Sunday, June 1, 2003
Airbus A340: Smart Design
"On the A330/A340, Airbus has put efforts on simplifying maintenance right from design," said Régis Boniau, Air France manager, A330/A340 fleet. Airbus engineers are working on this even earlier in the design of the new A380, he added.
Fly-by-wire technology on the A330/A340 family, and a long-time Airbus design feature, has contributed to make maintenance simpler. "We have no longer to set cables and it is much more reliable," Stéphane Tessier, line maintenance technician, explained.
Michel Eveno, A330/A340 technical manager, added that "engine controls have improved, too. We do not have to set the engine’s zero thrust point any more," he said.
Air France Industries has found that maintenance effort is cut in half when comparing the A340 to the older A310. "Line maintenance requires three persons instead of six," Tessier said, even though the A340 is much bigger than the A310.
Another aspect of maintenance that is improving is engine monitoring, Boniau said. "The high cost of engine removals has sparked a trend toward longer time on wing; thanks to smarter engine monitoring and inspections, there is sustained progress." On the A340, for example, parameters are easier to analyze, and this makes it easier to determine the right time to remove the engine, avoiding unnecessary early removals.
Commonality between the twin-engined A330 and the four-engined A340 is a major benefit, too, Boniau said. These are two different aircraft with distinct seating capacities and ranges. Still, the difference between the two translates into just a 10-day difference in terms of training. "The bigger difference is in the engines," Tessier said. The A340-300 is powered by CFM56-5C turbofans, whereas Air France’s A330s are equipped with General Electric CF6-80E1A4s, the latter being much more powerful. ETOPS (extended twin-engine operations) qualification for the A330 also implies more frequent checks and training.
Safety margins used to be more conservative, but the experience the manufacturers build on now allows them to reduce those margins, Boniau pointed out, while preserving plenty of safety. This obviously has a nice translation into lower maintenance costs.
Our three Air France specialists insisted that, in spite of easier maintenance, human expertise remains necessary on the modern Airbuses. For example, Tessier said, "when we use a borescope or when we determine whether tolerances are fine."
"Thanks to the replacement of paper manuals by CDROMs, we spend less time looking for the cause of a breakdown," Tessier told Aviation Maintenance. "Electronic documentation, such as the troubleshooting manual, allows us to save 20 percent of time when compared to what we do on older-generation aircraft such as the A300/A310," he continued. Access to documents on the Air France computer network allows navigation with keywords and hypertext links, which technicians find to be very convenient.
Today, at Air France’s Charles-de-Gaulle airport base in France, the troubleshooting manual can be consulted in a library, which is in order to ensure it is up-to-date. Airbus offers on-board, electronic troubleshooting manuals as an option, but Air France did not opt for this feature as it makes updates more difficult. The next step is, Boniau said, "a wireless radio link to make it possible to have up-to-date manuals in our ground vehicles." Electronic documentation does make updates easier. However, "Airbus wants to offer online updates but this would be incompatible with our system," Boniau said. Air France Industries’s single system makes Airbus and Boeing electronic documentation available on the same system.
Centralized maintenance computer–Airbus
A significant step forward for Airbus maintenance is the centralized maintenance computer. "Formerly, built-in test equipment was scattered and you had to work on several computers on the aircraft," Tessier said. Now the CMC gives comprehensive information (including history of parameters) in plain English. Some pieces of information are in hexadecimal format but "these are very specific details that only the manufacturer is interested in," Boniau added.
Datalink via the satellite-based ACARS system allows real-time monitoring of in-flight aircraft. Data are received in Charles-de-Gaulle and forwarded to other bases if necessary. "This way, we can anticipate what kind of maintenance equipment and spare parts are needed at the next stopover," Boniau said. Sometimes, experts can even find a solution that can be performed during flight. "This is often a reset of the system," Boniau said.
Monthly technical follow-ups are available from Airbus, along with operator symposiums. Airbus also receives feedback from operators through usual tools such as hotlines and operator symposiums.
We asked about what kind of future improvements maintenance people are hoping to see in Airbus aircraft. Eveno answered that in the future, he hopes an ever-more integrated avionics suite will avoid the coexistence of conflicting software. "When you replace some out-of-order equipment, non-certified configurations can appear in the aircraft and sometimes computers have difficulties in communicating," he said.
"Different versions of software can sometimes be incompatible with the existing configuration; today, the aircraft is unable to detect this kind of problem," Boniau added. Easy access for usual inspections is also a major concern.
Like many airlines, Air France has been much involved in Airbus’s working groups for the new A380 550-seater, the first flight of which is pegged for 2005. The aim of the working groups is to find compromises that take into account, as far as it is possible, maintenance technician requirements. "The bigger the airplane, the heavier the parts and equipment," Eveno stressed. Which means the job can be more laborious.
For instance, "an actuator that weighs 33 pounds on an Airbus A330 or A340 can have a 100-pound equivalent on a Boeing 747," Boniau said. Parts and equipment that are located in high areas are thus difficult to handle, too.
"On the A380, we may have to remove 220-pound servo-controls from the tailfin," Eveno added. This should imply specific tools.
The only area where the trend is towards more complicated maintenance is in the cabin, according to Boniau. "In long-haul aircraft, as seats become more comfortable and get more in-flight entertainment systems, they need more maintenance," he said. "Though in operation, some of these systems are not mature; the consequence is we cannot keep their maintenance costs under control," he explained.
Some maintenance aspects that have not changed are structural inspections. "This is still a physically tough job," Tessier said.
Boeing 777: Maintainability
The 777 is the first Boeing aircraft that complies with the MSG-3 standard (Maintenance Steering Group, 3rd edition). These standards have been successively developed by the industry to create more efficient maintenance programs, by analyzing failure modes and their level of criticality. "MSG-3 reduces the number of items to check," said Raymond Topin, Air France Boeing 777 engineering and maintenance manager. On the 777, some 20 items are checked on a periodic basis, against 200 on the 747-400. According to Topin, the latter is not a pure MSG-3 design, as it is derived from the MSG-2 747 Classic.
"MSG-3 starts with asking: what is the function of the item? It then takes redundancies into account; for instance, the landing gear hydraulic system works at every flight, so periodic checks are performed on the electric backup system only," Topin explained. In other words, MSG-3 does not focus any longer on the piece of equipment itself.
Inside the 777 cockpit, on the right side, a centralized maintenance computer workstation is dedicated to ground maintenance. "You can perform tests from this workstation," Topin said. He said this direct link to the centralized maintenance computer is highly user-friendly.
Regarding day-to-day maintainability, Marie-Pierre Lavigne stressed that Boeing has taken into account requests from the airlines during the design phase. "This makes accessibility on the 777 better than that of the A340, with for instance one large hatch instead of several small ones," she said.
When compared to the 747, the 777 requires three times fewer man-hours for light maintenance. And it is not three times smaller; standard configurations are respectively 416 and 305 seats.
On a 777, a D-check represents 6,000 hours versus 35,000 on a 747. "This is two weeks versus five," Topin told AM.
Centralized Maintenance Computer–Boeing
"The 777’s centralized maintenance computer makes it an aircraft that talks and says what symptoms it has," Topin said. The information it gives is relevant, too. "There are much fewer nuisance messages given to the pilot and the maintenance technician," he said. In this regard, the 777 is fully MSG-3 standard whereas the 747-400 and the 767 represent only the outlines of MSG-3 standards. The software delivers alarm messages that are based on a difference between the current value of a parameter and its nominal value. There are sometimes transients such as very short cut-offs that cause nuisance messages, Topin said. On the 747, a time-delay was introduced, which has reduced the number of nuisance messages. The pilot or the maintenance technician detects the few remaining nuisance messages by checking that some other parameters are okay. On the 777, there are almost no more nuisance messages.
According to Topin, there are a lot fewer nuisance messages on the 777 than there are on A330/A340s.
In flight, the centralized maintenance computer displays alarm messages in the cockpit only if the crew needs to be informed.
"Non-flight-deck-effect alarms cause the system to look for co-related parameters and send a telex to the ground staff via the ACARS datalink," Topin explained. This allows people at the Charles-de-Gaulle base to call the mechanics at the next stopover. The latter prepare the required tools and material for the repair, if needed. In addition, all these messages are stored in a 30-month rolling database for back-office analysis. "We have to keep an eye on intermittent messages, as they can become ‘hard’ ones," Topin said. This is different from trend monitoring, where engineers follow wear parameters, he clarified.
Progress made on the 747-400 (versus the classic 747) against structural fatigue has been carried through on the 777. "The 747-400 is designed for 20,000 cycles [Air France statistics show a daily utilization of 1.7 cycles]. At this point, it becomes too expensive to maintain and we phase it out; the 777 is capable of 32,000 cycles, which we normally will never reach," Topin explained. Composite materials have been part of the progress, along with titanium in wet areas that are subject to corrosion, such as those under toilets and galleys, he said. "There, we had to perform difficult checks every four years; now we do not have to do this any longer." However, titanium is heavier.
The downside of composites, both Airbus and Boeing maintenance managers said, is that inspections are difficult. "Delaminations are difficult to detect and impossible to control," Topin said.
Monthly technical follow-ups are available, along with operator symposiums. In addition, Boeing allows direct contacts between operators through electronic discussion forums.