Avionics Testing Systems | Aviation Maintenance Magazine

Testing for unexpected avionics problems helps planes safely operate as scheduled.

Avionics systems play a critical role in aircraft safety and performance. Avionic systems manufacturers and designers must be confident in the reliability, endurance and safety of aircraft and engine components’ subsystems and full systems. Avionics test equipment used during the manufacturing and maintenance of aircraft avionics systems helps planes operate as scheduled and at peak efficiency. Also, this equipment assists engineers and aircraft companies ensure full compliance with heavily controlled federal regulations, specifications and standards. Aircraft structures must go through many levels of testing before receiving airworthiness certification by the Federal Aviation Administration (FAA) or Department of Defense (DoD).

Essential Equipment

Some consider avionics repair and testing equipment to be the most essential equipment used in the production, troubleshooting, repair and maintenance of aircraft and their avionics systems and instruments. Primarily used for calibration, inspection, evaluation and testing of various aircraft devices, avionic testing systems aim to inspect and resolve electrical and mechanical issues, conduct performance checks, and repair the brakes and other components of the aircraft.

The quantity and diversity of equipment and systems requiring testing in avionic systems equates to an equally complex range of test equipment. Avionics test equipment can be divided into two categories: general test equipment and specific test equipment. General test equipment can be used to perform tests on avionics systems in general, such as diagnostics, fault detection, and performance measurements. Specific test equipment is more specific and is used to test specific components or systems of a particular type of aircraft.

Actual test system equipment covers items from signal generators and digital voltmeters to autopilot servo test stands for clutch torque evaluation. Vacuum and pressure instrument chambers, manual turn and tilt tables, single axis rate tables and tachometer testers are some other common aviation test equipment. Bench-type equipment is primarily used for repair and alignment of avionics equipment and normally is larger in size than the smaller portable equipment used to service the aircraft on the ramp for troubleshooting.

Standard tensile, compression, shear and fatigue coupon tests, using the material properties quantified in these tests, help determine component material composition, dimensions, and joining methods. Designs must then be verified by testing individual components, systems, and entire airframe structures. Component and airframe tests allow for interactions between parts of an aircraft, providing the most realistic test scenario possible without actually flying the aircraft. Like coupon tests, full-scale airframe tests are conducted in static and fatigue loadings and can be conducted on undamaged or damaged airframes.

SET uses standardized modules from their construction kit that includes measuring technology, signal conditioning, power control units, software and hardware, to quickly and efficiently implement customer requirements for functional testers and production testing. SET Image.

Common Types

While there are hundreds of different aviation test equipment apparatus, here are two of the most common.

Over the past two decades performance flight testing of full-scale aircraft has transferred some of the testing workload to simulation-based systems. In addition to simulating flight conditions with their 3-D capabilities, simulators can create a realistic environment for aircraft system testing. They can find errors in aircraft functions, systems, and components in real time.

A computer simulation-based environment is not only less expensive than flight testing full-scale aircraft in a real-world environment but all the aircraft’s systems can be modelled in the simulation. In addition to mathematical modelling, other technologies behind simulation testing include real-time computation, motion actuation, visual image-generation systems and projection systems. All the aircraft’s systems, such as avionics and sensors, can be directly built into the simulation just as they would be on the actual aircraft. Simulation tests allow the use of extra measurement equipment that might be too large or otherwise impractical to include on board a real aircraft. Throughout different phases of the design process, different engineering simulators with various levels of complexity are typically used.

Benchtop test systems also provide a realistic environment for testing aircraft systems. Compared to simulators they are more compact, more portable, lighter in weight, less power-hungry, and require fewer maintenance personnel. They are also less expensive than simulators and can be used to test a wider range of aircraft systems. Many benchtop test systems are configurable and scalable. They can solve typical functional test coverage challenges throughout an aerospace product’s life cycle — and many are upgradable as test requirements evolve.

A testament to the versatility of benchtop aviation test equipment, Severn Beach, Solihull, United Kingdom-based GKN Aerospace has patents approved covering a new benchtop ice adhesion test device which incorporates apparatus to simulate icing conditions and then determine ice adhesion in situ. This will enable swifter, less costly assessment of promising ice phobic coatings and other ice protection technologies. Efficient ice protection systems lower power consumption, improving aircraft efficiency and lowering emissions.

Nondestructive Testing

Two of the most important methods for aircraft testing include the nondestructive procedures eddy current testing (ECT) and ultrasonic testing (UT). Compared to other NDT methods, ECT and UT can detect more flaws in less time and without the hassle of extensive setup times. With ECT, NDT analysts can cover surface defects and near-surface defects with greater efficiency and speed. UT also probes the same anomalies on a volumetric level and with the same expediency.

There are tools and equipment available that enhance ECT and UT functionality. This includes instrumentation with specialized capabilities that foster flexible scans and additional customization schemes. These are instruments capable of phased array ultrasonic testing (PAUT) and eddy current array (ECA), the most effective NDT methods of all the currently available options for commercial aircraft inspections.

Conventional ultrasound is more advanced than most NDT techniques and phased array ultrasound is better still. Traditional UT has inflexible scanning positions and limited customization options, preventing analysts from finding flaws in awkward angles. With PAUT however, inspectors can customize the beam shapes, adjusting the focus depths and achieve several angles. PAUT addresses the inconsistent thickness patterns of aircraft components. It’s also malleable enough to conform to the shape and texture of any component being tested.

At right is the ARA-552 Radio Altimeter Analog Adapter, designed to facilitate flight line testing of aircraft autoland systems, ground proximity warning systems and installed altimeter systems. Together with the ARA-552 Hand Held Controller, this set provides capabilities for testing a wide range of analogue altimeters in a variety of aircraft. Atlantis Avionics image.

Eddy current array enhances conventional eddy current testing through the multi-coil features in a single probe. The additional coils allow NDT inspectors to scan a wider radius while detecting more defects in less time. ECA has a very good best signal-to-noise rate (SNR), which boosts the probability of detection (POD). ECA probes can also spot hard-to-find anomalies in the form of pitting, surface cracks and corrosion.

Shown at left, is the TestStation LX2, Teradyne’s largest pin count in-circuit test system. The company says it is configurable up to 15,360 pins utilizing UltraPin II 128HD pin cards for testing large, complex and heavily-integrated printed circuit board assemblies. Teradyne image.

An Engine and Ice

Testing a jet engine in a test cell is crucial to testing and verifying proper performance of an aircraft in a controlled and safe environment. These tests include measurements of engine performance, such as thrust, fuel consumption and emissions, as well as assessments of the engine’s mechanical and electrical systems.

William Norman, program manager,
Swanda Aerospace, Oklahoma City, Oklahoma
Swanda Aerospace image.

The jet engine test cell ice detection system has been developed at Tinker AFB in conjunction with the U.S. Air Force who holds the patent. Swanda Aerospace, in agreement with the U.S. Air Force, is the exclusive worldwide provider of this unique, real-time ice detection system through our subsidiary, Integrated Icing Solutions.

For years, jet engine testing during cold ambient temperatures has been limited due to the risk of ice forming and causing foreign object damage (FOD) to the engine with associated significant costs. Our Ice Detection System measures ice formation and accretion rates based on real-time airflow rates associated with the engine inlet. The System continuously monitors for the potentially hazardous icing conditions, reporting on any weather-related changes as they occur. This results in more time testing engines, minimizing test cell downtime and the resultant costs.

The use of Ice Detection System enables operators to accurately identify icing conditions and recover 75% or more of the time normally lost in a jet engine’s test cell due to potential icing shutdown events.

Other Testing

Other aerospace tests include:

• Dynamic testing. Vibration, shock and acoustic noise dynamic testing equipment are in this group. Most vibration tables and shakers are capable of delivering up to 70,000 force/pounds, acceleration forces up to 750g and pyro-shock capabilities.

• Stress analysis and failure assessment. Materials fracture mechanics, fatigue, finite element analysis, inspection and welding tests are in this group to provide failure analyses.

• Cloud testing. This is a centralized testing system where testing data can be uploaded for all interested parties to view and interpret in real-time. Engineers can obtain information from testing data from other similar aircraft. They can then use this data to correlate with their own inspection.

• Environmental simulation. Environmental simulation chambers can test everything from individual devices to complete systems. Combined environment testing including temperature, humidity, altitude and vibration, explosive atmospheres, sand and salt fog and more are in this group.

• Fuel testing. Overall efficiency and performance of all-important fuel tank and fuel system components can be tested in this group. Fuel icing and contamination of fuel testing, helium leak tests, flow analysis, functional/qualification testing are available.

Testing Standards

Many standard test methods have been created for testing certain aviation materials. These test methods are published and updated by standards organizations such as ASTM, ISO, CEN, NASM, and DIN. Some of the more common include:

• ISO 6892-1 & 2 Metal Tensile Testing
• ISO 527 – Tensile Test of Plastics Composites
• ASTM C1273 Tensile Ceramic Test Equipment
• ASTM C1424 Compression Ceramics Test Machine
• ASTM D638 Tensile Testing for Plastics
• ASTM D695 Compression Testing for Rigid Plastics
• ASTM D4762 Polymer Matrix Fiber Reinforced Composites Test Equipment
• ASTM E9 Compression Testing of Metallic Materials at Room Temperature
• ASTM E8 Tension Testing of Metallic Materials

Avionic testing equipment can involve testing and simulation using standards such as MIL-STD-1553 and ARINC-429 and embedded systems such as multi-protocol modules and interfaces.

RTCA DO-160

RTCA DO-160 (Environmental Conditions and Test Procedures for Airborne Equipment) covers standard procedures and environmental test criteria for testing airborne electronic equipment and mechanical systems with numerous regulatory requirements. It ensures airborne equipment meet the airworthiness requirements for fixed-wing and rotary-wing aircraft. The most current revision, RTCA DO-160G, specifies tests that are typically performed to meet the requirements of the Federal Aviation Administration (FAA) and other regulatory bodies for equipment installed on aircraft. It has become a common testing standard recognized throughout the aerospace industry.

RTCA DO-160 is used by all major aircraft manufacturers to ensure that electronic systems and components are safe and reliable in any environmental condition. It is applicable for any aircraft, from business jets and helicopters to full-scale airliners. It includes 23 sections of test methods covering all aspects of the aircraft environment from temperature, altitude, shock, and vibration to RF emissions, lightning effects, and flammability.

13 Considerations When Choosing Automated Test Equipment

• Cost effective. How much will it cost to acquire a test bench and each test program/cable set? As mentioned previously, test benches are often designed to measure only one or two devices. Try to identify a system that provides multiple test capabilities in order to reduce the number of ATEs purchased.

• Robust. Does it have diagnostic and self-test capabilities to provide confidence that it is going to perform a proper test (and is not easily damaged by connecting a defective UUT)?

• Easy to use. Good designs should inform the user about its operation to some extent without every page of documentation. Controls provided need to be intuitive. Some tests are far too complex for this, but documentation can be integrated into the flow of the system’s use.

• Durable/Reliable. Are the connections, cables, etc., of a type and quality that will survive repeated use?

• Expandability. Not only can it do what is required, but does it provide options as requirements change or expand change over time?

• High test coverage. Some test solutions only touch major functionality items, but ignore edge cases. This results in failures in the field that cannot be replicated in the maintenance shop.

• Compact. If you are limited in space, finding a solution that is powerful but minimizes floor space or test tablespace is ideal.

• Comprehensive. Do the tests cover everything in the UUT (power, signals, communication, etc.)?

• Industry standard. What happens if the vendor that provided the test solution goes out of business or no longer wants to support their product? Using as many industry standard items (e.g., COTS test equipment, PXI/AXIe modules) as possible helps prevent this problem.

• Excellent customer/technical support. Have you spent many hours researching and finding a product that seems perfect for your test needs and environment, only to find out that after you secure it, support is virtually non-existent?

• Warranty/service agreement. A term of warranty is not enough information. What is the time from leaving your shipping department to coming back? How long does it take to get someone to provide a solution to your problem? Is the support email, phone, forum, or on-site?

• Proven track record. Has the company provided this product or solution before? Do they understand your work or just write software? How “polished” is the solution? Ask for the provider’s expert. If the “expert” is not as advertised or not available, look elsewhere for your solution.

• Third party testimonials. Talk to those using the solution or similar services. Get feedback. Not all negative reviews should be grounds for looking elsewhere but look for the trends.

Information provided by Duotech Services Inc.,
Franklin, North Carolina