When commercial airframe OEMs develop a multiple-aircraft family, parts commonality is among the major selling points. But over time, this advantage may erode with new variants and the movement of aircraft among different operators due to sales, leasing or mergers. This means that even where common fleet types are concerned, parts provisioning can be a planning challenge.
“Even if an airline operates the same fleet type, it has to maintain one common modification standard to fully interchange the parts within that fleet,” says Frank Martin, executive director and head of maintenance practice for the Seabury Group in London. “The operator has to decide the modification standard he wants to have in the overall fleet or within certain subfleets—where he can use an older modification standard—or write the parts off and purchase new ones.”
That, however, can present its own set of issues, especially in cases of long-running production cycles, according to John Avery, commercial director, AJW Aviation in the U.K. “There is a [commonality] attrition rate as the platform develops,” he says, specifically citing—as the best example—the Airbus A320, which is now in its fourth generation.
“Over those four generations, what Airbus did was to introduce more computing power to the A320, which decreased the number of black boxes used on later models,” Avery says. “That means that a black box used on a second-generation A320 will not necessarily be applicable to the third-generation equipment, which [is] still widely used. More complicated provisioning from one operator to the other has resulted.” Avery adds that the first-generation A320s, built from the mid-1980s to the early 1990s, are essentially gone.
But as parts themselves age, that also affects their interchangeability. “Some operators—and all leasing companies—do not want old components on younger aircraft,” says Avery. “A typical lease-return clause usually requires no component to be older than 110% of the age of the aircraft.”
Avery says that in most cases components can be economically modified to preserve commonality, and he does not consider that to be a major cost-driver, at least in cases where airlines are operating large fleets or similar types. “Where it can have a major impact is [on] a small operator with a diverse fleet,” he cautions. “They have the choice of spending even more money on the diversity or risking disruptions.”
Parts commonality need not be a significant issue as long as good configuration management exists, says Sean McGovern, managing director, BAE Systems Regional Aircraft in Prestwick, Scotland. Citing the company’s continued support of its out-of-production BAe 146 and Avro RJ regional jet families, he says that parts have been upgraded with retrofit in mind.
“At the same time, obsolescence management is clearly an important element—especially with legacy aircraft,” McGovern says. An example is the trend toward cockpit upgrades in which cathode-ray tubes are being replaced by liquid-crystal displays.
Johann Bordais, vice president, services and support at Embraer Commercial Aviation in Brazil, reports that improvements typically developed during an aircraft’s production life and applied on the assembly line are also recommended to the fleet already in operation. “If the airlines find it worthwhile to implement those developments in their operating aircraft, configuration, production and field operation continue with high commonality,” says Bordais.
According to Todd Young, vice president/general manager-customer services for Bombardier Commercial Aircraft, the OEM works with suppliers “to ensure that the latest mod status parts are interchangeable with the older components,” and that the older components are upgradable as part of the repair process, through the incorporation of service bulletins.
“We find that airlines may incorporate product evolution changes during heavy maintenance checks, thereby increasing the level of parts commonality within their fleet,” Young says. “As the product evolves, Bombardier strives to make parts retrofitable.”
Young says the OEM’s popular CRJ regional jet series has a 97% parts commonality level, while for the new CRJ 100/300 series it is 95%.
Fleet commonality is often seen as a benefit of some airline mergers. But even when similar fleet types are involved, common components may differ by configuration and modification status. Service bulletin work is a case in point.
“When two companies are brought together, they will likely have different maintenance planning policies. One airline’s technical department may give a component service bulletin a high priority, while another’s may decide that it is not worth compliance because it does not impact safety or reliability,” Avery points out.
Airline mergers also can mean inventory surplus. “This may happen when the pre-merger, individual airlines had adopted inventory self-ownership, whereby the harmonization of the stock planning strategies may lead to asset excess,” explains Bordais.
Among the advantages of parts commonality are economies of scale, but that may depend more on fleet size than a common aircraft type.
“For narrowbody aircraft, the fleet size where the real spare-parts scale effect is achieved is in the range of 40-50 aircraft of the same type operated out of a single hub,” says the Seabury Group’s Frank Martin. “A lot of airlines don’t achieve the full scale on their inventories and either operate suboptimally or seek pooling agreements through the major MRO providers or OEM programs.”
According to AJW Aviation’s John Avery, what complicates this is the fact that most components today are more reliable and only need to be changed once every few years or less. This, he says, means that forecasting has become more difficult and errors become more costly, because there is the risk of overstocking some parts that may not be required as often.
“Beyond wheels and brakes, and the next 50 most frequently used part numbers, the forecasting situation is very erratic,” he says. “Unless you have a very large fleet, it is almost impossible to forecast in the traditional sense. This is one of the main reasons why pooling solutions provide such good value.”
Along with significantly less capital risk, a parts pool saves the operator the cost of becoming involved with parts management at the “granular level”—the lowest level of detail, down to individual parts numbers, says Avery.
“When you get down to managing at the part-number level, you are essentially stepping off a cliff, because you have to forecast how many of each individual part number will be needed,” he notes. “That gets into a very difficult, very complex planning process.”
Given the high cost of components on such new-generation aircraft as the Airbus A380, A350 and Boeing 787, Seabury’s Martin says the industry trend is to shift parts management in the direction of comprehensive spare-part pooling programs offered by the major MROs and OEMs. “These suppliers define their pool standards on a large[r] scale and provide their service at a level specific to the airline’s need. They normally cover the provision of an on-site stock to support specific service levels, the replenishment, the maintenance and modification as well as the logistics and financing of the parts,” he says.
For some airlines, an OEM parts pool in combination with other vendors is a more viable option. That is the case with Hayden, Idaho-based Empire Airlines, which operates a fleet of 18 ATR 42/72 freighters in a dedicated feeder service for FedEx, as well three ATR 42s used in intra-Hawaii passenger service ‘Ohana by Hawaiian Airlines.
According to Wendy Martini, Empire’s purchasing manager, ‘Ohana participates in ATR’s Global Maintenance Agreement pooling program for all parts and components. For Empire Airlines itself, the carrier uses multiple suppliers within the FedEx preferred-vendor network in most cases. Configuration issues, she reports, have not been a problem.
“We identify the part’s specific configuration and order to that,” Martini explains. “If we have a component system that differs from model to model, we try not to stock all the possible configurations of that component at any one time, but order as needed. However, if it’s a unique configuration, we’ll stock in advance for that,” she says.
Martini credits FedEx with keeping components in an identical configuration on all the aircraft it assigns to its feeder partners, so there have been no bridging problems with any airplane transferred by FedEx into the Empire fleet. While it has not been a serious problem, there have been a few situations involving component backward compatibility. “Where we have seen that has been mostly with modified or upgraded components, which are not always compatible with an older platform,” she says.
In some cases, parts configuration can be identical across an aircraft family, but part numbers stand in the way of interchangeability. A case in point is Luxembourg-based Cargolux, which operates 13 Boeing 747-400Fs and the same number of 747-8Fs—for which it was the launch customer.
“The 747-400 and the 747-8F have many parts in common, but because the 747-8F was certified under its own set of part numbers, we cannot use the identical components used on the 747-400F,” explains Raymond Greff, the airline’s director, material management and maintenance and engineering contracts. “The problem is that the 747-8F part numbers are more expensive to purchase, and of course we have the cost of maintaining two separate supply chains,” he says.
Setting up a parts pool called GATS with Atlas Air—mainly focused on 747-8 components—has helped mitigate the investment costs of the newer-model spares. Greff notes that components for the 747-400F are still widely available new from Boeing and parts vendors, as well as the surplus market, as much of the global 747-400 fleet has been retired.