As airlines transition to a new generation of software-driven aircraft while continuing to fly older models with outdated electronics, industry concern is rising that avionics issues are a growing source of AOG (aircraft on ground) situations.

“Avionics are among the top five contributors to AOG,” says Kirk Thornburg, VP-technical services for Southwest Airlines. “Today's avionics do a lot of monitoring to assure that the redundancy in the circuits is working. If a fault is detected in any of the channels, you're advised to run a check before the airplane is dispatched.”

Chris Uphoff, avionics manager for Air Wisconsin, reports that about 50% of the carrier's AOG situations are related to aviation electronics. “This includes anything with mechanical movement, such as a weather radar, because of the moving parts.”

Copenhagen-based charter carrier Jet Time reports avionics contribute to about 30% of AOGs, says Karsten Schack, engineering project manager. “Of that, most have to do with the inertial reference system, VHF communications and the public address system,” he adds.

Based on the experience of TAP Maintenance & Engineering in Brazil, avionics most associated with AOG situations are the indicating systems, navigation, communication, electrical power and autoflight—in that order. “Hardware and software modifications have increased reliability, but that has led to increased system and component complexity, requiring even more trained technicians and expensive test equipment,” says Joil Pasqual, components general manager.

To appreciate airline worries, it is necessary to have some understanding of the concept of avionics.

“We define 'avionics' as anything with a wire on it—and that makes up a significant amount of aircraft content,” explains Mitch Klink, the steering group chairman of ARINC's annual Avionics Maintenance Conference (AMC). “While it is true that avionics [problems] can certainly create AOG situations with dispatch rates routinely in the mid-to-high 90% range, this is fairly rare.”

In the airlines' view, prevention of avionics-related AOG is ultimately a matter of the supply chain dynamics involving system original equipment manufacturers (OEMs), independent suppliers and MROs; as well as pooling arrangements among carriers. While airlines and suppliers contacted for this story are generally satisfied with their support arrangements, the pain points are many, and a one-size-fits-all solution does not exist.

Among the issues of greatest concern is a perceived lack of technical data sharing between avionics OEM repair facilities and their customers.

Technical Data

“This is a very challenging problem that is being debated by the industry today,” says Southwest's Thornburg. “By not sharing the data with the airline or independent MRO shop, it means that the operator must have the component repaired only by the OEM—or OEM-authorized service facility—and pay the price they ask since there are no other choices.”

Sarah MacLeod, executive director of the Aeronautical Repair Station Association, agrees, citing what she calls “a lack of clarity concerning the requirements for the design approval holder's responsibility” to provide information concerning basic maintenance.

“Federal regulations specifically state that repair instructions must be provided to the [aircraft] operator in order for that operator to assure continued airworthiness,” MacLeod says. “That would seem to imply that the operator will get all of the instructions and materials needed to maintain the airplane. But the issue that has evolved is, to what depth does the manufacturer have to go in order to provide those instructions? The FAA has never really answered that question.”

MacLeod adds that an airline is more likely to receive an on-wing troubleshooting manual that will only help to identify a problem. “It will normally advise that the unit be sent back to the manufacturer or supplier for repair.”

In the past several years, detailed repair information has been removed from the component maintenance manuals due the complexity of repairs—especially for new avionics and other electronic components, says Pasqual. Several CMMs have limited information, and troubleshooting has been limited to Level 2, he says.

“In some cases, even former Level 3 CMMs have been turned into Level 2 by removing specific schematic diagrams and information that once allowed a clear troubleshooting and repair process,” Pasqual reports. “This situation is leading many MROs to decrease the level of intervention they are able to perform on several avionics components.”

Complicating matters, avionics OEMs often carry out repairs based on their own internal documentation, says Michael Pierce, manager of component engineering at American Airlines' Tulsa, Okla., maintenance base. This can result in quality system and/or configuration control issues for some airlines, he adds.

“While airline engineering may be able to authorize repairs, alternative repairs and alternate materials in a component maintenance manual (CMM), the author of the CMM is the OEM, who is the only one who can provide an official revision release,” Pierce notes. “Sometimes, the OEM changes its maintenance practices by revising internal drawings and technical data but delays the revision of—or never revises—its CMM to reflect these changes.”

As a result, says Pierce, both airlines and MROs are often unaware of changes the OEM has made. “Given that the CMM is the FAA-recognized maintenance manual for a specific component, it should always provide the latest maintenance practices, materials, tooling, equipment and parts.”

Along this line, Pierce reports that in a case cited at the 2011 AMC, an OEM decided to modify a component, but never issued a service bulletin or otherwise reflected the modification in the CMM.

“The CFRs [Code of Federal Regulations] specifically state that all maintenance must be accomplished per the operator's maintenance manual,” he says. “When an OEM omits changes from the CMM and does the [repair] work per their internal documentation, they are no longer complying with that requirement.”

Configuration Conundrum

Air Wisconsin's Uphoff reports that the carrier has worked with avionics repair vendors to enforce compliance with its own maintenance manuals, repair specifications and specific work scope.

“If the vendor does have a different repair process than the one authorized by Air Wisconsin, we must review and approve it,” Uphoff explains. “That has helped to enhance reliability of the avionics and prevent AOG situations, especially on the basis of parts availability.”

Scott Gunnufson, VP, general manager for service solutions at Rockwell Collins, points out that some airlines have made a special modification to a particular component based on their individual needs. “In this case, we work with the airlines and keep a special set of instructions for repair on file, as required by the airline.”

Still, Southwest's Thornburg also confirms that third-party repairs to avionics are not always compatible with an airline's maintenance manual—especially in cases of exchange units. “The avionics databases are normally specific to the operational characteristics of an individual air carrier because each operator has unique climb profiles, fuel management techniques and engine thrust configurations” he says. “When a supplier of a common flight control computer repairs the same component for different airlines, they depend on the operator to provide these custom database inputs when the computer is returned from repair.”

Thornburg adds that if an avionics unit is returned to the airline with a generic software database setting instead of the carrier's custom settings, the operator must—upon receipt and installation—run check procedures to catch the incorrect settings in the database.

“If the software is not specific to the airline's requirements, there are two scenarios that occur. First, the airline's installation procedure requires the mechanic to verify the software level prior to releasing the aircraft. The second is that the aircraft will not accept the incorrect software level and fail the check-out procedure.”

Software configuration control problems, Thornburg suggests, could be mitigated using data transmission capabilities to and from the aircraft. “I think it's entirely feasible to have software integrity checks whereby the revision level of software for each piece of avionics equipment is frequently compared with a master file within the carrier's maintenance information system. Should anything not match, you have an immediate notification that there's a software discrepancy to be addressed.”

Obsolescence and AOG

While software updates are critical to high dispatch reliability numbers, the onrush of technology is leading to parts obsolescence issues, which can affect AOG rates. Thornburg confirms that avionics are, in fact, more prone to obsolescence.

“Airlines generally change more avionics/electronics parts to clear an MEL [minimum equipment list] due to the ability to quickly troubleshoot and determine if the avionics/electrical problem part fixes the problem. Also, longer lead-time planning for subassembly level parts is required in avionics/electrical components because the technology changes more frequently. As electrical/avionics components age, the older technology parts associated with these components are less in demand than subcomponents of pneumatic/hydraulic/mechanical type devices.”

American Airlines' Pierce reports that obsolescence is more of a piece part problem than a higher component assembly issue. “Occasionally, we find out about an obsolete part through advance notice from the OEM, or we discover it when trying to purchase a part. But, so far, alternate parts have been provided by the OEM or have been identified by our engineering staff to resolve obsolescence issues.”

AMC Chairman Klink explains that obsolescence issues involve mostly those parts that are installed on circuit cards encased inside avionics line replaceable units (LRUs).

“The problem is that when application-specific piece parts are certified for an LRU, their demand—several years later—is so low that it's difficult for the original manufacturer of those parts to retain the product line capability,” he says. “Keep in mind that commercial avionics represent less than 2% of the overall consumer electronics supply market. Most [of these] manufacturers are busy building piece parts for Xboxes and cell phones.”

Klink also points out that since avionics retrofits and upgrades are very expensive and difficult to justify in terms of their return on investment (ROI), airlines often maintain their existing components, which can present challenges for mature fleet types, some more than 20 years old. “Thankfully, the different product support agreements in place with component OEMs make provisions for obsolescence parts support. The OEMs are obligated to support aging components with obsolescence solutions as long as there are five aircraft of that fleet type still flying,” says Klink.

Parts obsolescence symptoms, says Southwest's Thornburg, normally manifest in the form of increased delays attributable to specific pieces of equipment. Another red flag pops up when the MEL allows the operator to fly with an item for an extended period.

“When this happens, we will investigate and contact the OEMs to find out why,” notes Thornburg. “Then, we will work with them to develop a recovery plan in order to be sure that the supply can be rebuilt to ensure that it meets our fleet requirements.”

Accomplishing that can take about six to eight weeks—on the low end. “I would call that a typical situation, in which more parts are built and made available to the supply line. If a more complex technical solution is required—say for a part that is no longer manufactured—it could take four to five months because a new workable component must be found, tested and certified,” says Thornburg.

To determine which solution provides the best ROI, the carrier will conduct a cost-benefit analysis. “We will then try to pay the best price for what meets the original part's specifications,” he explains.

Ingi Johannesson, manager of engineering for Luxemburg-based Cargolux, reports that repair agreements usually do not address the substitution of a totally new type of part for one deemed obsolete by the OEM. He points to a recent example in which the cathode ray tubes used on the airline's Boeing 747-400F and -400BCF cockpit display units are being replaced with LCD displays. “Fortunately, we've been able to find a vendor that continues to repair the cathode ray tubes, so that we won't have to replace them,” he says.

Jet Time”s Schack says he is not concerned about a parts obsolescence problem for his 737-300 fleet, given the current market, supplier agreements and his airline's long-term planning.

“We have sufficient inventory of components going forward and do not see an avionics availability issue for the 737-300 for at least the next 10 years. By then, we will have transitioned completely to the 737NG,” he says. “If a failure with a component that is not part of our consignment stock does occur, we have an agreement with our supplier that the component is to be delivered to us within 12 hours. If this cannot be done, we are free to contact another source. I urge any airline that depends on an outside supplier to furnish and repair components to make sure that AOG is specifically addressed in all contracts with that supplier,” says Schack.

Armin Jabs, president and COO of avionics OEM International Communications Group (ICG), reports that it is very typical to see relevant AOG clauses within new contracts. “Often this addresses both equipment availability and access to product support experts when needed. However, in larger fleets, where maintenance facilities may be across the globe, we are also seeing a tendency for operators to plan for sparing in strategic locations which helps all concerned,” he says.

Weigh The Options

While total failure of an avionics LRU is rare, there are programs airlines can use to mitigate avionics-related AOGs. As Klink of the AMC Steering Committee explains, one is an LRU quarantine, which provides for no-fault found components to be retained in serviceable stock instead of being sent through the repair cycle, making more spares available and saving some repair costs.

“Another recommended practice is LRU spares pooling, in which airlines share each other's LRU assets,” he says. “This reduces inventory costs because the airlines borrow each other's components, when needed, such as [for an impending] an AOG.”

One such shared assets agreement that includes avionics is the International Airlines Technical Pool (IATP)—website: The pool comprises 107 member airlines that meet twice yearly to develop agreements to provide specific parts—at indicated locations [see O&M, April, p. 63]. Ted Moos, Carloux director of maintenance and production, reports that the carrier is an IATP member and says, “The member airlines share the cost of the components, and in the event of an AOG, the required part must be available immediately to get the aircraft home. Once this is done, it is removed from the aircraft and returned to the pool member who supplied it.”

At times, an AOG can be caused by the malfunction of components with recurrent reliability issues. Marshall Barrand, director-aviation services for Flybe in the U.K., says that this issue is being addressed through managed and structured unit replacement programs by both the aircraft manufacturer and avionics OEM via component exchange programs, software upgrades or service bulletins.

“Some manufacturers,” explains Barrand, do this by providing seed units to kickstart this process, and some through attrition as units filter back through the shop. “To a certain extent, suppliers still expect airlines to purchase inventory in accordance with recommended spares purchasing lists provided. However, more often than not, this is not commercially necessary. More OEMs now offer alternatives to this by way of support agreements,” he says.

In some cases, the avionics OEM may work closely with the airframer to set up a replacement program by service bulletin/modification activity. “This is often driven by the airline/end user and the aircraft manufacturer—in the first instance. But, as always, liability for the costs can take as long to resolve as the actual fix itself,” says Barrand.

Avionics reliability and availability also may be enhanced as more airlines select third-party ownership and management of spares—a growing trend in the past three to four years, says Rockwell Collins' Scott Gunnufson. The game changer in this respect, he states, is the Boeing 787.

“More than any other aircraft, the 787 (which has a Rockwell Collins flight displays) has spawned a significant shift in industry thinking with respect to spares management and availability," Gunnufson says. More 787 customers are asking us if we are positioned globally to take care of their needs and if LRUs are located in enough places so that their aircraft can be dispatched, he says. “To ensure this, we are spending a lot of time today in global asset management and investment, using an installed database that tracks every one of our LRUs by flight hours and aircraft tail number. This not only puts us in a very good position to place components globally and to track failure trends, which further assists positioning. That will drive availability up and costs down.”

Adrian Paull, Honeywell Aerospace's VP-customer and product support, also sees trends toward third-party avionics ownership, management, repair and logistics, but notes some changes.

“For the past decade, we've offered our Integrated Support Solutions program, which started out being popular with startup, low-cost carriers acquiring brand new fleets,” Paull explains. “However, the subscriber base has begun to shift more to the major international flag carriers, but only in terms of a few individual part numbers that are extremely reliable on certain aircraft types. Because of their reliability, it's not cost-effective for the users to invest in test equipment. The fact is, many of our customers are staying with more traditional management models.”

Paull also cites another interesting trend. “When we sit on our customer advisory boards, we keep hearing the term 'imminent operational requirement' (IOR), which describes a situation that is less than an AOG, but will become an AOG if nothing is done about it. This allows us to sort out the urgent need from a critically urgent need,” he explains. “Your focus on AOG today is to plan ahead for proper resolution using the IOR concept to prevent AOGs. It's a matter of prioritizing what the potential is for AOG across the various components. More customers are raising this issue."