Product Focus: Test Equipment For the ‘More Electric’ Aircraft

By David Jensen | September 1, 2005
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The trend toward "more electric" aircraft, with mechanical and hydraulic components’ incorporating more and more electronics, has impacted and will continue to significantly affect aircraft manufacturing, operation and maintenance. It has affected component testing, too.

The trend already has spurred the Avionics Maintenance Conference (AMC) to take a fresh look at the ARINC 625 standard for testing line replaceable units (LRUs) with manual and automatic test equipment (ATE). Titled "Quality Management Process for Test Procedure Generation," the standard has seen limited application to date, according to Roger Goldberg, executive secretary for the ARINC-sponsored AMC. "The applications have thus far been limited to [test programs for] individual line replaceable units and not an entire airplane," he says.

Thou Shalt Comply

But that appears to be changing. Pressured by their customers, Boeing and Airbus "are saying that to be an electronic component supplier for their new designs [the B787 and A380, respectively], thou shalt comply with 625," says Goldberg. The airframe manufacturers’ airline customers seek greater test capability.

This situation, plus the emergence of what many call the more electric aircraft, is bound to cause applications of ARINC 625 to mushroom. The AMC’s Test Program Set Quality Working Group, therefore, decided that ARINC 625 clearly needed revision to broaden its scope.

At a meeting held in mid-July at ARINC’s headquarters in Annapolis, Md., the working group decided to launch the development of a revised standard, designated ARINC 625-2. This will make ARINC 625 more generic to accommodate components not traditionally thought of as avionics (e.g., hydraulics, pneumatics, etc.). Some might even say it applies to any wire with a component attached.

Key to Testing

ARINC 625-2 also would have a new title to denote its broader scope: "Industry Guide for Component Test Development and Management." The AMC working group considered the word "component" to be an inclusive term. Other revisions to the standard also were proposed.

Though it is not the only ARINC standard applicable to component testing, ARINC 625, originally developed in the mid-1990s, is key. It covers the technical support and data packages (TSDPs) that the avionics original equipment manufacturer (OEM) must supply to a third-party test program set (TPS) developer.

Specializing in test procedure development, third-party organizations such as EADS Test and Services and Aeroflex-JcAIR Test Systems are employed because they can customize test procedures to suit an airline’s special needs–say, develop a TPS for a designated grouping of components. Also, because some test programs were developed 20 years ago or more, the third-party organizations can, for example, "transport the test program to another [ATE] platform," says Goldberg.

With their own automated test solutions the airlines can check out components just as they were tested by the OEM, but without having to use the OEM’s test equipment and/or program. ARINC 625 defines the TSDPs in terms of the minimum data necessary for a component’s return to service and to support the level of testing defined in the component maintenance manual (CMM).

Initially, avionics OEMs delivered a test program using ATLAS (Abbreviated Test Language for Avionics Systems) programming language. But as components became more complicated and software-based, ATLAS proved to be inadequate for transferring all relevant data. "It provides only a piece of the data required," says Troy Batson, senior applications engineer with Aeroflex-JcAIR.

"The language is weak when it comes to implementing arrays and other aspects, especially when compared to today’s software," adds Bill Collier, manager of ground support engineering for Hamilton Sunstrand, an electronics component supplier. "ATLAS couldn’t describe all the procedures needed to produce the test program." Also, finding software engineers conversant in this outmoded programming language has become difficult.

Therefore, in the late 1990s, ARINC 625 was first revised to include a supplement that accommodates commercial off-the-shelf (COTS) tools, such as LabWindows, instead of ATLAS. "Now we convert the OEM’s [computer] code to the code we use," says Batson. The revision, designated ARINC 625-1, does not define the computer language that should be used for TPS development; that’s up to the third-party developer. Rather, it "defines the types of data required to develop the test," says Batson.

On to 625-2

The Test Program Set Quality Working Group recently investigated the need for 625-2 as part of the normal AMC procedures. (All ARINC standards are re-evaluated every five years or so.) But with the growing demands for more data to develop test programs, the working group quickly realized that a second revision is essential.

Interestingly, though the working group plans to make ARINC 625-2 broader in scope, it also plans to make the document, now 98 pages, shorter. Axel Mueller, the working group’s chairman and an official with Lufthansa Technik, proposed a "major restructuring" of the standard to make "it short and to the point." The standard’s appendixes, which largely provided background information and case studies, probably will be eliminated. "We also no longer need much of the background information about ATLAS," says Batson.

Another proposal is to have the updated standard reference ARINC 668, "Guidance for Tools and Test Equipment Equivalency," which was created in response to the January 2000 crash of an Alaska Air MD-83. ARINC 668 was developed to assure that an airline’s test program for a component is equivalent, but not necessarily identical to an OEM’s test program for the same component.

Completed Next Year

"There’s some confusion between 625 and 668," says Goldberg. He contends that the two standards will remain separate. "But we hope to establish wording so that TPS developers will produce TSDPs according to ARINC 625 and demonstrate equivalence using ARINC 668 to verify to the regulatory agencies that the test is equivalent."

Work on ARINC 625-2 has just begun. The Test Program Set Quality Working Group has a goal to complete the updated standard by mid-2006. However, the pressure to modify 625-2 will no doubt grow as airlines seek the ability to test more and more components.

A ‘Hot Topic’

The ARINC 625 standard offers little, if any guidance that would resolve a conflict concerning the quantity of data in the technical support and data packages (TSDPs) to produce test program sets (TPS). The conflict exists between the airlines, which want all the data they can attain in order to produce various test solutions, and the original equipment manufacturers (OEMs) of avionics, which want to withhold intellectual property that they consider competition-sensitive.

"Intellectual property and how we protect ourselves while satisfying the airlines’ needs is a hot topic," says Bill Collier, Hamilton Sunstrand’s manager of ground support engineering. The revision of ARINC 625 "gets us all talking about this topic, but it doesn’t resolve it."

"625 states what the airlines want, but it doesn’t help the OEMs determine what to provide while protecting their intellectual property," he adds.

Perhaps the conflict can best be put in perspective by bringing to bear the three levels of component testing. These levels, which are discussed in another standard, ARINC 663, are:

Level 1–for the test and repair of an LRU,

Level 2–for the test and repair of SRUs (boards within the LRU), and

Level 3–for the test and repair of components on a board.

"The airlines would like data down to the component level [level 3]," says Collier, "while the OEMs believe data at the board level [level 2] is sufficient."