How EMA Supports FAA Certification
Each day more than 45,000 flights take off across the Unites States. Each and every one of those planes has achieved certification. Aircraft certification is how the Federal Aviation Administration (FAA) manages risk to keep passengers safe.
Certification confirms that all FAA requirements have been met. It’s not just airplanes that need certification, but also unmanned aircraft, piloted balloons, and airships. The FAA says its certification processes are well established and have consistently assured safe aircraft designs. As a part of certification, the agency will conduct the following:
- Review any proposed designs and the methods that will be used to show that the designs and the overall airplane comply with FAA standards.
- Conduct certain ground and flight tests to demonstrate that the airplane meets FAA standards.
- Evaluate the airplane to determine the required maintenance and operational suitability for introduction of the aircraft into service.
- Work with other civil aviation authorities on their approval of the aircraft, based primarily on work already completed by the FAA.
The FAA has laid out what certification standards have to be met and what tests need to be conducted, but there is no step-by-step explanation of what order to go in. Because of this, the process has proven to be expensive and can add years onto an already long task if not done correctly.
“Certification in general is really difficult due to all of the different moving pieces and how integrated platforms require collaboration across structures, systems, electronics, and everything in between,” EMA Principal Scientist II Justin McKennon said.
Designing for lightning is a major part of the certification process. Commercial airplanes get struck by lightning on average one or two times a year. Damage from a strike can potentially damage not only the aircraft itself but also flight instruments.
EMA can streamline the lightning certification process, even if a physical model does not exist yet. EMA consultants have more than 40 years of experience working on the certification of aircraft and complex platforms. By using state-of-the-art simulation and analysis tools, EMA is able to determine the best approach to lightning protection programs to save overall man-hours to keep projects on schedule.
EMA simulation offers:
- Support for designing test coupons and subsystem tests.
- Simulation support for fuel system elements.
- Simulation of entire wings for 25.981 certification support.
- Certification and authority validation test and simulation support.
- Test execution and reporting.
- Custom material property measurement to ground modeling.
- Certification support and designated engineering representative (DER) services.
Benefits of using an EMA simulation model include:
- It is directly traceable to official CAD drawings.
- The configuration can be controlled and become part of the certification documentation.
- Rapidly provides design trade-off analysis.
- Provides structural currents and voltages to guide direct effects testing.
- Can be modified to provide certification support for aircraft upgrades and derivatives, payload integration, and other future activities.
“At EMA, what we try to do is leverage our experience… our lessons learned from working in the industry over the years and combine that with state-of-the-art simulation tools as well as our own measurement capabilities to really answer those questions far cheaper and far faster,” McKennon said.
Aircraft must be tested for indirect effects of lightning, direct effects of lightning, and lightning fuel systems. Indirect effects include what happens to the electronic systems inside the aircraft when they are exposed to coupled lightning currents. Direct effects testing determines lightning attachment points and current distribution in all critical aircraft structures. EMA has decades of experience not only determining this information but making sure it fits in with the production schedule.
“One of the things that I’ve seen that really gets people into a jam with HIRF and lightning, especially with certification of systems, is not understanding what all needs to get tested, what levels it needs to get tested, and what you have to do early on in the program to understand the scope of the process for certification,” EMA Senior Test Engineer Brock Milford said.
Milford has a background in direct effects of lightning testing. He has played a role in aircraft testing and says manufacturers not understanding how much time it takes to do a system level test can be a real challenge.
“Any system type test that you’re doing from scratch is a six-month minimum to a year-plus long process of just planning,” he says. “If you’re not thinking about that, you don’t have that scheduled early on in your program, it’s going to hurt. That’s the easiest way to put it.”
Time is not the only challenge facing aircraft manufacturers, completing required testing can be like putting a puzzle together.
The FAA typically requires you to run a suite of tests to show compliance. The agency recognizes several SAE Aerospace Recommended Practices (ARP) documents as acceptable methods for showing compliance. Some of these include:
- SAE ARP5414B, Aircraft Lightning Zoning
- SAE ARP5416A, Aircraft Lightning Test Methods
- SAE ARP5577, Aircraft Lightning Direct Effects Certification
Another common standard is DO-160 for the environmental testing of avionics hardware and MIL-STD-461 to test equipment for electromagnetic compatibility.
There is more to certification than just meeting these standards and recognized practices.
“Some of those tests don’t apply and how you navigate through that can be really challenging and it drives a lot of cost and schedule into it trying to figure out what to do there,” McKennon said. “One of EMA’s greatest strengths is being very nimble and agile in these processes because we’ve done it so many times.”
Lightning testing in particular is a challenge because it is so destructive. McKennon says it takes a long time to get materials that will just be destroyed. These parts have to be dissembled, evaluated, and measured to see what happens to them during a lightning strike. He says many times manufacturers are stuck levying equipment requirements on vendors before manufacturers know how they are going to react. This creates a highly conservative environment which could be incompatible with industry standard equipment.
“The earlier you find these things out, the better you can levy requirements on vendors, the less conservatism you need to apply to your design margins,” McKennon said.
Simulating Lightning Strikes
These challenges are easily addressed by using simulation. EMA developed Ansys EMC Plus to accurately model lightning indirect effects, direct effects, and lightning fuel systems.
EMA is able to prepare a basic simulation of an aircraft using CAD drawings and in-person talks about the type and location of various systems. This improves upon the fidelity of the levels versus using generic levels from standards documentation. EMA also has the capability to create existing cable routes to estimate lightning transients.
Fig. 1. Transport category aircraft CEM model developed for lightning ATL simulations. Exterior surfaces are shaded to show interior cable routing.
“A well-constructed simulation model is something that will mature as the project itself matures,” McKennon said. “As you mature the platform you can put better material properties in, bonding requirements, bonding resistance measurements things like that as you make measurements on the platform and that really gives you a way to access the aircraft without needing one physically there.”
Using simulation early in the design process allows you to test out different materials and designs without wasting time or adding to the cost.
“If you move something, the effects are systemic,” McKennon said. “You don’t know all of the features that it’s going to impact elsewhere in the platform.”
Using EMC Plus, EMA can provide specific recommendations for design changes that will improve the lightning protections. These design recommendations may be supported by additional simulations or testing.
“We can help identify the eventual safety assessment and some of the classifications for systems, for equipment level testing,” Milford said.
Fig. 2. Model of a full-aircraft with a return conductor system for the simulation. The cockpit and empennage have been omitted as they are unnecessary in this wing simulation.
EMA lightning resources include:
- Indirect effects of lightning (IEL)
- Specify initial transient control levels (TCLs)
- Design guidance for IEL
- Design circuit protection
- Evaluate the performance of structures, interfaces, and cables
- Determine actual transient levels (ATLs) for the aircraft
- Validate analysis
- Conformed equipment and subsystem testing
- Corrective measures
- Direct effects of lightning (DEL)
- Zoning assigning
- Set current distribution in structures
- Evaluate the performance of structures to lightning arc attachment and conducted current
- Design guidance for DEL
- Component and representative coupon testing at high current/ high voltage
- Corrective measures
- Lightning fuel systems
- Regulatory and program planning/ reporting
- Characterization of the electromagnetic performance of individual structures and systems
- Establishment of failure modes
- Determination of the EM environment during all scenarios
- Coupon testing
You can read more about each of these bullet points by clicking on this link-ema3d.com/lightning/lightning-introduction.
Fig. 3. EMA helped Douglas Aerospace save $1.6 million on the MD-90 indirect effects certification.
EMA has been a major contributor to commercial aircraft certification. EMA was the first to use computational electromagnetics for civilian certification of a complex transport aircraft on the MD-90. In this case, simulation was used to determine the inducted lightning transients at avionics box cable interfaces. The simulation approach was validated using existing experimental data obtained for certification of the MD-80 program. This validation was accepted by the FAA, eliminating the need for full-scale testing.
This process helped Douglas Aerospace save $1.6 million on the MD-90 indirect effects certification. Since that time, aircraft manufacturers increasingly rely on EMA and our simulation tools to support their lightning and HIRF certification efforts.
To learn more about the MD-90 projects and other work, click here.
Completing Lightning Testing
EMA provides test services for solutions to lightning design, analysis, testing, and certification. Our lightning testing services include:
- Indirect effects aircraft testing at your facility
- 981 fuel ignition testing
- 981 tank current/ voltage measurements
- DO-160 Section 22 equipment testing
Taking a look at general lightning testing, to start, each piece of the aircraft is categorized into a level. These levels will be used in determining whether each piece, especially the electronic devices, will survive a lightning strike. This is done by comparing the pieces to existing tests of equipment or estimating the likely susceptibility of each interface.
Once that is done, the aircraft is broken into three zones and a high voltage test will be applied to each piece of external equipment. This includes antennas, lights, and the radome. Zones are based on the likelihood for lightning attachment, lightning sweep, or lightning hang-on. This damage tolerance test tells us where that piece of equipment will be struck by lightning.
Fig. 4. An example of zoning of a wingtip. A full 3D CAD zoning can be delivered.
Next is a high current physical damage test. This is done by striking a piece of equipment with high voltage to determine what damage will occur if that piece of equipment does in fact gets struck by lightning.
Testing then moves to the avionics system of the aircraft. A pin injection test is conducted on each circuit, one at a time, to show damage tolerance.
From this point, a function point test comes next. This involves a system of an aircraft, such as an engine control system. Either a single stroke, multiple stroke, or multiple burst test is applied to a running system to find out if there is any type of upset based on the aircraft being struck by lightning.
“Now, the thing with functional upset testing, it is lightning testing done to what is considered a worst-case lightning strike,” EMA Principal Scientist I John DiNicola said.
This worst-case strike has a six dB margin on it. Since this is an upset test, it can damage a unit.
“You’re testing it to twice what you expect it to get and it’s very hard on the equipment, but at the end of the day, I mean, I know me, I fly all around the country, I don’t want to be on an aircraft struck by lightning and have an issue occur,” DiNicola said.
Along with lightning testing, EMA is also able to perform the following HIRF tests:
- HIRF aircraft transfer function testing at your facilities
- DO-160 Section 20 equipment testing
- PED testing
Fig. 5. During physical testing, electrical discharges are created in a structure enveloping the aircraft. Induced current passing through a critical component’s harness is measured to evaluate the effects of lightning strikes. Image courtesy of Embraer.
EMA is able to take the complicated certification process and create an easy-to-follow plan for manufacturers. We help you avoid having to make last-minute changes, meaning you’re less likely to face delays and unnecessary spending.
“The two biggest concerns on an aircraft are typically weight and corrosion and pretty much anything we recommend for HIRF and lightning adds weight and adds corrosion risk,” Milford said. “Some of the stuff that EMA can do for you is help think about these problems early on in the program, come up with some designs that can help pass HIRF and lightning certification. Those can get incorporated early.”
It is EMA’s experience that makes us stand out from the crowd as we are uniquely suited to handle EM environmental effects aspects of certification.
“We’ve got people that have been doing consulting and simulation for many, many years,” DiNicola said. “On top of that, we also have many people that have actually done the lightning testing, actually performed the lightning testing… EMA would definitely be one of the top choices if I were manufacturing an aircraft.”
Along with experienced engineers and scientists, EMA also has an FAA DER on staff. McKennon is a DER with full authority in HIRF, lightning, and related EMI/EMC areas.
“We know the process better than just about anybody,” he said. “When you combine the breath of programs that we work on through consulting, through aircraft level testing, with our equipment, and the certification experience, it’s really a unique blend that gives us sort of a best-in-class capability to help navigate these challenges.”