Product Focus: Expanding Scope of ARINC 625 Test Equipment 

By Andrew D. Parker | August 1, 2006
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The ARINC 625 commercial aviation standard for testing line replaceable units is being revised to accommodate the expanding role of electronics in new aircraft design. The resulting approach will be more inclusive and generic.

The pace of technological evolution constantly accelerates. Electronics systems are already pervasive in modern aircraft. In future aircraft designs such as the Airbus A380 and the Boeing 787, however, electronics also will impact components that are not traditionally considered avionics, such as the hydraulic, pneumatic and environmental control systems. In the "more electric" aircraft, for example, the hydraulic system will be connected to an actuator that is controlled by an electronic module, using fly-by-wire technology, instead of a mechanical link.

This evolution has brought about the need to restructure ARINC 625, "Quality Management Process for Test Procedure Generation," a standard that covers testing line replaceable units (LRUs) with manual and automatic test equipment (ATE). The Avionics Maintenance Conference (AMC) is in the midst of a revision known as ARINC 625-2.

AMC’s Test Program Set Working Group is reorganizing ARINC 625 according to industry feedback, restructuring the standard to improve clarity and adding a reference to ARINC 668, which is a separate standard for tool and test equipment equivalency. ARINC 625-2 seeks to define test specifications for next-generation aircraft programs, such as the A380 and B787, but also will continue to apply to current and legacy aircraft.

Published in the mid-1990s, ARINC 625 was originally defined only for ATE-testable LRUs. It covers the technical support and data packages (TSDPs) that avionics original equipment manufacturers (OEMs) should supply to third-party test program set (TPS) providers as the prerequisite for high-quality test solutions. ARINC groups take a fresh look at standards about every five years, and in 1999 the working group published an update known as 625-1.

For 625-2, the working group is seeking to make the document more generic and easier to work with, relating to all types of test programs. The implementation-specific data will be moved into appendices or attachments at the end of the document. The title also will change to reflect a wider scope: "Industry Guide for Component Test Development and Management."

"We tried to make ARINC 625 more general and applicable to any kind of test implementation, whether it’s ATE, or semiautomatic test, or dedicated test, or whatever you have," says Axel Mueller, chairman of the AMC working group and manager of processes and controlling for the Component Maintenance Services division of Lufthansa Technik.

Expanding the scope beyond ATE will allow the working group to provide a "dependable, complete test information tool" for operators who want to develop their own test solutions or rehost a test on a different piece of test equipment from that used by the OEM. This is typically referenced in the component maintenance manual (CMM), as well, Mueller says.

"By making the document more generic, we will avoid the relationship to avionics only," he continues, adding 625-2 will be more concise and readable. "Furthermore, by restricting the main part of the document to the essentials, we will facilitate the use of 625 for any application."

"The terms that we use in 625-1 are understood in the avionics shop, but we want to be able to have the people who are actually testing the hydraulics and the pneumatics and other equipment to be able to understand it," says Troy Batson, a member of the working group and senior field applications engineer with Aeroflex.

The emergence of more electronics on aircraft and the airlines’ interest in having more control of their assets will probably increase the number of ARINC 625 applications. "As new equipment is built and new capabilities are developed, there’s potential for growth of additional 625 specifications," says Gary Schwab, product support manager for Rockwell Collins. Those growth areas could even include motors or generators, he adds.


Another reason the AMC group is updating the document relates to ARINC 668, "Guidance for Tool and Test Equipment Equivalency." That standard covers the equivalency determination for tools and test equipment, including anything from a screwdriver to an ATE. Because it was published after 625-1, ARINC 668 contains parts that overlap with some of the material in 625-1. For instance, 625-1 includes references to a number of procedures and guidelines to determine equivalency between an independent test provider and OEM test specifications defined in the CMM. According to Mueller, ARINC 668 contains a much more detailed and clearer version of similar overlapping material in 625-1. Because of that duplication, the committee is adding a reference to 668 in 625-2.

Another problem with previous versions of ARINC 625 was that manufacturers would send incomplete information to the operator or third-party TPS provider. In 625-2, the working group will define the TSDPs to include test specifications and any additional information needed to implement a test. "Our goal is that if the OEMs comply [with] what we’ve defined in 625-2, we will ensure that the TPS provider will get high-quality and complete test data," Mueller says.

The methodologies used to evaluate avionics test equipment are changing rapidly with the advancement of technology, as well. In some cases these days, once a standard is adopted, it has already been surpassed by technological evolutions. "This is the exact reason why we want to keep the 625 standard as generic as possible," Mueller says, and confine the OEM-provided information to TSDPs.

An example of this concept is the ATLAS (Abbreviated Test Language for Avionics System) programming language. Originally, ARINC 625 referenced ATLAS test specifications, but as components became more complex, ATLAS ultimately fell short because it did not transfer all the relevant data required for testing.

"It made it difficult to take an ATLAS specification from one implementation on an ATE and transfer it over to another implementation on an ATE," says Batson. As a result, ARINC 625-1 was established to include commercial off-the-shelf (COTS) tools such as the C++ programming language, in addition to ATLAS. The revision sought to close the gap between ATLAS-provided data and the actual specifications needed by test engineers.

Now, the standard is not tied to ATLAS or any other programming language or methodology. With 625-2, Batson says, the group decided "not to specify what language to use from one system to the next." Any method, including ATLAS or the graphical test tools of today, will be supported by 625-2.

The working group also is looking at ways to minimize costs for the TPS provider. "You want to be able to take the OEM document, whether it’s a CMM or some kind of test specification that’s written for a test system like ATLAS, and very closely and easily relate it to your new test implementation," says Batson. If the AMC group defines methods that make it easy for the TPS provider to understand the OEM-supplied document, he continues, "then that reduces the cost of the equivalency verification, because it becomes more obvious how the implementations are equivalent."

The working group expects a final draft of ARINC 625-2 at its next meeting in September 2006 and hopes to see the standard adopted by the next AMC in April 2007.

Once ARINC 625-2 is published, the working group will take steps to ensure the update is referenced in the CMM portion of the Air Transport Association’s iSpec 2200, other related industry documents and OEM support agreements. According to Mueller, while ARINC 625-2 simply offers guidelines for testing, adding the standard into those documents ensures that the revision will be binding in future purchase agreements.

Software Configuration Management

With more aircraft systems shifting to electronic controls, software implementation issues are coming to the fore.

"The more electronic boxes you have, the more software controls you have. There’s almost no electronic box these days where you don’t have to load software to make it run," says Axel Mueller, chairman of the Avionics Maintenance Conference (AMC) working group, which is drafting a more inclusive and generic test standard known as ARINC 625-2.

"Software can present a lot of different challenges in how it gets tested on an aircraft," says Gary Schwab, product support manager for Rockwell Collins. He adds that applications using "onboard loading," where the actual box remains in the aircraft for software loading and updates, are increasing.

Some avionics units can be updated via onboard loading, but in cases where an avionics unit is removed from the aircraft, shop technicians must be able to reload the software into the unit.

Because of the increased use of software, the AMC group is seeking to add "requirements related to software loading in the shop," Mueller says.

Another issue the working group plans to discuss is configuration management, involving software loaded into avionics units. Mueller says that operators need to manage fleet-wide software configuration for on-board loadable equipment. And all data and procedures have to be consistent with software configuration management procedures on the aircraft workshop level. The working group plans to examine software loading, security and configuration management related to ARINC 625-2 at its next meeting in September.


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