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787’s maintenance team makes the most of delays

 - November 11, 2009, 11:45 PM

While no one at Boeing would dare admit to any level of satisfaction with the two-and-a-half years of delays to the 787-8, the program’s chief mechanic, Justin Hale, might be one of the few people within the company who can say it has helped make his job easier.

“Certifying a maintenance program and getting all of the data transmitted to the FAA, transmitted to the industry steering committee, analyzed and settling on certifiable intervals is always a challenge when you’re putting a new type into service. And you always feel rushed to get that done,” said Hale. “And the nature of this industry is if you don’t feel like you have enough time to analyze something thoroughly, then you err way on the side of caution.”

When the 787-8’s maintenance steering committee–consisting of 26 airlines, 12 suppliers and representatives from eight regulators from around the globe–first submitted the then-final data for certification in the fall of 2007, the U.S. Federal Aviation Administration and European Aviation Safety Agency (EASA) wouldn’t accept 400 of the 760 maintenance intervals the group recommended. After 62 weeks of meetings over the span of three years, in fact, the agencies rejected most of its recommendations for insufficient data.

“If the airplane had been on time we likely would have certified the maintenance program right there with shorter intervals for those 400 tasks,” Hale told AIN. Of course, much of the caution exhibited by the regulators lay with the fact that no in-service history existed for such a radical new design–distinguished by nearly exclusive use of composite materials in the fuselage and a so-called “more electric” systems architecture. As things stood, the group had already considered its recommendations highly conservative. To Hale’s disappointment, the FAA, in particular, wanted more analysis before it would accept most of the proposed intervals.

As the program continued to confront delays, however, Hale and his team could revisit the recommendations, resubmit data with more robust analysis, provide more data to the FAA, EASA and the steering committee and ultimately gain approval for all 400 of the original intervals on Dec. 16, 2008. “I don’t believe that there’s a single interval that we ended up pulling back from our recommendations with all that analysis,” said Hale. “That never would have happened if we didn’t have that additional time.”

Now working with his maintenance operations team primarily on the 787’s next iteration–the -9–Hale said the company will use the next variant as a “weight-reduction block point,” meaning they’ll need to ensure that any weight-reduction efforts don’t compromise the maintenance guarantees set by Boeing.

Low Maintenance Costs Guaranteed
For the first time in its storied history Boeing will guarantee to every customer that an airplane will cost a given amount less to maintain than the airplane it replaces. In this case, the OEM guarantees at least a 30-percent reduction in cost compared with the 767-300ER, said Hale. “That number varies from customer to customer and gets tweaked a little based on their operational profile, but I don’t recall seeing a number lower than 30 percent,” he said. Those numbers also don’t include any separate guarantees issued for the engines, which, of course, contribute significantly to the overall maintenance burden.

Boeing expects to meet its own commitments primarily by eliminating and lengthening maintenance intervals, the most obvious involving its mostly composite airframe. The move away from aluminum, said Hale, means the time between some of the same structural checks will increase from, for example, six years in a 767 to 12 years in a 787. “So right out of the gate you’ve cut your structural maintenance burden in half,” he said.

Meanwhile, the 787’s composite and titanium floor structure eliminates the chronic corrosion that aluminum floors routinely show. “We have actually been able to show to the satisfaction of the regulators that the in-service performance of the 777 floor, which also is carbon fiber, has been so outstanding that we no longer have a directed, specific inspection at any point in the life of the airplane, where we have to go in and look at the floor,” said Hale. Rather, 787 operators will get credit for a floor inspection while performing so-called “enhanced zonal” checks covering wiring or brackets, for example. In an aluminum airplane, such as a 767, explained Hale, the majority of the floor needs to undergo inspection every six years, while areas more prone to corrosion get checked every three years.

Although composites fatigue, they do so in a manner and at a level that “basically moves fatigue out of the area of consideration,” said Hale. “It’s not even an issue at the kinds of loads we put into the airplane.” Rather, engineers base sizing of composite structures on the likelihood of accidental damage such as a bird strike, for example, or a wayward jetway.

Boeing believes the 787 will require 54 percent fewer scheduled maintenance hours than the 767 needs over the course of 20 years. Not all of that benefit comes from the use of composites, however. Equally fundamental changes to systems accounts for much of the reduced burden as well. Most notably, perhaps, a move away from hydraulic and pneumatic systems to electric systems with fewer moving parts stand to drop life-cycle costs dramatically, said Hale. 

For example, rather than using hot air blown out through a series of ducts onto the leading edge of the wing, the 787’s electrical anti-ice system uses a kind of heating blanket sandwiched between the wing slats and the erosion shield on the front of the slats. While a failure in a pneumatic system generally means an entire wing loses its anti-ice capability, the fact that the 787’s electrical system controls a series of heat zones on the wing’s leading edge means that more often only a small portion of the system will fail.

“In the 787–and really we see this in a lot of areas in electric systems, including brakes and the wing anti-ice systems–when there are failures, they happen in a very compartmentalized and limited fashion because, for example, each slat on the 787 is divided into six electrically heated zones and the most common failure mode is just to lose one sixth of one slat, which the airplane is indifferent to in terms of icing.”

Electric Brakes Less Complex
Meanwhile, benefits derived from the switch to electric brakes include reduced mechanical complexity and the elimination of potential delays associated with leaking hydraulic fluid, for example. Designed to incorporate four independent brake actuators per wheel, the modular system will allow operators to dispatch with one actuator per wheel not working. Another potential benefit includes the electric system’s automatic wear-monitoring function. With a typical hydraulic system, the operator must turn on hydraulic power, send a mechanic into the flight deck to step on the brakes while another mechanic examines a pin at the wheels that shows how much wear has occurred. The 787’s electronic monitoring eliminates that need, although the FAA still hasn’t yet certified the system. “We need a little bit more experience with the system before the FAA will allow us to use that in lieu of physically going down and looking at the brakes, but that’s a good example of eliminating a maintenance item,” said Hale.

“And we’ve got numerous areas where, for example, previously we would have to test a valve operation in the wing anti-ice system functionally; we would have to apply pneumatic power, electric power and hydraulic power on the airplane, and actuate a valve to verify the functionality of a system that’s difficult or impossible to monitor automatically. Now the vast majority of those checks have been automated. They’re completely transparent to the flight crew and if there is a failure we’re detecting it so much sooner than we would on a conventional airplane. We don’t even have to make the pilot aware of it in most cases.”

Of course, the “more-electric” architecture comes with a price–namely, need for a liquid cooling system that itself can need maintenance. The cooling system applies generally to all the high-power electronics on the airplane–essentially all the power conditioning elements, explained Hale. Electrical power entering the airplane from the generators needs conversion into different kinds of power for use by different systems. That level of power conversion for some of the larger loads, such as cabin air compressors and hydraulic motor pumps, generates excessive heat. The cooling system, which essentially pumps fluid through those components, consists of a heat exchanger in the ram-air circuit of the airplane and a pair of redundant pumping systems. Scheduled maintenance consists essentially of replacement of the fluid, while failures of any of the pumps or other components of the system could require unscheduled repairs. 

“The way you allow maintenance to go into an airplane is that you have to prove that it’s a positive trade in some other way,” said Hale. “So you’re getting a net benefit somewhere…The good news about the liquid cooling system is that it’s largely transparent to the pilots and even to the mechanics.

So, for example, if you were to change a component in the system–let’s say a large transformer rectifier unit–you can literally change the box the same way you would change an avionics box. It simply slides out of the rack and a new box slides in and all of the liquid connections are integrated into that removal and installation procedure.”  

On-Board Maintenance System
The benefits of “transparency” perhaps most plainly reveal themselves in the 787’s on-board maintenance system, largely derived from that used on the 777 but expanded in scope by some 40 percent, said Hale. That expansion of capability encompasses not only faults that require immediate attention, but more of what Hale called “economic-level” faults, which if addressed sooner rather than later can mean the difference between performing a straightforward overnight task and taking an airplane out of service.  

Meanwhile, Boeing has integrated its on-board maintenance system with its support information, including items such as the airplane maintenance manual, the airplane fault isolation manual, the structural repair manual, pilot and maintenance logbooks and parts information. With such integration, a mechanic can use a wireless laptop to trace faults, initiate functional tests, access the maintenance manual, load data and essentially have access to all the information and capability he or she needs to compete a particular task.

Hale cited as an example a flashing “generator-on” light but no generator failure. In such a case, the problem could reside with the switch, the light in the switch or perhaps with a loose wire. Of course, the pilot would have to log the problem in his pilot report, which on the 787 gets performed electronically. “The electronic logbook is integrated with the electronic flight bag, so the pilot can actually pull up an image of the flight deck, indicate the area where he saw the problem and link his pilot report with the things that the onboard maintenance system is noticing,” said Hale.

That capability, he explained, proves particularly critical because when a mechanic gets handed a pilot report–historically a hand-scratched piece of paper–often he or she doesn’t get enough information to troubleshoot the problem.

But by linking what the airplane itself knows with what the pilot saw, the system connects two key components. Finally, because of the integration of the support information with the onboard maintenance system, the mechanic can use the laptop computer to link directly from that fault to the fault isolation manual.

From the laptop, the mechanic can initiate functional tests, access the airplane maintenance manual to refer to a particular procedure and load data. “Every piece of support information and every piece of airplane information has been consolidated and made available on this single device, which can be taken outside the airplane, taken right to where the work is being performed,” noted Hale.

“Having worked in the field as a mechanic I know that you’re always running from one place to another, either to the airplane to reference something that the airplane can tell you or back to the library to look up a new procedure that’s been cross-referenced out of the fault isolation manual,” he said. “And you end up doing a lot of jumping around to different locations and different information sources to get all the pieces of a puzzle before you can come to a conclusion to fix an airplane. Our goal was to consolidate all that information into one resource.” 

In fact, the 787 maintenance laptop also is capable of controlling circuit breakers, running airplane system tests, rigging flight controls, installing software parts to the airplane and performing many other functions, all remotely via a wireless connection to the aircraft.

Of course, Boeing’s wider goal centers on delivering an airplane that can save its operators time and money, and Hale’s team appears to have done its part and more. Unfortunately, the many delays to first flight have led some of its customers to question to what extent Boeing can, in fact, deliver on its promises. Time will tell for sure when the airplane finally does enter service. Until then, Hale can talk only about the 787-8’s potential and continue work on the -9 while the airlines wait– patiently in some cases, not so patiently in others–for all the technological wizardry to pay dividends.