What Is Audio Frequency?
This test is conducted to evaluate the immunity against audio frequency distortions imposed on power inputs within the scope of Chapter 18 (“Audio Frequency Conducted Susceptibility – Power Inputs”) of the RTCA DO-160 “Environmental Conditions and Test Procedures for Airborne Equipment” standard. DO-160 is the exact same text as EUROCAE ED-14 and is recognized by ISO as ISO 7137.
Purpose of Audio Frequency
The purpose is to certify that aviation equipment meets the requirements for assessing immunity to audio frequency distortions imposed on power inputs in flight and ground conditions and to complete equipment qualification.
Which Products Is Audio Frequency Applied To?
- Avionics units and displays
- In-flight electronic equipment
- Communication and navigation devices
- Cabin and cargo compartment equipment
- Sensors and actuators
In Which Sectors Is Audio Frequency Used?
Standards Related to Audio Frequency
- RTCA DO-160Environmental conditions and test methods in aviation equipment test
- EUROCAE ED-14
- ISO 7137
Audio Frequency Conditions
- Frequency range
- Standard defined audio track
- Seviye
- Defined by category
- Application
- With series coupling to power line
- Screening
- Frequency band is scanned step by step
Equipment for Audio Frequency
- Signal generator and power amplifier
- coupling transformer
- Oscilloscope
- Function monitoring
Sample Requirements for Audio Frequency
- Category must be defined
- Power line access must be provided
- Function monitoring must be set up
Duration of Audio Frequency
Typically half a working day.
Audio Frequency Procedure
- 1The coupling arrangement is established and the level is calibrated.
- 2The frequency band is scanned.
- 3Repeat for each power line.
- 4Function is monitored continuously.
Audio Frequency Acceptance Criteria
The acceptance criterion is that no functional impairment occurs.
Evaluation of Results
The frequency of the distortion provides input to the feed filtering design.
Audio Frequency Report
- Applicable standard, revision and Part 18
- Selected equipment category and justification
- Applied conditions and measurement results
- Function monitoring method and observations
- Environmental Qualification Form (DO-160 Environmental Qualification Form) entry
Accreditation
EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.
Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.
Scope and authorisationsRelated Regulations
- Aviation equipment qualification requirements
- EASA/FAA certification principles
Aerospace Testing — What Does This Testing Field Cover?
The section below describes the field that the Audio Frequency test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.
Aerospace testing shows that equipment keeps working in the flight environment and provides evidence for the airworthiness file. In this family the acceptable probability of failure is several orders of magnitude lower than in other sectors; this directly determines the scope of testing and the certification burden.
The most distinctive feature of the field is TRACEABILITY. Which melt an aircraft part came from, in which heat treatment furnace and with which cycle it was processed, which operator made the weld and which inspector approved it are all recorded. The test report is one link in this chain; if the chain is broken, the report carries no value on its own.
Environmental qualification runs through RTCA DO-160, with categories selected according to the equipment's MOUNTING LOCATION in the aircraft. A device mounted on the cockpit panel and one mounted inside the wing pass the same section under different categories. When reading a DO-160 report it is therefore essential to know which sections were applied at which categories.
On the software and complex hardware side the approach changes entirely: the evidence is not testing but PROCESS ASSURANCE. DO-178C for software and DO-254 for complex electronic hardware define how the development process is to be run and which evidence is to be produced. Every step, from requirement to code, from testing of the code to coverage analysis, must be traceable. Testing software does not make it certifiable; the process record does.
A separate body of work applies on the material and special process side. AWS D17.1 is used for welding, SAE AMS 2750 for pyrometry in heat treatment and NAS 410 for non-destructive testing personnel. For special processes (heat treatment, coating, welding, NDT, bonding) NADCAP accreditation is effectively mandatory in the supply chain; without NADCAP it is not possible to sell parts to many OEMs.
On the quality system side the AS/EN 9100 series is used: 9100 for manufacturers, 9110 for maintenance organisations and 9120 for distributors. Without these certificates it is practically impossible to enter the aerospace supply chain, and audits are markedly more detailed than in other sectors.
Counterfeit part risk is a subject peculiar to the field. Separate standards and verification methods (visual inspection, X-ray, decapsulation and internal structure examination, XRF) are used to detect counterfeit or reworked parts in the electronic component supply chain.
Space applications add further layers: outgassing in vacuum, radiation tolerance, long-duration thermal vacuum cycling and assessment of single event effects.
Method groups in this field
Environmental qualification
RTCA DO-160 sections: temperature and altitude, vibration, shock, humidity, sand and dust, fungus, salt fog, fluid susceptibility, icing, lightning.
Electromagnetic
The EMC sections of DO-160; MIL-STD-461 and MIL-STD-704 power characteristics on military platforms.
Software and hardware assurance
DO-178C software life cycle and DO-254 hardware design assurance evidence; requirement traceability and coverage analysis.
Materials and welding
Welding qualification under AWS D17.1, mechanical testing of materials, metallography and non-destructive examination.
Special process control
SAE AMS 2750 pyrometry, coating and heat treatment process verification, preparation for NADCAP audits.
Space environment
Thermal vacuum cycling, outgassing, radiation tolerance and acoustic/vibration qualification.
Commonly confused in this field
- There is no such document as a "DO-160 certificate"; DO-160 is a test specification and its output is a qualification report.
- The selection of sections and categories comes from the customer's equipment specification; the laboratory cannot make that selection on its own.
- DO-178C and DO-254 cannot be satisfied by testing; the evidence is the traceability of the development process.
- An AS9100 certificate is not a product approval; it is a quality system certificate and part approval runs separately.
- For special processes, work carried out without NADCAP is not accepted in the supply chain even when it is technically correct.
- MIL-STD-810 and DO-160 are often confused: one is a military and the other a civil aviation specification, and their profiles differ.
Which decisions these results support
- Airworthiness and TSO/ETSO files
- Entry into the aerospace supply chain and supplier approval
- Special process approval and NADCAP preparation
- Determining the impact of a design change on qualification
- Managing counterfeit part risk and component verification
Related Tests
Frequently Asked Questions About Audio Frequency
How is the equipment category determined?
The category is selected based on the equipment's mounting location on the aircraft (pressurized/non-pressurized, heated/unheated area) and aircraft type. Category selection directly determines the test conditions and is declared in the qualification form.
Is there any difference between DO-160 and ED-14?
No. RTCA DO-160 and EUROCAE ED-14 are exactly the same text; the two are considered equivalent.