Maintenance innovations make life easier for mechanics and operators

Aviation International News » October 2002
May 6, 2008, 11:05 AM

Aircraft maintenance does not exactly move forward technologically at the speed of light. Instead, it appears the industry is in a constant state of making things incrementally better. A small innovation here, some modification to an existing procedure there, a reemphasis on the importance of service, and the result is that operators get better, faster, more cost-effective maintenance. Take a traditionally difficult area of maintenance–aircraft painting.

Anyone, who has ever had the task of painting anything on an aircraft or, heaven forbid, the entire airframe, knows what a problem it can be. Successful painting is a mix of getting the right paint for the job, proper preparation of the substrate (surface), the right ambient air temperature and humidity, the proper spray equipment and air pressure and an array of federal, state and local laws. So the 3M engineered adhesives division has found a better way.

According to Tom Ihbe, market development manager at 3M Aerospace, 3M paint replacement films and tape products provide a high-performance, low-surface-energy coating replacement for paint in aerospace, electronics and other markets. Ihbe said the family of products couples the low-surface-energy performance of fluoropolymer films with a wide range of self-stick and curing adhesives construction options to meet the requirements of various surface- coating requirements.

“These coatings can be applied to a wide variety of flat and complex surfaces, including pipes, walls and aircraft exteriors. The material has been designed to adhere and conform to the substrates to which it is applied and to provide a barrier to help protect the substrate from a wide range of chemical, environmental and operational damage,” Ihbe said. “They can be color matched and are resistant to most man-made and natural elements, including acids, bases, hydrocarbons, jet fuels, petroleum, hydraulic fluids, water, blood, cleaning solvents, de-icing fluids, grease, ice and salts.”

The low surface energy of these materials is also resistant to the accumulation of contaminants on the surface. In addition, they are easily cleaned after long-term exposure to extreme environments, including salt water and high-intensity ultraviolet light exposure. The temperature service range is -65 deg F to 275 deg F, depending on application and substrate. The materials pass FAR 25.853 aircraft interior flame-resistance performance requirements, have an extremely high ignition point and do not have a propensity to spread flame, 3M said.

3M also has a removal product called the Scotch-Brite Aircraft Adhesive and Decal Removal (AADR) disc. AADR is designed to remove thermoplastic adhesives and films from many aircraft substrates. It is specially constructed of polyurethane materials for use on aluminum aircraft skins. Adhesive, decal and tape removals can be done without damaging suitable substrates, including thermoset polymers, enamel paint, lacquer coatings, some primers and aluminum alloys. When it comes to paint removal, historically the process has been almost as challenging as painting. Consider removing paint from composites.

Paint Strippers

According to Pierce Newman, technical director for San Antonio-based Eldorado Chemical, composite materials range from traditional fiberglass to Kevlar and more exotic strands embedded in a resinous matrix. “Typically, several layers are placed to create a composite panel, with each layer skewed to the next to engineer in strength,” Newman said.

“Current approaches to removing paint from these surfaces consist of sanding or the careful removal of the topcoat chemically with preservation of the primer beneath it. Older-generation paint removers based on methylene chloride and phenol are completely unacceptable on composite surfaces since once they remove the paint they aggressively attack the epoxy resin that embeds the fibers,” he said. “Within a short time, the panel undergoes delamination, meaning one sheet begins to part away from the next sheet in the panel.”

Newman said newer-generation benzyl alcohol strippers that rely on hydrogen peroxide, such as Eldorado’s PR-5044, provide operators that intend to chemically strip composite panels with a greater margin of safety than past strippers. “Airframe manufacturers are still in a flux over proper testing protocols in assessing the relative margins of safety, but first indications are that Eldorado PR-5044 is among the safest materials,” he said.

“However, while these materials appear safe on undamaged panels, there are still significant uncertainties when stripping panels that have extensive damage from nicks, gouges and other wear and tear,” Newman emphasized. “If these abrasions penetrate the first layer of the composite, they serve as channels for the solvent in the stripper to penetrate further into the composite and potentially cause accelerated delamination. The industry remains undecided on when to declare a panel too damaged to expose to a chemical stripper.”

Church & Dwight Co. of Temucula, Calif., has an alternative so safe it can be found in almost any kitchen–sodium bicarbonate. Commonly called baking soda, it is an
ingredient often used in the preparation of baked goods. It is so safe that many people use it as an instant cure for heartburn, yet it is one of the best low-impact blasting mediums available today.

“Armex [the company’s trade name for its baking soda media] is also so inexpensive that it is a one-time use media, eliminating the complex and time-consuming process of media recycling. It minimizes waste, advances pollution-prevention efforts and improves worker safety because it is non-toxic and non-hazardous.

“It is a natural, water-soluble compound that meets OSHA and EPA regulations,” Mike Doty, Armex technical specialist, told AIN. “It’s nonflammable and non-sparking, free from silicon dust and toxic fumes. It is safer than solvents and caustic chemicals and has been approved by the USDA as an ‘A-1’ cleaner.”

Doty said the media reduce cycle time for cleaning, degreasing and paint removal to one step, unlike glass beads or plastic media because no prewash is required with Armex. Also, because of its water solubility it allows complete rinsing, eliminating the risk of spent media lodging in tight spaces and critical passageways.

But of all things, why baking soda? Baking soda has a granular texture, making it suitable for use in pressure pots, cabinet systems and as an additive for pressure-washer systems. Baking soda crystals are actually sharp, so when they’re delivered under relatively low pressure but at high velocity, they will scour virtually any coating from any substrate. However, with a Moh’s hardness of 2.5 on a zero to 10 scale, with diamonds coming in at 10, baking soda will not damage most substrates. It also has a benign pH of 8.2, so it is environmentally safe in the workplace.

Armex removes dirt, carbon, grease, oils, gasket material, surface corrosion, paint and coatings from a wide variety of alloys, metals, plastic and composites without substrate damage or distortion and it leaves hard, anodized coatings intact.

Innovative Solutions

Tired of dealing with leaking B-nut connections? The engineering systems division of Eaton Aeroquip has the solution. The Aeroquip STC connector is a leak-free hose-connection system that reduces installation time, weight and, because it has a lower profile than threaded connectors do, the space required for assembly. The threadless connector simply snaps together, eliminating the need for a torque wrench. It exceeds the requirements of SAE AS1339 and is compatible with all standard aviation fluids. Eaton says it has a maximum operating pressure of 3,000 psi and a temperature range of -65 to 400 deg F.

Another finessing of technology to make a good product better is a low-maintenance nickel-cadmium battery. According to Tom Elkjer, field service engineer for Marathon Power Technologies, in the early 1950s the company introduced the nickel-cadmium sintered-plate battery for use on jets. The nickel-cadmium battery is popular because of its reliability, long life, high power output, performance at temperature extremes and low operating cost. Despite its many advantages, it does require periodic servicing.

“Because the battery will consume water when on the wing it must be periodically removed from the aircraft and serviced,” Elkjer said. “In addition to replacement of lost water, the battery is tested to ensure that it can meet any emergency energy requirements and can erase any ‘memory’ that might have developed. The need to service the battery at the required 100 to 400 flight-hour intervals has been seen by some operators as an unwanted burden and expense, resulting in their installing the old technology lead-acid batteries. The advantage is it doesn’t get serviced on-wing and needs to be replaced only annually.”

Marathon has developed a new nickel-cadmium battery called the Marathon Micro Maintenance (M3) battery that, the company claims, has all of the advantages of nickel-cadmium technology with none of the disadvantages.

“The heart of the M3 battery is a polymer-bonded negative electrode. When combined with a conventional sintered positive electrode, the polymer-bonded electrode (PBE) provides greater energy density,” Elkjer explained. “This means that the battery plates in the M3 cell are shorter than in a conventional cell with similar power output. The increased area above the tops of the plates allows for more consumable water. More consumable water equates to more time on wing between service intervals. Combined with an increased voltage plateau for the M3 cell, this means it will use less water than a conventional cell under similar conditions.”

Elkjer said the combination of more water available and less water loss typically allows an extension of maintenance intervals by three to five times, and “obviously cuts any maintenance costs by that much, which is significant especially when all of the superior performance characteristics of nickel-cadmium batteries are retained.”

The M3 battery does not require any changes to the aircraft, nor does it require any changes in battery-servicing equipment. The service intervals required for the M3 battery in corporate operations are about the same as those required with a lead-acid battery. The M3 battery is currently FAA-PMA approved for the King Air series, Bell 206 and Cessna 425, 500, 525, 550, 550 Bravo, S550, 560, 650 and 750.

Chipping In

Filter-debris analysis, a long-established process, is getting a lot of renewed attention. Mark Smith, technical administrator for Analysts Inc. of Norcross, Ga., said “chip” testing, as it is sometimes called, is not a new technology. Wear debris particles have been analyzed for many years by the aviation branches of the U.S. military. Honeywell, through its merger with AlliedSignal, maintains an OEM-certified and monitored turbine-engine filter-debris analysis program that has been in existence since 1974.

“The primary justification for debris analysis is its ability to overcome many of the fundamental limitations of conventional spectrometric oil analysis,” Smith explained. “Primarily those having to do with the particle-size-detection limits of the instruments used for metal identification in liquid oil analysis. Most oil-analysis spectrometers encounter particle-size-detection limits in oil once particle sizes exceed 10 to 12 microns (for comparison, the diameter of the average human hair is 50 to 70 microns). Unfortunately, in critical wear conditions–ones that can rapidly lead to part failure in service–wear particle sizes fall in the 75 to 250 micron range.”

The reason debris analysis is being reemphasized is increased oil filter efficiencies in both particle sizes filtered and the amount of debris that can be captured. Filter efficiency is such that it effectively removes particles of the same size that the laboratory instruments are sensitive to and searching for. As efficiency increased, oil samples drawn for spectrographic analysis began appearing cleaner without any actual change in the amount of metals that the systems are generating. So a given engine may be producing particles that get trapped by the oil filter, preventing the particles from showing up in oil samples being analyzed. The solution is to test the oil filter content, where the metallic debris is being trapped.

One of the best fuel-system-related preventive maintenance advances isn’t on the aircraft but in a contaminant filter back at the fuel farm. The problem is that the silicon-treated prefilters used at fuel farms to trap contaminants are highly susceptible to becoming saturated with water. A filter downstream of the contaminant filter extracts water from the system. The contaminant filter can become saturated by water so quickly that it may need to be changed within days of installation. At best, they require changing every 30 to 45 days, according to Ed Deyoe, hydrocarbon product manager for Parker Hannifin’s Racor Division.

Racor offers the Hydrocarbon FS Synthetic Pleated Media Cartridge to replace silicon-treated prefilters. “We have gone a year between changes,” Deyoe said. “The cartridge doesn’t absorb water, so it just traps contaminants. The water goes through and is extracted at the filter separator. The filter may be used with jet, aviation, diesel and hydrocarbon fuels and is designed for high-flow applications where long life and high-efficiency filtration are required.”

Deyoe said the cartridge offers up to four times the life of glass and cellulose composite filter elements and an efficiency of 99.7 percent of its micron rating. It is available in micron ratings of one, five, 10 and 25, and it meets the requirements of API/IP 1590 specifications and qualification procedures for aviation fuel microfilters.

Seeing the Light

An innovation considerably more visible to the crew is the liquid crystal display (LCD). Tim Rayl, business and regional systems director for advanced products for Rockwell Collins, said the company has transitioned to LCD technology for future applications. It is common knowledge that the maintenance of electromechanical flight instruments is costly and requires highly specialized technicians. The instruments must be removed for updating, modification and repair. LCD technology also far surpasses cathode ray tube (CRT) technology.

“The move wasn’t strictly for maintainability reasons,” Rayl said. “It’s true that LCDs are easier to maintain, but the primary reason for their popularity is the graphics-rendering capability and all the things it can bring to the flight-deck crew.” Rayl said prime factors in favor of LCD technology are a lower power requirement, lower weight, more capability and a larger-format display.

“Because LCDs have so much drawing area on them you can use fewer of them to present the same amount of information. That translates into fewer parts, which means the failure rate goes down,” he explained. “While we can do on fewer displays what we did before, from a human-factors point of view you also have enough room on a display to separate the information so it doesn’t have to be an unreadable jumble of images and numbers.”

Rayl also said LCDs enable engineers to do a higher level of integration from an architectural perspective. “They’re very thin and lightweight, so you have a lot of room to work with in terms of integrating electronics,” he said. “There used to be a drive box in the floorboards to drive the CRT display. Now we can put everything required in a single display box, so there are fewer parts, and that translates into improved reliability and maintainability. It also reduces the number of wires and connectors; they’re always a source of maintenance problems.”

He said Rockwell Collins’ LCD displays are as large as 10 in. wide by 12 in. tall. The common CRT size was 7- by 7-in. “We see midsize corporate aircraft and up using a four-display system, but that includes primary flight display information such as attitude indicator, airspeed, altitude, vertical velocity, flight director commands and key modes, and horizontal situation indication,” he said.

The second display is a multifunction display, including navigation map for the flight management system, TCAS, radar, TAWS and engine indication and crew alert system (eicas). “If you compared that to previous-generation flight decks you’d have a lot of panel displays, wires and connectors. Troubleshooting could be a nightmare. With LCD displays you have a central maintenance system that isolates the fault, and it’s a line-replaceable unit so you can plug in a new one if there’s a problem. And LCDs permit FLS (field load software), so you can upgrade the software in the field. The Premier I, CJ1 and CJ2 and Challenger 300 [nee Continental] were all designed around this type of platform.”

More Power to You?

The lower power requirement for LCD displays Rayl spoke of touches on an issue that has been a growing concern among the OEMs–aircraft electrical power.

In his role as vice president of advanced project development for Valley Center, Kan.-based Kelly Aerospace Engineering Group, George Massey has been promoting a 42-volt electrical system for general aviation aircraft for some time. Kelly Aerospace is a supplier of starters, alternators, voltage regulators, generator control units and alternator control units.

“For us, converting to 42 VDC from mostly 28-volt aircraft is a big plus in terms of weight reduction and performance increases,” Massey said. “We got twice the power out of the alternator with no weight increase when we went from 14 to 28 volts.”

Kelly Aerospace has also developed the concept of packaging all the electrical functions having to do with starting, generating, control, protection, distribution and annunciation into a single unit called a master control unit (MCU).

“Obviously, to make the transition to 42 volts all the suppliers of systems that use electric power must get on board,” Massey said. “So far the battery, instrument, lighting, landing gear and flaps, air conditioning and trim actuator people have all responded positively. Avionics people have been mixed in their response. Typically the marketing people seem to be guarded about anything that smells like a change. The avionics engineering people on the other hand typically feel that 42 volts would be an improvement.”

The industry is also constantly looking for ways to increase the value of the service it provides. Dassault Falcon Jet, for example, has long considered its field-service representatives (FSRs) to be a customer’s “first point of contact” for technical assistance. FSRs partner with customers in problem solving and troubleshooting. The company recently announced that FSRs would also have a “model specialist” designation, meaning they will demonstrate particular proficiency in two models specifically, as well as a general working knowledge of the rest of the Falcon family. “This will facilitate quicker technical solutions and reduce aircraft downtime,” said Ron Velivis, Falcon Jet director of field service.

A strongly emerging trend has its roots in the Rolls-Royce Power-By-The-Hour concept. For a long time Rolls was the only OEM offering a flat fee for the total maintenance of an engine, but in the past few years it has become fairly common. Most engine OEMs now offer similar programs. Raytheon Aircraft is the latest to offer a new aircraft service plan that the company claims will eliminate aircraft operators’ maintenance hassles.

Raytheon’s program, called Support Plus, provides owners of Raytheon-built aircraft with selectable options covering all maintenance issues. For a monthly service fee under a five-year contract, Raytheon Aircraft is responsible for expenses from parts and labor for scheduled and unscheduled inspections, maintenance and component removals, as well as Service Bulletin coverage. Support Plus is transferable on resale and is being rolled out for owners of new Hawker 800XPs and Beechjet 400As. Plans include expansion to include coverage of all current-production Raytheon aircraft.

It is probably a safe bet that within the next 10 years engine, airframe and avionics OEMs will all be offering similar fixed-fee maintenance programs. Meanwhile, as the demand for maintenance continues to increase, there are increasingly creative ideas emerging to deal with it.

Making the Most of Floor Space

One Mile Up of Annandale, Va., has developed Hangar Planner. It is software that takes the guesswork out of stacking a hangar or maintenance shop floor. The user can set options and preferences on a personal computer, including a layout of the available floor space. According to Gene Velazquez, a software developer for the company, the software contains 2,000 scale illustrations of commercial and general aviation aircraft. You develop a list of the aircraft and the software displays how to position them to maximize the use of space. The problem, of course, is that you are still limited to the amount of floor space you have available. Now Stevens Aviation has figured out a way to beat that problem.

Jim Amador, vice president of sales and marketing for Stevens Aviation, agreed with the need to find creative ways to maintain customers’ aircraft more cost effectively. “We see the cost of maintaining aircraft going significantly higher over the next few years,” he said. “We have to pay more for good people and their benefits, and training costs exponentially increase yearly because of both manufacturer and insurance requirements, yet insurance premiums continue to skyrocket.”

Gary Ward, the company’s service manager, said, “Eventually we may find everyone goes to the fixed-fee maintenance programs, including repair stations. Ten years ago that idea wouldn’t have been feasible, but what wasn’t feasible then may be a lot more feasible in the next few years. The thing customers need to understand is that those types of program are going to be more expensive than pay-as-you-go. What they’re doing is trading cost for predictability, and for some operations that’s an important option.”

Dick Christopher, a technical service specialist for Stevens Greenville, S.C. location, said, “On the jet side of our business the trend has been that inspections on aircraft such as Hawkers, Lears, Citations and Beechjets are getting larger because customers are adding more modifications, avionics and sophisticated interiors. What we’re striving to do is decrease their downtime, so we try to cover as much as possible in a given maintenance event to preclude having to bring the airplane back a month later for a
different inspection.”

Stevens Aviation Denver has expanded its service capabilities with a customized van it calls SAMM (Stevens Aviation Maintenance Mobile), a truck with a crew cab. SAMM was custom built for Stevens Denver, is available 24/7 and is fully equipped with parts and tools. Technicians drive SAMM to grounded aircraft in the immediate Rocky Mountain region, where they perform the necessary repairs or prepare the aircraft to ferry to Denver for additional service, if required.

“SAMM provides value to our customers because it saves them time and money,” said Craig Colby, general manager of Stevens Denver. “Instead of a customer waiting overnight for a part to be delivered we can drive there with SAMM, repair the aircraft and get the customer back in the air, often in a matter of hours.”

Christopher said Stevens has an aircraft retrieval truck at its Greenville location. “The truck accommodates aircraft jacks, toolboxes and personnel,” he said. “We get called out to retrieve aircraft that have run off a runway, have had gear malfunction and so on. We can even do on-location engine changes.”

Pay to Play

Ward pointed out one major factor in the future of maintenance: “Eventually operators are going to realize they can’t get good maintenance at the rates we’re paying mechanics today,” he said. “It doesn’t make sense to try to pay a mechanic less money to work on a multimillion-dollar jet than on a car.” A recently released salary survey of U.S. maintenance personnel indicates there has been some improvement.

The survey, which had more than 650 responses, showed that despite the economic downturn the overall average salary last year was $53,900 for aviation maintenance technicians. The same survey done two years before showed the average salary of those who responded to be $47,300. In both 1999 and 2000, it indicated that respondents believed being paid “fairly” meant a minimum wage of $25 an hour. This year, respondents’ opinion bumped that number up to about $30 an hour, or $62,400 annually. It is worth noting that many respondents worked for airlines.

While increased salary was the most commonly cited factor for improving the mechanic’s lot in life, the second most cited factor was more training. Because the FAA doesn’t regulate recurrent mechanic training many companies tend to skimp in that area, though the survey did show improvement over previous years. In 1998, 58 percent of the respondents said they received company-paid initial and recurrent training. The most recent survey indicated that number had increased to 66 percent.

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