Civil Aviation Order 103.25 Instrument 2007 (Cth)
I, WILLIAM BRUCE BYRON, Director of Aviation Safety, on behalf of CASA, make this instrument under subregulation 21A (1) of the Civil Aviation Regulations 1988.
[Signed Bruce Byron]
Bruce Byron
Director of Aviation Safety and
Chief Executive Officer
17 December 2007
Civil Aviation Order 103.25 Instrument 2007
1 Name of instrument
This instrument is the Civil Aviation Order 103.25 Instrument 2007.
2 Commencement
This instrument commences on the day after it is registered.
3 New Civil Aviation Order 103.25
Civil Aviation Order 103.25 is repealed and a new Civil Aviation Order 103.25 substituted as set out in Schedule 1.
Schedule 1 Civil Aviation Order 103.25
Equipment standards — VHF communications receiving equipment
This Order is to be read in conjunction with Order 103.21.
1 Application
1.1 This Civil Aviation Order specifies standards for airborne communications receiving equipment operating within the frequency range from 117.975 to 137 MHz.
1.2 These standards apply to the approval of equipment for use in Australian registered aircraft for the purpose of intercommunication with the aeronautical mobile radio service.
Note For international operations, some minimum performance requirements may not be adequate.
2 Design requirements
2.1 The equipment must be designed for the reception of A3 (telephony) emissions.
2.2 The frequency range and number of channels must be adequate for the intended operational purpose of the equipment.
Note Australian domestic aeromobile VHF communications channels are allocated from 25 kHz increments within the range 117.975 to 137 MHz.
2.3 Not more than 2 controls must be used to accomplish frequency selection and tuning.
These controls must switch into operation pre-set frequency determining circuits.
Note Continuously tunable receivers will not be approved.
2.4 The receiver must provide for transmit-receive change-over from a single press-to-transmit switch. The 1 action must accomplish all necessary switching functions, including loud speaker muting (if applicable) during transmit.
2.5 Audio level controls must be connected in such a manner that variation of the controls will not cause a significant change in audio output level of other equipment with which its audio output may be paralleled.
2.6 Controls not intended for use during flight must not be readily accessible to the flight crew.
2.7 All indicators, controls and test points must be clearly marked or readily identifiable as follows:
(a) indicators and controls for in-flight operation must be marked in English symbols;
(b) indicators, controls and test points for maintenance adjustments to installed equipment must be marked in English or recognised technical symbols;
(c) controls and test points used only during maintenance at the test bench must be identifiable by means of suitable markings or other means of providing unambiguous identification, e.g. overlays, photographs.
2.8 The equipment must be designed so that any possibility of incorrect mating of connectors is minimised. Plugs and sockets without positive means to prevent incorrect mating must be suitably marked or readily identifiable with their function or circuit reference.
2.9 The equipment must be so designed that the possibility of electric shock to passengers or crew is negligible.
2.10 The equipment must be so constructed that the normal methods of mounting and the application of vibration and shock under the most severe conditions likely to be encountered by the equipment will not cause detuning or other malfunctions to occur or otherwise damage the equipment.
2.11 The equipment must be designed so that the rating of each component, with appropriate derating, is not exceeded in any localised component environment which may occur during operation of the equipment in any over-all environment implied by its classification.
2.12 The attachment of components and the restraint of plug-in components, adjustment and tuning devices must be adequate to ensure their security and performance of adjustment under the vibration conditions within which the equipment may be operated.
2.13 The performance characteristics of the equipment must be unaffected by operation of panel and indicator lamps incorporated in the equipment.
Note It is recommended that lamps be fitted with a dimming device or provision made for their connection into a suitable dimming circuit.
3 Conditions of test
3.1 Compliance with this Civil Aviation Order must be substantiated by tests conducted on 1 or more sets of equipment to the extent appropriate to the desired classification.
Note 1 The Director may allow some departure from certain individual requirements provided that, in his opinion, overall performance is consistent with the intended purpose of the equipment and is generally satisfactory, throughout the range of environmental conditions mentioned in this Order.
Note 2 The Director may require additional tests to be conducted if particular designs or performance characteristics appear to warrant special assessment.
3.2 During, and subsequent to the application of the specified tests, the equipment must not exhibit evidence of any condition which would be detrimental to its continued satisfactory performance.
3.3 Unless otherwise mentioned or required, tests must be conducted under room ambient conditions.
Note
Room ambient conditions should be:
atmospheric pressure — 810 to 1050 mb or 24 to 31 inches Hg;
air temperature — +10 to +40°C;
relative humidity — less than 85%.
3.4 Unless otherwise mentioned or required, the equipment must be operated at normal rated power supply voltage and frequency. Variations up to ± 2% of voltage and ± 2% of frequency will be accepted.
Note 1 Normal rated voltages and frequencies are those specified by the manufacturer for continuous or stated duty cycle operation of the equipment. Usual ratings will be 13.75 or 27.5 volts for DC and 115 volts at 400 Hz for ac operated equipment.
Note 2 For equipment designed to operate on a variable frequency ac supply, the terms “selected test frequency” and “critical test frequency” should be used and noted in the test reports.
3.5 The input signal level must be interpreted as the “open circuit” voltage (EMF) of the signal source. The signal source output impedance must comprise a resistance within 10% and a reactance of not more than 10% of the characteristic impedance of the transmission line for which the receiver is designed. The input signal level specified in this Equipment Standard are for receivers designed for a transmission line having a nominal characteristic impedance of 52 ohms. In the case of a receiver designed for a transmission line having a nominal characteristic impedance other than 52 ohms, the input signal level must be computed according to the following equation:
E2 =
where E2 is the input signal level to be used for a receiver designed for a transmission line having a nominal characteristic impedance other than 52 ohms.
E1 is the applicable input signal level.
R2 is the nominal characteristic impedance of the transmission line for which the receiver is designed.
3.6 Where a voltage level at radio frequency (other than an input signal level) is specified, it must be interpreted as the voltage actually occurring between the points stated, or the point and equipment frame, as appropriate.
3.7 Unless otherwise agreed by the Director, equipment covered by these Equipment Standards must be capable of continuous operation.
3.8 Accepted test procedures must be used for the conduct of the performance tests required by these Equipment Standards. Unless otherwise agreed by the Director, the same procedures must be used for the conduct of similar tests under environmental, low voltage and normal test conditions.
Note Suggested procedures are contained in Appendix 1.
3.9 Evidence that test equipment is properly calibrated and checked must be made available at the Director’s request.
3.10 Minor modifications to correct deficiencies noted as a result of the tests may be made at any stage of the tests providing that such tests as the Director considers necessary are repeated.
Note Results of repeated tests should be identifiable with the specific modification.
4 Minimum performance requirements under normal test conditions
4.1 Sensitivity
With the receiver squelch circuits disabled, the level of an input signal, modulated 30% at 1 000 Hz, required to obtain a signal-plus-noise to noise ratio of 6 dB must not exceed:
5 5 10 10 microvolts for rating I L2 L1 V
Note Signal-plus-noise to noise ratio is the ratio of the output produced by carrier plus modulation to that with carrier only.
4.2 Audio output
The audio output capability at an input signal level of 20 microvolts modulated 30% at 1 000 Hz must be not less than the rated output power published by the manufacturer.
Note To ensure satisfactory performance in a wide variety of installations, an audio output capability nor less than 50 milliwatts for the headset output circuit and 3 watts for the speaker output circuit (if provided) is recommended.
4.3 Distortion
With input signal levels from 50 microvolts to 10 millivolts modulated 85% at frequencies from 350 to 2 000 Hz and the audio output control set to produce rated output at 1 000 Hz, the total harmonic distortion must not exceed 25%.
4.4 Audio frequency response
The overall audio frequency response must be such as to provide clearly intelligible reception of any normal human speaking voice and attenuation of those frequencies which may detract from, or do not significantly contribute to, intelligibility.
Note Qualitative assessment of audio frequency response may be used until suitable standards are determined for all components of communications systems. The audio frequency response of airborne receivers will be generally acceptable if the output varies by not more than 6 dB as the modulating frequency of a constant level input signal is varied over the range from 350 to 2 500 Hz and the response attenuated above 3 000 Hz. It has been found desirable to attenuate the response at 7 000 Hz to 20 dB or more below that at 1 000 Hz.
4.5 Automatic gain control
The audio output must not vary more than:
6 10 13 13 dB as the input signal is varied from 10 10 20 20 microvolts to 100 microvolts for ratings I L2 L1 V
4.6 Blocking
There must be no evidence of the receiver blocking or significant degradation of output intelligibility when the input signal level is increased to 200 millivolts.
4.7 Paralysis
When a signal of 200 millivolts at the receiver tuned frequency, applied to the antenna terminal, is suddenly reduced to 10 microvolts modulated 30% at 1 000 Hz, the output of the receiver must, within 1 second, return to within 3 dB of the normal steady output obtained with the 10 microvolt signal.
4.8 Manual gain control
The manual gain control must be capable of varying the output of the receiver by at least 24 dB with any input signal level from 20 microvolts to 50 millivolts.
Note A greater range of control is desirable for receivers with high output capability.
4.9 Squelch control
This requirement applies only to equipment for which an I or L rating is desired.
The range of any control intended for in-flight adjustments of a carrier operated squelch circuit must be so limited that the receiver output cannot be muted with any input signal level exceeding 30 microvolts.
4.10 Frequency stability
Stability of the receiver frequency determining circuits must be such that the selectivity requirement expressed in subparagraph 4.11.1 can be met.
Note The received centre frequency should remain within 0.01% of the assigned channel frequency under any combination of environmental conditions implied by the equipment classification.
4.11 Selectivity
4.11.1 The level of an input signal required to produce constant audio output must not vary more than 6 dB when its frequency is varied above and below the assigned channel frequency by 7 kHz plus the magnitude of the maximum departure of receiver centre frequency from the assigned channel frequency under any combination of environmental conditions implied by the equipment classification.
Note The frequency range for this test may be taken as:
for a receiver centre ± 14 20 27 kHz frequency stability of ± 0.005 0.01 0.015 %
4.12 Spurious responses
Over the frequency range from 190 kHz to 1 200 MHz, excluding the band within 80 kHz of the assigned channel frequency to which the receiver is tuned, the response of the receiver must be at least 60 dB (for ratings I and L2) or at least 40 dB (for ratings Ll and V) below that at the assigned channel frequency.
4.13 Cross modulation
This requirement applies only to equipment for which an I rating is desired.
The receiver output due to cross modulation of a desired signal (unmodulated) by an interfering signal (modulated 30% at 1 000 Hz) must be at least 10 dB less than the output due to the desired signal (when modulated) alone at the conditions specified below:
Desired signal Interfering signal (a) Level
Frequency
20 microvolts through to 500 microvolts
At receiver selected frequency
10 millivolts
At 25 kHz steps from 108 to 137 MHz excluding the desired signal frequency
(b) Level
Frequency
As in (a) above
As in (a) above
0.2 volt
200 kHz to 108 MHz
Refer to Appendix 1 for suggested test procedure.
4.14 Spurious emissions
Note 1 Equipment which complies with the requirements for either Category A or B equipment specified in RTCA DO-186 or later amendment will be taken to comply with this paragraph.
Note 2 The emission of spurious radio frequency energy of a transient nature resulting from the manual operation of switches, but not including emissions from circuits operating as a result of that operation, may exceed the limits mentioned in this paragraph if its duration does not exceed 1 second.
4.14.1 Emissions from antenna
The power of any spurious emission present at the antenna terminal on any discrete frequency between 190 kHz and 1 200 MHz must not exceed 1 nanowatt (for ratings I and L) or 20 nanowatts (for rating V) into a resistive load equivalent to the nominal antenna impedance of the receiver.
4.14.2 Emissions from interwiring
This requirement applies only to equipment for which an I rating is desired.
Unwanted radio frequency energy on any cable must be of such level, or must be contained in such manner, that the level of signals on discrete frequencies from 190 kHz to 1 200 MHz induced in another cable run with it does not exceed 1 000 microvolts. (Refer to Appendix 1 for suggested test procedure.)
Note Although this requirement does not apply to receivers with L or V ratings, a similar standard is desirable. Particular attention should be given to minimising spurious emissions within the frequency ranges from 190 kHz to 20 MHz and 117.975 to 137 MHz in order to provide reasonable assurance that mutual interference limits, mentioned in other Civil Aviation Orders, can be met. Transistorised inverters in power supply circuits are frequently responsible for unacceptable emissions.
4.15 Channel selection time
The maximum time for the equipment to change from 1 channel to any other must not exceed 10 seconds.
4.16 Desensitisation
This requirement applies to equipment for which an I or L rating is desired.
The output of the receiver with an input signal at a level of 20 microvolts modulated 30% at 1 000 Hz must not decrease by more than 10 dB in the presence of an unmodulated interfering signal:
(a) having a level of 10 millivolts and a frequency between 100 and 146 MHz, but excluding frequencies within 0.1 MHz of the desired channel frequency; and
(b) having a level of 200 millivolts and a frequency between 190 kHz and 1 200 MHz, but excluding the range from 100 to 146 MHz, and discrete spurious response frequencies. At spurious response frequencies, the interfering signal must have a level of 10 millivolts.
4.17 Audio output regulation
The manufacturer must declare the effect of variation of audio load impedance on audio output power or voltage.
Note Although no specific values of acceptability are set down for this requirement, the information is necessary to the design and approval of aircraft audio installations. The information should cover load impedance variations from 0.25 to 2RL for headphone circuits and 0.5RL for speaker circuits.
4.18 RF input impedance
This requirement applies to equipment for which an I or L rating is required.
&nb sp; Over the frequency range for which the receiver is designed, the VSWR produced on the antenna transmission line by the receiver must not exceed 3:1.
4.19 Operation of mechanical devices
Mechanical devices must perform their intended function. Marginal operation must be avoided.
4.20 Variation of primary power frequency
The equipment must comply with this Equipment Standard when the primary power frequency is varied throughout the range for which the equipment has been designed. For equipment designed to operate from a nominally constant frequency supply, it must be assumed that the frequency will vary by at least ± 5%.
4.21 Application of conducted voltage transients
This requirement applies only to equipment for which an I rating is desired.
Note 1 Although specified for I rating equipment only, it is desired that this requirement be applied, where practicable, to all equipment, especially that which incorporates solid state devices susceptible to damage by voltage transients.
Note 2 This requirement is expressed in this interim form pending further investigation of the magnitude and effects of aircraft electrical system voltage transients.
4.21.1 Intermittent transients
After application of intermittent transients as specified in RTCA DO-186 or later amendment, the equipment must not exhibit evidence of damage and must continue to function without degradation.
4.21.2 Repetitive transients
When the equipment is subjected to the repetitive transients test specified in RTCA DO-186 or later amendment, the audio output of the receiver must be not more than 1.5 dB below that mentioned in paragraph 4.2 of this Order.
4.22 Conducted and radiated interference susceptibility
These requirements apply only to equipment for which an I rating is desired.
Note Although these requirements do not apply to equipment with L or V ratings, a similar standard is desirable, especially for the former, in order to provide reasonable assurance that mutual interference limits, mentioned in other Civil Aviation Orders, can be met.
4.22.1 Conducted audio frequencies
The signal-plus-noise to noise ratio of the receiver output must be not less than 25 dB (at rated output) over the input signal level range from 100 microvolts to 10 millivolts when the equipment is subjected to the test specified in RTCA DO-186 or later amendment.
4.22.2 Audio frequency magnetic fields
The signal-plus-noise ratio of the receiver output must be not less than 25 dB (at rated output) over the input signal level range from 100 microvolts to 10 millivolts when the equipment is subjected to the test specified in RTCA DO-186 or later amendment.
4.22.3 Radio frequencies (conducted and radiated)
The audio output power must be at least 20 dB below the rated output power when an unmodulated carrier at the receiver selected frequency and a level of 100 microvolts is applied and the equipment is subjected to the tests specified in RTCA DO-186 or later amendment.
5 Minimum performance requirements at low primary voltage
5.1 When all primary power input voltages are simultaneously reduced to 80% of normal rated for DC, and 90% of normal rated for ac supplies:
(a) a signal-plus-noise to noise ratio of 6 dB must be obtained with an input signal level not more than 6 dB greater than that mentioned in paragraph 4.1; and
(b) audio output capability must be not more than 3 dB below that mentioned in paragraph 4.2; and
(c) the maximum time for the equipment to change from 1 channel to any other must not exceed 10 seconds; and
(d) mechanical devices must perform their intended functions.
6 Minimum performance requirements under environmental test conditions
Note Environmental test procedures are mentioned in Civil Aviation Order 103.21.
6.1 Altitude test
When the equipment is subjected to this test:
(a) there must be no evidence of arcing, burning or other deleterious effect; and
(b) the requirements of paragraphs 4.1 (Sensitivity), 4.2 (Audio output) and 4.12 (Spurious responses) must be met.
6.2 Depressurisation test
6.2.1 When the equipment is subjected to this test, it must continue to function as intended. Some degradation of performance may be permitted.
6.2.2 There must be no evidence of any condition occurring as a result of this test which may cause complete failure of the equipment.
6.3 Short time operating high temperature test
When the equipment is subjected to this test:
(a) there must be no evidence of overheating of any component or exudation of grease or other compounds; and
(b) the equipment must continue to function as intended. Some degradation of performance, within the following limits, is permitted:
(i) sensitivity must not decrease more than 6 dB below that mentioned in paragraph 4.1; and
(ii) audio output capability must be not more than 3 dB below that mentioned in paragraph 4.2.
6.4 High temperature test
When the equipment is subjected to this test:
(a) there must be no evidence of overheating of any component or exudation of grease or other compounds; and
(b) the requirements of paragraphs 4.1 (Sensitivity), 4.2 (Audio output), 4.4 (Audio frequency response), 4.5 (Automatic gain control), 4.11 (Selectivity) and 4.19 (Operation of mechanical devices) must be met.
6.5 Temperature variation test
When the equipment is subjected to this test, the requirements of paragraphs 4.1 (Sensitivity), 4.2 (Audio output), 4.4 (Audio frequency response) and 4.5 (Automatic gain control) must be met.
6.6 Low temperature test
When the equipment is subjected to this test:
(a) sensitivity must not decrease more than 6 dB below that mentioned in paragraph 4. 1; and
(b) audio capability must be not more than 3 dB below that mentioned in paragraph 4.2; and
(c) the requirements of paragraphs 4.4 (Audio frequency response), 4.11 (Selectivity), 4.15 (Channel selection time) and 4.19 (Operation of mechanical devices) must be met.
6.7 Humidity test
6.7.1 After the equipment has been subjected to this test, and immediately following the 15 minute warm-up period, the audio output capability must be not more than 10 dB below that mentioned in paragraph 4.2.
6.7.2 Within 4 hours from the time primary power is applied, the requirements of paragraphs 4.1 (Sensitivity), 4.2 (Audio output), 4.4 (Audio frequency response), 4.5 (Automatic gain control), 4.11 (Selectivity) and 4.19 (Operation of mechanical devices) must be met.
6.8 Resonance search
When the equipment is subjected to the resonance search, there must be no evidence of excessive flexure of the chassis or mounting and components must not develop independent movement which would be likely to result in failure of the component or its attachment to the equipment.
6.9 Anti-vibration mounting attenuation test
When the equipment is subjected to this test:
(a) the mountings must not attain their limit of displacement in any direction; and
(b) magnification of vibration amplitude must be confined to frequencies below 20 Hz.
6.10 Vibration test
When the equipment is subjected to this test:
(a) there must be no evidence of detuning, upset of adjustments or other malfunction; and
(b) the requirements of paragraphs 4.1 (Sensitivity), 4.2 (Audio output), 4.3 (Distortion) and 4.4 (Audio frequency response) must be met.
6.11 Acceleration test
After the equipment has been subjected to this test there must be no evidence of it breaking free from its mountings.
Appendix 1
Test procedures
1 It is recognised that compliance with some of the minimum performance requirements mentioned in this Civil Aviation Order may be determined using alternative test procedures. However, paragraph 3.8 states that “accepted” test procedures are to be used and the Director may require a full description of the procedures actually used should there be any doubt as to the validity of the results of any test.
2 Procedures suitable for the conduct of most of the tests mentioned in this
Civil Aviation Order are contained in RTCA DO-186 or later amendment. In some instances, suitable procedures may be determined from the wording of the requirement.
3 For the convenience of manufacturers who do not have ready access to RTCA DO-186 or later amendment, or certain of the test equipment mentioned in it, the following information on acceptable test procedures may be useful.
3.1Cross modulation (paragraph 4.13 refers)
(a) Connect 2 signal generators via a suitable “T” pad to the receiver input. The pad should provide suitable termination and isolation for the signal generators and receiver. One signal generator will supply the “desired” signal, the other the “interfering” signal.
(b) When using the “T” pad, the RF signal levels specified are the “open circuit” levels at the output of the “T” pad with the receiver disconnected.
(c) With the “interfering” signal generator deactivated, set the “desired” signal generator, modulated 30% at 1 000 Hz, to the receiver frequency and levels mentioned in paragraph 4.13.
(d) Set the receiver gain control to give a convenient output and record this. Do not further adjust the gain control.
(e) Remove the modulation from the “desired” signal and set the “interfering” signal generator, modulated 30% at 1 000 Hz, to the level and frequencies mentioned in paragraph 4.13.
(f) Again, note the output of the receiver and compare with the output due to the desired signal when modulated.
3.2 Spurious emissions (paragraph 4.14 refers)
3.2.1 Emissions from antenna
(a) Connect a suitable tunable receiver — such as a field intensity receiver — to the antenna terminal of the receiver under test. Ensure that correct impedance matching is achieved. The receiver under test may be set to approximately 120 MHz.
(b) Tune the tunable receiver across the specified frequency range and note the presence and level of signal indications.
(c) A signal generator in place of the receiver under test may be used to determine the levels of noted signals and these converted to power by calculation.
3.2.2 Emissions from interwiring
(a) The test conditions should simulate a typical installation in an aircraft.
(b) Mount the equipment by its normal means, approximately centrally, on a copper, brass or aluminium groundplane measuring at least 0.76 metre or 30 inches wide and having an area of at least 1.1 square metre or 12 square feet.
(c) This test should preferably be conducted in a screened room with the groundplane connected to the room shielding by low reactance paths from at least both ends of the groundplane.
(d) Where the length of interconnecting cables is not specified by the manufacturer, these should be at least 1.52 metres or 5 feet long and arranged as in a typical installation. Cables should be raised about 50 mm or 2 inches above the groundplane to reduce shunt capacitance effects. Only those cables so specified by the manufacturer in wiring diagrams applicable to the equipment may be screened.
(e) Bonding straps across vibration isolators, etc should be fitted where these would be used in a normal installation. Bonding must not be used in any place where it would not normally be used in an installation.
(f) Tie in with each bundle of cables in the simulated installation an 18 or 20 gauge insulated cable, unterminated at both ends. Connect a suitable tunable receiver — such as a field intensity receiver — to this “pick-up” cable.
(g) Tune the tunable receiver across the specified frequency range and note the presence and level of signal indications. A signal generator may then be used to determine the levels of noted signals.
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