Maintainability is now the buzzword in aircraft design

 - May 6, 2008, 6:41 AM

The longer you’ve been around business aviation, the more you’ve witnessed the revolution in the way manufacturers approach the long-term reliability and maintainability of their aircraft. The shrinking maintenance force, combined with the tightening of corporate budgets, is putting the squeeze on OEMs to deliver more capable, reliable and cost-effective aircraft.

“In the past it was tell the engineers what you want, put them in a room with a piece of paper and a stack of money and they would design an airplane,” Greg Graber, director of light jet technical support for Raytheon Aircraft, told AIN. “Once the aircraft was designed and flight tested, you’d throw it over to manufacturing, then they’d throw it over to the field to let the techs and mechanics figure out how to work on it–there was very little thought ever given to ongoing maintainability.”

In today’s world of business aircraft, that type of thinking has gone the way of the radial engine. Said Joe Hepburn, manager of product marketing for the Citation X, “When we started developing the Citation X, it was the first opportunity we had to start with a clean sheet of paper. We weren’t ‘grandfathering’ from another Citation model. It was a brand-new design, so we had the luxury of using some fresh ideas.

“The Citation X ushered in a level of performance and sophistication that was not only new to Cessna, but to the entire industry,” he added. “And we didn’t want to forsake the reputation of the entire Citation family. We knew the Citation X would be a challenge to operators if we didn’t take the next step with designing in maintainability, maintenance access and diagnostics.”

Designing for the Customer

In the development of their newest offerings, all of the OEMs have done more than create a new generation of high-performance business jets, they have ushered in a new era of company-customer design cooperation.

“Eleven years ago, the concept of an ultra-long-range business jet was something very new to all operators,” said a Bombardier spokesman. “Long before we even announced the project we were talking to and gathering information from current customers and prospects to see what they would want in this new type of aircraft.”

Like anything, when you ask operators what they want in their next airplane, they figuratively ask for the moon and it was up to members of each manufacturer’s in-house development team to figure out what would and wouldn’t work. “Two people from my maintenance group worked on the Premier I project full time for two-and-a-half years,” Raytheon’s Graber said. “They were with the engineers during every step of the design review to figure out the best way to do things– down to where to use screws instead of rivets for easier accessibility.”

Cessna’s Hepburn said, “When we assembled our ‘Team X,’ we did so from a long list of people who already operated our aircraft, as well as some large corporate models. The more varied their fleet, the more they had to offer. During the design process, we had these people come to Wichita and give us input and guidance on a quarterly basis. By far the main message they kept giving our engineers was ‘make it easy to work on.’”

“Increasing dispatchability means giving technicians access to the various components on the airplane in the shortest possible time,” he added. “Once they have access, they also need to be able to change or repair the part with the minimal amount of operational testing and rerigging. Our customer representatives were extremely helpful in these areas.”

With many of today’s new-generation jets being clean-sheet designs, engineers have had numerous opportunities to help control the ongoing maintenance costs of these new airplanes. “One big complaint we heard from mechanics was the location of the aircraft’s battery,” Graber said. “Why did we always put such a heavy thing in such hard-to-get-to locations? Now the Premier I has its battery right behind an exterior access door. Just open the door and lift it out. It’s a little thing, but it’s a big help to mechanics.”

“Very early on in the design process of the Learjet 45, we had input from a large number of Lear operators to draw on,” said Steve Crowford, Learjet’s v-p of technical services for business aircraft. “It was a big benefit to the end customer. For example, we were able to direct the designers to improve the accessibility to the line-replacement units that will need periodic inspection and maintenance.”

In older business jets, accessing the various components, such as hydraulic lines, control cables and electrical wires that run from the front of the aircraft to the back, often requires removal of major cabin components. This not only requires time, it also increases the chance of damaging the expensive upholstery and woodwork.

In the design of the Citation X, Cessna’s team took a new and more logical route: they kept these systems outside of the pressure vessel. “Now all of these things that you have to go in and look at are in places where they are easy to get to,” Hepburn explained. “No more removing seats, cabinetry and carpeting to see what’s going on. Just open one of the many panels on the belly and you’re there.”

Another suggestion from the “collective wisdom” of the members of Cessna’s Team X was, while they are going to reroute the systems outside the pressure vessel anyway, why not orient the systems in a new way, too? “What they suggested was to run the hydraulics along the bottom of the fuselage so if they leak, fluid is not running down the inside of the cabin. Then put the control cables and electrical on the next level up, followed by the bleed-air lines on the top,” said Hepburn. “It’s a simple and effective solution to a long-standing problem.”

“One way we have made the Learjet 45 easier to work on has been to reduce parts count in some components by more than 50 percent,” explained Scott Wight, Learjet model 31A, 45 and 60 product manager. “An example is the forward bulkhead. By milling it out of a solid piece of aluminum instead of assembling it the old way, we’ve reduced 80 parts down to one.

“Another seemingly simple thing we did was to replace all of the interior lights with new LED units,” he added. “They offer a number of significant advantages. They’re a lot cooler, and with a life expectancy of 10,000 hours they will literally never have to be changed during the operational life of a Model 45. It’s a small thing, but it can save an operator time and money.”

“Since the Model 45’s introduction we’ve been on a rigorous task-escalation program that is reducing the number of items needing to be inspected at each given maintenance interval,” explained Peter Levy, Learjet’s supervisor for logistics and support equipment. “For example, a 300-hour inspection used to take a couple of days to complete. Today, that’s been reduced to what amounts to a glorified walkaround. You can complete it in a couple of hours. Compared to older-generation Learjets, the 45 is a very simple, maintenance friendly
airplane.”

Just Tell Us Where It Hurts

The monitoring and diagnostics capabilities of today’s advanced integrated avionics systems have played a big part in the manufacturers’ abilities to help technicians shorten the maintenance path. “We’ve tied the avionics into the airframe in several areas and integrated it so that we can go back and look at what’s going on,” Graber added. “We worked closely with our avionics and system suppliers to develop fault codes to help us troubleshoot the airplane.”

“With the Citation X we created a very sophisticated machine, but we couldn’t afford to have it require tons more time and effort to troubleshoot,” Hepburn explained. “We decided to take advantage of that sophistication and use the information to help technicians go in and quickly diagnose a problem and come to a solution. Of course, we’ve encountered people along the way who are deathly afraid of electrons.”

Once a crew squawks a fault message, it’s up to the technician to find what caused that message–easier said than done. “The EICAS system on the Citation X can display upwards of 225 different messages as opposed to just a blinking annunciator light,” he said. “But as informative as those messages are, they are just the top level of the information a maintenance tech needs to correct the problem. The logic modules were created to deliver that next level of information.”

To meet its customers’ needs to have optimum dispatchability as it travels the world, the designers of Bombardier’s ultra-long-range Global Express pioneered a number of mechanical and technological advancements. “Probably the one that’s most obvious is our central aircraft information and maintenance system (CAIMS),” said Marc Bouliane, Bombardier’s director of Global Express programs. “It was developed specifically for the Global Express’ mission profile. CAIMS lets operators access information on all major aircraft systems down to the LRU level. And it delivers those reports in plain English.”

Because the Global Express will give operators access to destinations where spare parts may be difficult to come by, Bombardier has given the flight crew a tool to help diagnose problems in flight. “There’s an option called ‘in-flight CAIMS,’” said Daniel Vinet, Bombardier’s manager for customer support for the Global Express programs. “If a crew gets an in-flight fault message, they have the capability to print out a detailed report of what the CAIMS has detected. The report will tell you which component has malfunctioned so the crew can contact their base or Bombardier or whomever to have a replacement part dispatched to their next destination as soon as possible. It will really help improve the aircraft’s reliability and dispatchability, especially when operating in remote locations.”

Vinet also said that the CAIMS system permits direct access to all of the aircraft’s publications, including maintenance manuals, Service Bulletins, illustrated parts catalog and wiring diagrams to help make required repairs away from base easier. “The CD-ROM-based information system will show you exactly where the part is located, how to access it, how to change it and how to test it–all without having to go and look through stacks of binders.”

While the various built-in monitoring, reporting and diagnostics capabilities found in today’s new-generation aircraft can provide a technician with a mind reader’s insight into an airplane’s internal workings, make no mistake that they are no substitute for training and experience.

“No matter how sophisticated an airplane is, it isn’t going to do all the work for you,” Lonnie Williams, FlightSafety International’s corporate counselor for maintenance training said. “Let’s say you fix what the airplane told you was wrong and it still doesn’t work. Then what do you do? You are still going to have to fall back on your skills as a technician to figure out which box went bad.”

“Although we’ve done a lot to incorporate diagnostics to help the technician, it’s no substitute for type-specific training,” Graber added. “A lot of the systems are combinations of components so you really have to understand how they work to use the diagnostics as intended.”

“Years ago people would say getting an A&P was a ‘license to learn.’ But today it really isn’t,” Williams said. “These airplanes and systems are too sophisticated and expensive to allow someone to ‘bump their heads’ learning how they tick. There are just too many paths to follow when you’re troubleshooting a problem.

“FlightSafety has been involved on the front end of the development of many of these new airplanes,” he added. “The OEMs have brought us in right from the get-go to get a heads-up on where the design is going so we can get started on developing the training. Also, as the airplane matures, so does the training.”

“We’ve even gone so far as to change our philosophy on how to create maintenance manuals,” Graber explained. “Today, volume one is system description and operation. Volumes two and three have all the troubleshooting information in them. So that guy who is training over at FlightSafety is going to be training right out of the Raytheon book they will use in the field from the very first day. There is no separate training required to relearn on the floor what you learned in class.”

Is the increasing sophistication of the built-in monitoring and diagnostics capabilities of the new-generation of jets going to usher in a change in the way technicians work? A growing number of operators seem to think so. “A lot of our customers want us to increase our training for troubleshooting and dispatching aircraft,” Williams said. “With the built-in diagnostics as a foundation, what used to be a 60-minute go/no-go decision window is shrinking to 30 minutes. So for many operators, the responsibility of whether or not an airplane flies that day rests squarely on the shoulders of the technician. It’s not just being a ‘wrench turner’ anymore. Today, you are a proactive manager of each aircraft’s situation.”