Big changes in aircraft maintenance tend to be driven by OEMs that design equipment and prescribe its care. But airlines and shops do perform daily maintenance, see equipment in action and constantly make small improvements to repairs. At present, many of these improvements involve exploiting aircraft data, using robots and 3-D part printing.
True data analytics is still in very early stages, limited partly by aircraft capabilities. Robots, UAVs and 3-D printing of replacement parts are also very new. But the search for new techniques for engine repairs is a constant.
Airline Reliability Index
Southwest Airlines has been profitable for 45 years by getting the basics right and continuously improving operations. It follows the same approach in its hangars.
The carrier has used Boeing’s Airplane Health Monitoring (AHM) management service since early 2014, notes fleet chief Ross MacArthur. Boeing collects data on 737s via about a dozen Aircraft Communications Addressing and Reporting System (ACARS) messages per flight, adds some analysis and posts results on a module of Myboeingfleet.com. Southwest MRO staff check the website frequently and ignore some “nuisance” alerts but pass real potential problems to maintenance planners to schedule repairs.
“In some cases, we see a lot of value, others we are looking into and still others it will be quite a while, if ever, before we exploit it,” MacArthur says. The primary gain has come in monitoring pneumatic bleeds. The carrier had been “almost blind” to such problems. Now temperature and pressure data on left and right ducts flag possible failures days or even weeks in advance.
As a result, pneumatics has dropped from first to sixth place as a reliability problem in just 12 months and should continue to recede. MacArthur also sees AHM value in monitoring performance of auxiliary power units during hot summer months and the condition of certain avionics like radio altimeters.
The carrier is in discussions with Boeing on adding sensors, for example, to air-conditioning outlets so it can spot problems before passengers complain. Eventually, it would like to have a continuous stream of quick-access recorder (QAR) flight data for analysis. It is probably too expensive to download the data by satellite during flight, but wireless QAR downloads at the gate are now feasible. They will come with the 737 MAX in 2017, and MacArthur hopes to retrofit the capability on 737NGs as well. “True predictive maintenance is where we want to go,” he says.
So far, AHM requires only one full-time Southwest staffer, and MacArthur is planning for the predictive future. Aircraft data-generating capabilities will account for that, he explains: “If the 787 is a 10 for generating and capturing data, the NG is a 4, and the MAX will be a 6 or 7.”
The savings from AHM are not mainly in reduced MRO spending but in avoiding the major revenue losses from delays, cancellations and disruptions.
Southwest sets its MRO priorities partly by using a new Airline Reliability Index (ARI), introduced in mid-2015. John Brutlag, director of aircraft standards, says the new ARI ensures concentration on the systems that are causing the greatest operational or safety concerns.
ARI scores every incident involving any of an aircraft’s up to 300 systems according to its seriousness. Least serious is a pilot or mechanic write-up, which gets a 1. Higher scores are given for delays, cancellations and returns to the gate. The highest penalty of 3.5 is given for an irregular operation such as an engine shutdown or diversion.
A high ARI score means a system receives an intense focus on its root causes. ARI helped bring pneumatics problems down, and Southwest is now working on some flight-cable challenges. Brutlag says the key is the scoring system, which ensures efforts focus on the most disruptive problems. Moreover, ARI will be a part of the airline’s drive to big data analytics. Eventually, Brutlag hopes the airline will be able to specify the maintenance effects of operational changes, such as altering turn-times at gates.
Here again, the main saving is in avoiding revenue losses from reliability problems that can be anticipated and fixed. Since introducing ARI, Southwest’s 737-700 and 737-800 mechanical dispatch and completion factors are up almost 0.4 percentage points, to 99.2%, on nearly 95,000 flights per month, and pilot-reported defects per 1,000 hr. are down more than 10%.
Robots and 3-D Printing
Some airlines are testing UAVs to inspect fuselages. Air New Zealand is testing a wall-climbing, camera-equipped robot—originally designed by Invert Robotics to inspect milk tanks—for the job. Andrew Hewitt, head of engineering contracts and leasing, says the robot should enhance safety and improve inspections. That is, it should avert any costs caused by injuries and ensure all damage is found and fixed the first time.
Manual inspection of a 777 requires elevating a technician 8 m (26.2 ft.), a risky height. Now someone on the ground can look at a screen showing the robot’s high-resolution camera image. All images are recorded and displayed with a graticule, a grid of lines that shows damage size. The airline considered UAVs, but a robot is better for non-destructive inspections. Hewitt says tests are underway, and the milk-tank robot may require modification.
And the carrier will soon 3-D print polymer parts for its business-class cabins. Five parts, including fold-down cocktail trays, ashtrays and latches, will be made this way. The aim is timely and cost-effective production of parts that are either obsolete or have long lead times for orders.
The airline uses selective laser sintering and fused deposition molding, common 3-D techniques used by aerospace OEMs, to print the parts. Nylon materials are used to meet aerospace standards, especially for retarding fire, and the parts must be tested for flammability.
Air New Zealand does not copy OEM parts but uses its Part 146 design organization approval to design and create 3-D parts with the right shape, size and color. For example, by exploiting 3-D potential, it can replace a solid part with a lighter hollow one.
Certification and production were near in early June, and ANZ is now looking at 30 more candidate parts that might be hard to obtain but easy to 3-D print. The airline is assessing whether it should own the 3-D machines or continue to work with a partner that prints the parts.
The carrier should save some money by 3-D printing replacement parts. Much more important savings could come from avoiding revenue losses from delays in obtaining needed parts.
Working with a university and 3-D software developers, Estonia-based Magnetic MRO has just 3-D printed prototypes of interior parts, explains COO Risto Maeots. The MRO gained experience by printing parts for tooling like painting blanks for wheels and brakes.
Magnetic’s first successes in interior parts have been armrest plastic covers and other plastic parts, including assemblies of several subparts such as passenger air nozzles. “The need is mainly for older aircraft, where lead time is long and prices high,” he says.
Magnetic used its own European Aviation Safety Agency (EASA) Part 21J organization to obtain approval of the printer, printing method and raw materials as well as its design for the parts, including performance, weight, hardness and flammability. In designing 3-D parts, the MRO will sometimes add strength if the OEM part frequently broke due to poor design.
Maeots says high-quality industrial 3-D printers cost too much to own for limited production. Printing costs 54% less than OEM pricing for parts that often take 2.5 months to arrive. Even so, it would take three years to recover its investment by printing 50 parts per month, and 3-D printers become obsolete fast. So Magnetic will partner with Stratasys, which owns a good selection of 3-D printers, and use ULTEM resins for fire resistance and mechanical and chemical properties.
One challenge is that 3-D scanners do not yet enable the simple scanning, replication and printing of parts. “It still requires time to draw a 3-D model of the part,” he notes. And regulatory approvals are much slower than printing speeds.
Magnetic is now working with a company that prints metal parts, including titanium and inconel, a family of nickel-chromium-based superalloys. It hopes to do larger-scale printing of both plastics and metals through a recent acquisition, MAC Interiors. And the MRO wants to 3-D print prototypes of structural repairs to ensure suitability before expensive production.
Magnetic should save money by 3-D printing replacement parts, and its airline customers by avoiding delays in delivery. For example, one plastic part cost $80 and took three months to procure on the aftermarket; 3-D printing and certification took three weeks and cost $55 for the same part. “I think similar gains exist overall comparing 3-D to conventional methods,” Maeots says.
On a rather different front, Magnetic is using HTC Vive high-definition 3-D glasses to give prospects a virtual tour of alternative cabin refurbishment schemes, including seat covers, carpets, curtains and lighting. It’s only a nifty sales tool, but it has “won some C checks,” Maeots observes.
Low Temp, Hot Savings
Critical to maintenance economy is any saving in engine MRO costs, which account for about 40% of total MRO spending. Fortunately, the best engine shops are developing better, less costly or less time-consuming techniques for repairing corrosion, wear or other damage to engine parts.
For example, StandardAero Component Services has just begun using cold spray technology, according to Tim Mathis, director of engineering. Instead of a gun that sprays hot molten metal, cold spray uses high velocity to form a bond on impact. This minimizes problems due to thermal gradients and reduces the need for masking surfaces, which costs the shop $100,000 per month.
“It is a lower-cost, longer-life repair than adhesives or hot spray,” Mathis observes. It now works on aluminum and steel parts for which identical powders have been developed. Titanium and nickel-alloy parts are also candidates as suitable powders become available.
General Electric is testing the technique, too, and Standard Aero is therefore on the cutting edge of this repair method. Mathis thinks cold spray will eventually bring huge savings industry-wide, as it can repair some corroded parts with complex surfaces, costing up to $200,000, and it can deal with corrosion on complex surfaces that must now be scrapped.
Standard Aero also will also use cold metal transfer, a welding alternative to gas tungsten arc welding, for simpler repairs. Mathis says this yields less distortion and degradation of the part under repair and thus expands the number of components that, like fan cases, must now be scrapped but could be repaired with the new technique. Cold metal transfer also reduces tooling costs.
The technique is being certified and tried out in production. Standard Aero is working closely with OEMs on its development.
Laser cladding is another lower-temperature, lower-force technique for smaller repairs. Its more controlled welding leads to less distortion and easier post-weld processing. Again, Mathis says, it should enable repair of parts not recoverable by conventional welding.
These three new techniques should produce savings in several ways: decreasing repair costs; avoiding the cost of purchasing now-repairable parts; and avoiding do-overs thanks to more long-lasting repairs. But Mathis says it is too early in development to quantify these benefits.
Beyond repairs, the shop is streamlining its administrative processes. Rick Stine, president of the Component Division, says Standard Aero is going paperless with its e-shop order system that will capture all data electronically. This step will enhance controls on inspections. “You will not be able to take the next step unless the last is closed,” Stine explains.
It will also support much better capacity planning based on data collected by e-shop and taken from historical systems. “We will know where the bottlenecks will be weeks before they happen,” Stine says. The results for Standard Aero should be greater efficiency and faster delivery, and for customers, better predictability that should in turn allow them to hold less inventory. The shop expects to have these systems in place by the end of this year’s third quarter.