environment in the aircraft. There already
has been a precedence set by DO160 to use Category S to pass RF MOPS. This should also be the
Category used to pass the signal to noise audio MOPS.
Airbus mentioned that they had an instance where a CAM was made non-functional by a GSM RF signal
installed on the aircraft. ED112 now requires a minimum threat level of 20V/M as a minimum
allowance.
Boeing will discuss a possible solution with Gables and get back to us.
Completed discussion of Gables paper. Proposed language was provided to Boeing to review.
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Third item of discussion: RF Susceptibility test levels and parasitic oscillation definition, Scott Moore -
Jupiter Avionics
The DO-214 Sec 2.5.11.2 Sustained Ambient RF Test (Radiated and Conducted) requires
changes to the frequencies and levels used during the audio noise without signal test. However
there is no clear instruction regarding which modulation to apply during the exposure.
My other suggestion is for 2.8.2.2.1 Audio Frequency Response. It would be beneficial to have a
definition of what a "parasitic oscillation" is, or change the requirement such that a standard and
measurable audio attribute is referred to.
Committee discussion identified that DO-160 includes the specified modulation frequency and level as
well as the RF threat signal levels and frequencies. 20.4 paragraph (e) and 20.5 paragraph (e) both
define the modulation frequency and level.
The committee also agreed that it is true that parasitic oscillation was not well defined.
The definitions section was revised to change Spurious Signals to Spurious/Parasitic Signals.
Committee review of the definitions section found that the existing definition adequately covers the
definition of “parasitic”.
Other sections that referred ambiguously to oscillations in the form of “unwanted” oscillations were
revised to include “parasitic” where applicable.
Fourth item of discussion: ANR performance testing requirements, Anthony Mangiamelli and Dan
Gauger - Bose
Bose offered a paper regarding performance testing of headsets, relative to problems with
characterizing performance around the 1KHz center as is currently done. Using the 1KHz center is found
not effective or consistent and does not reflect human speech perception. A graph offered by Bose
illustrates the actual performance.
Bose proposes requiring a wide band performance test rather than a discrete 1KHz test.
Todd Blackstock – AEM inquired about a concern over cert authorities’ possible perception that the
headset and audio system might be perceived not consistent with one another. A note can be added to
address the equivalency of the 1KHz specified headset to the 1KHz center frequency use to characterize
performance of the audio system.
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Another question was raised concerning whether the graph in the Bose paper takes into account the
female voice. Bose will look into this.
Bose offered to write some proposed language for the standard based on their paper. The other
manufacturers participating agreed with the information proposed. The committee welcomed Bose’
paper.
Boeing and Airbus both agreed that with new language based on the paper by Bose, they will be able to
select amongst varying manufacturer’s ANR headsets and have a consistent way to make a comparison
between them, and thereby more easily certify the headsets for their aircraft without significant testing
as was needed in the past.
Bose also suggested that instead of using power as the input to test the headset, voltage should be used
as active headsets no longer have the same impedance as passive headsets. Input power is less
important when an active circuit is connected in between the input and the speaker. A consistent input
voltage is deemed to have more value for both passive and active applications.
Bose will also get with Sennheiser and Bosch to discuss all aspects of their paper to come to consensus
prior to returning to the next meeting with their recommended language.
They will also address how to insure that ANR headset meet the same DO-160 audio performance
requirements from DO-214 section 2.5 as are required by other microphones.
Participants responsible for headsets (ANR and passive) work are:
Anthony Mangiameli – Bose
Dan Gauger, Bose
Steven Parker – Bosch
Jorg Buchberger – Sennheiser
Christian Grone – Sennheiser
Christian Kast – Holmco
Fifth item of discussion: EASA Deviations
EASA deviation paper ETSO.DevP.52d.pdf (Deviations requests #52 for an ETSO approval for CS-ETSO
applicable to Headsets, Speakers and Aircraft Microphones (ETSO-C57a, C58a) Consultation Paper)
should also be addressed as part of the headset working group’s efforts on how to best measure
sensitivity. Current language in the standard is as follows:
2.3.3.1 Headsets and Handsets
When tested in accordance with the test procedure of subparagraph 2.7.2.1a,
each ear phone shall have a sensitivity of 90 ±5 dB SPL (re: 20 uPa) with
an input power level of 1 mW (RMS). A volume control may be provided to
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meet this requirement.
below 75 dB SPL.
However, it shall not be possible to reduce the level
Language in the EASA deviation paper is as follows:
To allow better harmonisation with the used side tone adjustments industry has received demands from
operators to increase the output sound pressure to values above 95 dB (re: 20 µPa) when providing 1
mW (RMS) to the headset or handset. Today technology allows providing higher sound pressure levels
out of 1 mW (RMS) without producing distortions……..
ETSO-C57a#7 – Headsets and Speakers
Deviate from RTCA DO-214 2.3.3.1 and provide a higher Sound Pressure Level (SPL) of 90 -5/+18 dB
instead of 90 +/- 5 dB SPL (re: 20 µPa) out of 1 mW (RMS) input signal……
Action has been given to the headset working group to complete by April 2013. Proposal based on EASA
deviation paper is to study changing the headphone sensitivity tolerance from +/- 5dB to +8/-5dB. The
working group will study and bring back their recommendation to the group.
6 th item of discussion: Oxygen mask mic performance testing requirements, Murzeau Frank – Lem Elno
and Rosier, Julie – Lem Elno
Discussion around characterizing the performance of oxygen mask microphones while installed in the
oxygen mask. The oxygen mask microphone can be understood to include the mask assembly, the
microphone installed inside the mask assembly, and any circuitry that is included between the output of
the microphone and the audio system. The mask, microphone and circuitry can be called the oxygen
mask microphone system.
Rosier offered a presentation addressing performance of oxygen mask microphones compared to DO-
214. Currently oxygen mask microphones are characterized according to the hand mic test
requirements of DO-214, without the microphone installed in the oxygen mask, and using the same
couplers and equipment.
The problem experienced by audio system designers and installers is that the output of the oxygen mask
mic is often mismatched with other microphones that feed the same system so resistor padding must be
applied in the installation to bring the oxygen mask microphone output level down to the same level as
the other microphones.
An artificial head was shown by Bose which, theoretically, could be used to test the oxygen mic when it
is installed in the mask. But there does not exist any performance data on how the microphone
performed when installed in the mask and therefore, the committee does not yet know how to
performance requirements for the oxygen mask and oxygen mask mic when integrated together.
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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.
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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
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a relaxed noise requirement will not incumber intelligibility. The following language is being added to
section 2.5.5 (c).
(2) Subparagraph 2.4.11.1 - Audio Noise Without Signal
(3) Paragraph 2.4.15 - Listening Test
The equipment shall be subjected to the test conditions, as specified
in RTCA/DO-160x, Section 8 .0. Exception: The following test level shall
apply:
For Audio Noise Without Signal, when tested in accordance with the test
procedures in subparagraph 2.8.2.11.1, the level of the noise output of the
system shall be at least 30 dB below the rated output of the system.
9th item of discussion: EASA deviations
Deviations reviewed:
EASA Deviation ETSO.DevP.17.pdf (Deviations requests #17 for an ETSO approval for CS-ETSO applicable
to C57a (Headsets and Speakers) Consultation Paper)
EUROCAE ED-18 specifies:
Using the resistor substitution method, the equipment impedance at 1000 Hz shall be
within ± 20% of the manufacturer’s rated impedance, which shall be between the limits
of 150 Ωand 600 Ω
Note
Some general aviation avionics equipment may require the use of headsets with only
600 Ω impedance.
Use of lower impedance headsets could result in damage to such avionics 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 only 600 Ω headsets. If in doubt, consult the
avionics equipment manufacturer.”
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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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Due to the reduced strains and weight of the earpiece, Therefore the maximum pulling load of
1.0 kg shall be applicable for the earpiece – cable interface.
EASA deviation ETSO.DevP.56c.pdf Deviation request #56 for an ETSO approval for CS-ETSO applicable
to Aircraft Microphones (ETSO- C58a) Consultation Paper – Christian Kast, Holmco
Added section 2.2.2.3 to address the EASA deviation allowing 3.5dB output increase instead of 5dB
required for all other microphones based on testing done by Holmco and submitted and approved by
EASA.
2.2.2.3 Handset Microphone
When tested in accordance with the test procedure in subparagraph 2.6.2.3, the
total harmonic distortion contributed by the microphone shall not exceed five
percent over the frequency range of 350 to 6000 Hz at a sound pressure input of
114 dB SPL (re: 20 pPa). Increasing the sound pressure input by 6 dB must yield
an output increase of at least 3.5 dB.
DO-160x references issues: Todd Blackstock – AEM
We have previously changed all references to DO-160C to DO-160x. Todd Blackstock has re-reviewed
the edited standard and found additional references to specific subparagraphs within DO-160C that are
still referenced. Specific subparagraph numbers within DO-160C should not be referenced in the
revised standard because DO-160 is revised so often and specific subparagraph numbers could change.
The consensus is that we can use the section title and major section number (e.g. 16.0) from DO-160 as
a more reliable reference since these are less likely to change as new revisions of DO-160 are produced
in the future. Additional references within the standard, to specific categories from DO-160 need to be
reviewed and edited as appropriate as well. Highlighted below.
2.4.11.1 Audio Noise Without Signal
When tested in accordance with the test procedures in subparagraph 2.8.2.11.1,
the level of the noise output of the system shall be at least 50 dB below the
rated output of the system for Category A and B and 60 dB for Category Z
(RTCA/DO-160x Definitions, Subsection 19.2).
2.5.1 Temperature and Altitude Tests
RTCA/DO-160x contains several temperature and altitude test procedures that
are specified according to equipment category. These categories are included
in Subsection 4.3 of RTCA/DO-160x. The following subparagraphs
contain the applicable test conditions specified in Section 4.0 of RTCA/DO-
160x.
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2.5.6 Magnetic Effect Test
a. Aircraft Microphones (except Carbon):
During the test, the following requirements shall be met:
The requirements of the appropriate RTCA/DO-160x category.
It is recommended that microphones intended for use in the cockpit,
should meet the requirements of categories Z and A. It is strongly recommended
that a cautionary note citing possible effects to magnetic compasses, be
packed with microphones meeting requirements other than Class Z.
b. Aircraft Headsets, Handsets and Loudspeakers:
During the test, the following requirements shall be met:
The requirements of the appropriate RTCA/DO-160x
category.
It is recommended that headsets and handsets intended for use in
the cockpit, should meet the requirements of categories Z and A.
It is strongly recommended that a cautionary note citing possible
effects to magnetic compasses, be packed with headsets and handsets
meeting requirements other than Class Z.
STANDARD
NORMAL OPERATING CONDITIONS
MINIMUM SUPPLY
VOLTAGE
EMERGENCY SUPPLY
VOLTAGE
Rated Power
-3 dB
REF: 0 dB = Rated Power
in Paragraph 2.4.2
-6 dB
REF: 0 dB = Rated
Power in Paragraph 2.4.2
Distortion 20% 30%
No Signal Noise
-50 dB Cat. A & B
-60 dB Cat. Z
-40 dB Cat. A & B
-40 dB Cat. Z
Listening Test Intelligible Intelligible
TABLE 2-1 TABULATION OF REQUIREMENTS FOR POWER INPUT
TEST
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Todd Blackstock reviewed the categories called out in the standard and determined that the categories are still
applicable. Section 1.8 has been revised as follows:
1.8 Test Procedures
The test procedures…………
a. Environmental Tests
Environmental test requirements are specified in Subsection 2.5. The
procedures and their associated limit requirements are intended to
provide a laboratory means of determining the electrical and mechanical
performance of the equipment under environmental conditions expected to
be encountered in actual operations. Unless otherwise specified, the
environmental conditions and test procedures contained in RTCA/DO-
160x, whereas DO-160x refers to the latest version of DO-160 or as
previously agreed with the administrator, Environmental Conditions and
Test Procedures for Airborne Equipment, will be used to demonstrate
equipment compliance. Within section 2.5 of this document, the relevant
subsection titles are from DO-160G and referred to in each subsection of
section 2.5. In the event that future revisions of DO-160x result with the
referenced subsections being renamed, the closest equivalent subsection
should be used for compliance with section 2.5 of this document.
Discussion of microphone performance testing under DO-160 test conditions:
Many tests require performance testing under DO-160 conditions after the test.
Altitude was raised as a problem. Members of the committee do not know of any artificial voice
equipment that is calibrated under altitude conditions so the source of the signal can be said to have
unknown performance quality under the test conditions.
DO-214 requires tests to be performed during exposure to altitude. The question posed, is how to
insure that the performance is known and correct under the test condition.
2.5.1.4 Altitude Tests
The equipment shall be subjected to the test conditions as specified
in RTCA/DO-160x, Section 4.0
a. Aircraft Microphones (except Carbon):
During the test, the following requirements shall be met within ±6
dB: (1) Paragraph 2.2.1 Frequency Response
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(2) Paragraph 2.2.3 Sensitivity
Sennheiser offered to check with company physicists to determine what the theoretical performance of
their microphones under low pressure conditions would be expected to be.
B/E Aerospace can coordinate test activities to try to determine what the effect on the acoustic source
and the microphone under test would be under altitude conditions.
The same issues pertain to Temperature and Temperature Variation except that the test specifically
refers to the microphone preamplifier (independently of the microphone?). The committee had a range
of interpretations.
2.5.2 Temperature Variation Test
The equipment shall be subjected to the test conditions as specified
in RTCA/DO-160x, Section 5.0.
a. Aircraft Microphones (Except Carbon):
The microphone preamplifier, as a component of the microphone
assembly shall be subjected to this test. During the test, the following
requirements shall be met:
(1) Subparagraph 2.2.2.1 Distortion Characteristics
(2) Subparagraph 2.2.3.1 Sensitivity
Bosch offered to check with the test equipment manufacturer to determine what the performance of
the artificial voice would be expected to be under temperature and temperature variation test
conditions.
Additional question: Why are the Aircraft Headsets, Handsets and Loudspeakers excluded from the
temperature variation test. Bosch, Sennheiser and Bose were asked to check with their engineering
departments to determine a valid reason.
Discussion on RF Interference and 2V/M relaxed noise allowance in Section 2.5.11.
Another issue is the title of “sustained ambient” and “transient”. These do not align with the current
version of DO-160.
The “sustained ambient” and “transient” sections should be combined into one.
Radio Frequency Susceptibility Test (Radiated and Conducted)
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This section is partitioned into two subsections. The first deals with short duration exposure to
transient radiated fields. The second deals with sustained ambient lower intensity radiated
fields. The requirements of both subsections must be met.
Transient RF Test (Radiated and Conducted)
The equipment shall be subjected to
RTCA/DO-160x, Section 20.0.
the test conditions, as specified in
a. Aircraft Microphones (except Carbon):
During the test, the following requirements shall be met:
The recovered modulation shall not be more than 10 mV RMS.
NOTE:
The microphone should survive the test, fully recover
following the test, and should not cause any unsafe
condition in system operation during the test.
b. Aircraft Headsets, Handsets and Loudspeakers:
NOTE: Any headset or handset containing active components should
not generate acoustic levels that may interfere with safe
operation of the aircraft.
c. Audio System:
During the test, the following requirements shall be
met: Paragraph 2.4.15 - Listening Test
NOTE: The test shall not cause any interruption in communication
as determined by the listening test. Degradation of signal
quality is acceptable as long as the signal remains adequate
for communications. Furthermore, system state changes
(such as system resets, configuration changes, volume level
changes, etc.) shall not occur.
2.5.11.2 Sustained Ambient RF Test (Radiated and Conducted)
The equipment shall be subjected to the test conditions, as specified
in RTCA/DO-160x, Section 20.0. Exception: The following test levels and
frequencies shall apply:
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For Radiated Susceptibility: The level shall be 2 V/m at the frequency range
specified within the applicable category in DO-160x.
Note: DO-307 covers Radiated RF Interference considerations for
Transmitting Portable Electronic Devices (PEDs). RF Interference from PEDs
devices can interfere with functions of the audio system. Audio System
components are only exposed to PEDs RF Interference when the Audio System
component is located in an area of the aircraft near the PEDs devices and when
there is no metal shielding between the audio system component and the PEDs
devices. As a result, it is reasonable for only the exposed audio equipment to be
tested according to the requirements of DO-307. Additionally, when equipment
is mounted so that a portion of the equipment is shielded, it is reasonable for
only the exposed side(s) of the audio equipment to be exposed during the PEDs
RF Interference testing. An analysis should be used to describe the rationale
for the manner in which the equipment under test is exposed.
Discussion of problems experienced by members of the committee with regard to current test
requirements calling for the conducted RF frequency sweep to start at 10KHz.
Experience of the participants has found that even when the 10KHz RF signal is applied with no
modulation, it can often be heard over the audio system. 10KHz is very close to the audio frequency
band of interest for the audio system. The audio system is typically composed of a large number audio
inputs and outputs, all of which must be filtered to remove RF. However, with the RF starting
frequency so close to the audio frequency band, the filters must be more effective, more complex,
require more components, and occupy more space within the equipment enclosure in order to be
effective enough to remove 10 KHz RF noise. As a practical matter, such a design will be
mathematically less reliable, and the committee questions why the RF frequency should start at such a
low frequency when there are no sources of this type on board the aircraft. The consensus was that
the starting frequency should start at a frequency just beyond the maximum audio frequency band
discernible by human hearing (e.g. >20 KHz). 24 KHz was chosen as the new starting frequency. The
language in the standard was edited as follows for conducted RF susceptibility testing.
For Conducted Susceptibility: The level shall be 3 mA (2 V/m) from 500 kHz to
400 MHz, and from 500 kHz to 24 kHz shall fall at the rate of 6 dB per octave (20 dB per
decade).
Don Nault, Boeing took the action to check with his compliance personnel at Boeing to determine if the note is
acceptable.
Discussion on fire protection. TSO-C57a and TSO-C58a used to include a requirement similar to as follows from
DO-214 but no longer do and this sometimes causes problems for Boeing when equipment is not tested to Part 25
Appendix F.
2.1.4 Fire Protection
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RTCA Paper No. 021-13/SC226-010
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All materials used shall be self-extinguishing except for small parts (such
as knobs, fasteners, seals, grommets and small electrical parts) that would not
contri bute significantly to the propagation of a fire.
NOTE: One means of showing compliance is contained in Federal
Aviation Regulations (FAR), Part 25, Appendix F.
The committee decided that there are many means used (and allowed by the note above) to comply
with the fire protection requirement. The section should be remain worded as is.
Discussion of headsets, handsets and loudspeakers that are connected to aircraft power. The
committee identified the subsections within section 2.5 of the standard that will have to include new
performance requirements for headsets, handsets and loudspeakers that are connected to aircraft
power. The effected sections have been tagged “TBD” in the draft standard as noted below. The output
of the headset working group’s actions should provide guidance of what performance tests are required
for the effected sections.
Applicable to headsets, handsets and loudspeakers utilizing aircraft power,
During the test, the following requirements as modified in Table 2-1 shall be met: TBD
A previous temporary comment was included in the draft standard left open the text of the test
procedure for the PTT delay test. A reference was added to new paragraph 2.8.2.13.3 within 2.4.13.3
added during a previous committee meeting.
2.4.13.3 Push to Talk (PTT) Delay
From the time that the PTT input to the system is activated, the system shall produce a PTT at the
system output within a period of 100 milliseconds when tested in accordance…….. with
subparagraph 2.8.2.13.3
Section 2.8.2.13.3 is also now added:
2.8.2.13.3 Push to Talk (PTT) Delay
a. Apply a 0.1 Hz square wave signal from an open/ground signal souce to the PTT input of the
equipment while monitoring the PTT input signal with an oscilloscope.
b. Monitor the PTT output of the equipment with a second channel of the oscilloscope and
measure the time difference between the PTT input and PTT output signals.
c. Repeat for dissimilar input/output combinations.
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Discussion of DO-160x, DO-178x and addition of reference to DO-254. Need to address adding a
reference to DO-254 within the standard and as follows:
Remove ‘x’ from DO-160 and DO-178 references within the draft standard to make the references
cleaner. Edit the DO-160 and add reference to DO-178 and DO-254 to generic revision reference note to
reflect removal of ‘x’. The note could be stated to reference the base document number with no rev.
Discussion with headset manufactures pointed out that 300 ohm single sided headsets exist presently.
Section 1.5.5(b) needs to include the following medium impedance headset impedance:
Medium Impedance Headset
300 Ω ± 20% nominal across the frequency range.
All sections referencing headset impedances need to be harmonized to insure that they all reflect the
same list of impedances, headset output loads and tolerance callouts where applicable.
There are also still references to 150 to 600 ohms. 300 ohm medium impedance headsets (mono or
stereo) fit between 150 and 600 ohms. But these need to be revised to also include 8 ohm low
impedance.
Also need to review microphone impedances and tolerances and insure they are harmonized throughout
the standard. 1.5.3 in DO-214 still references 250mV, whereas 2.2.3 now references 400mV with 114dB
SPL input to be consistent with ARINC538. 400mV with 114dB is the preferred specification.
Discussion about problems managing the large number of headset impedances available on the market.
Consensus was that standardizing on a single impedance headset is desirable and that a note within the
standard would be helpful to guide industry in this direction in the future.
Proposed language: It is highly desirable to for future applications to standardize on 150
ohm mono (300 ohm stereo) headsets
Pascal Hamel - Cobham France, has the action to perform a study of the impact of referencing a
preferred impedance from the choices of 8 ohms, 150 ohms, 300 ohms or 600 ohms within the
standard.
Sennheiser offered the following comparative headset impedance information from various
manufacturers for reference.
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RTCA Paper No. 021-13/SC226-010
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DO 214 2.3.4.1 150 Ohm 600 Ohm
ARINC 535A 550 Ohm 650 Ohm
Manufacturer Application 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13
Holmberg Commercial 550 Ohm
Holmberg Commercial 560 Ohm
Holmberg Commercial 570 Ohm
Sennheiser HMEC 26 Commercial 600 Ohm 1200 Ohm
Sennheiser HMEC 46 Commercial 600 Ohm 1200 Ohm
Telex Airman 750 Commercial 150 Ohm 300 Ohm 600 Ohm
Telex Airman 850 Commercial 150 Ohm 300 Ohm 600 Ohm
Telex Ascend Commercial 600 Ohm
Plantronics MS 260 Commercial 600 Ohm
Beyerdynamic HS400 GA 210 Ohm 270 Ohm
Beyerdynamic HS800 GA 260 Ohm 560 Ohm
Bose A 20 GA 160 Ohm 320 Ohm
Bose X GA 160 Ohm 320 Ohm
Peltor 8003 GA 165 Ohm 330 Ohm
Peltor 8006 GA 165 Ohm 330 Ohm
S1 DIGITAL GA 180 Ohm 360 Ohm
S1 PASSIVE GA 140 Ohm 280 Ohm
Sennheiser HMEC 460 GA 400 Ohm 600 Ohm
Sennheiser HMEC 350 GA 300 Ohm 600 Ohm
Sennheiser HME 110 GA 150 Ohm 300 Ohm
Sennheiser HME 95 GA 225 Ohm 300 Ohm
Telex 30XT GA 150 Ohm 300 Ohm
Telex 50D GA 150 Ohm 300 Ohm
David Clark X11 GA 225 Ohm 450 Ohm
David Clark H10-13.4 GA 150 Ohm
David Clark H10-13X GA 150 Ohm 300 Ohm
Peltor 8103 Helicopter 16 Ohm 32 Ohm
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RTCA Paper No. 021-13/SC226-010
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3.2.2Acoustic Output
The acoustic output of the headset should be 100 dB, ref. 0.0002 dynes per square centimeter per 1.0
milliwatt (0.5 mW per earphone) in the frequency range of 300 to 4000 Hz within the following limits:
300 Hz ± 3 dB ref. 100 dB per 0.5 mW
1000 Hz ± 1.5 dB
4000 Hz ± 3 dB
8000 Hz ± 10 dB or more
Note: 100 dB per 0.5 mW is equivalent to 20 dynes per square
centimeter per 0.5 mW, or 52 dynes per square cenitmeter
per 1 volt.
COMMENTARY
The headset acoustic output should not exceed 100 dB per
milliwatt because a desired signal-to-noise ratio of 46 dB requires
that the system noise hum level be suppressed to a value below 4
millivolts.
Discussion of headset connectors. The committee discussed the benefits of the XLR-5 versus the XLR-7
connector. The problem with XLR-5 is that it has too few pins to include DC-. As a result, DC – is often
shared with the MIC return causing conducted audio frequency (400 Hz commonly) noise problems in
the ANR headset audio.
XLR-7 provides additional pins, not only for DC – but also includes a pin that can be used for headset
stereo right. Headset stereo left can be dual use with headset mono HI.
The Sennheiser white paper submitted at the July 2012 SC226 DO-214 committee meeting was
referenced. The following language is proposed for the standard.
3.3Plug (from ARINC535B draft)
A single plug and cord should be provided for the microphone and headset. The plug should be an XLR-
7 straight plug with the following pin connections:
Pin 1 – Headset Hi/Left
Pin 2 – Headset Lo
Pin 3 – Mic pre-amp Hi
Pin 4 – Mic pre-amp Lo
Pin 5 - DC+
Pin 6 - DC-
Pin 7 - Headset Hi/Right
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RTCA Paper No. 021-13/SC226-010
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The headset working group will need to analyze power supply input performance, current and any other
parameters applicable to the active headset power pins and provide a recommendation to the
committee.
Future meeting dates:
July week of 15 th -19 th (RTCA 15 th - 17 th and then ARINC 18 th and 19 th ) and October 1 st -4 th (RTCA 1 st and
2 nd and then ARINC 3 rd and 4 th ).
Proposed locations would be: April in DC, July in DC (or to be determined), October in DC (or to be
determined).
A suggestion was raised, for better European participation, that we try to hold a meeting in Germany in
July. Sophie from RTCA will check to see if this is a possibility.
ARINC meetings that follow SC-226 meetings in Berlin Germany.
Sophie from RTCA suggested that we release the document 45 days prior to PMC in December.
Early October SC226 meeting will be held to finalize changes following FRAC (TOR says completion end
of September (early October suffices).
Need to discuss publication date for the new TSO at next session.
Detailed agenda will need to be completed and posted on the share point site for completion of
remaining activities in April, July, and October.
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