Each night when the lights go out at Airbus SAS in southern France, a nocturnal creature stirs.
Inside a hangar at the Toulouse production campus, the planemaker’s “iron bird” performs all-night tests on hydraulic pumps, electrical cabling and mechanical parts draped across a loose layout of the A350 jetliner. When Airbus engineers return the next day, they sift through the data to fine-tune the new wide-body’s systems ahead of its maiden flight later this year.
In an era when design and evaluation is done mainly by computer, the iron bird harks back to the mechanical dawn of the aviation age. With aircraft becoming ever-more complex, Airbus says it’s a vital step in spotting issues which might otherwise go unnoticed -- like the wing cracks that blighted its A380 superjumbo and battery faults that grounded Boeing Co.’s 787 Dreamliner a year after the marquee model had entered service.
“We’re good at analyzing things like the aerodynamics of structures, but when you get to very complicated systems it’s hard for computers to predict the interactions ahead of time,” said John Hansman, professor of aeronautics and astronautics at the Massachusetts Institute of Technology. “A lot of things don’t show up until you start hooking the pieces together.”
Airbus has budgeted 11.6 billion euros ($15 billion) to develop three variants of the A350. The iron bird, housed in a 2,400 square meter hangar 10 minutes from the final assembly line, took 100 people to build but requires no more than 10 to work it. A central catwalk and two flanking balconies offer vantage points for engineers to monitor developments.
About half of a modern aircraft’s value lies in systems that control everything from the movement of wing surfaces to landing gear and braking. The iron-bird approach has helped Airbus identify multiple improvements to hardware and software, now incorporated into equipment on the test bench, according to Mark Cousin, head of system-integration tests for the A350.
In one case, the plane’s landing-gear doors failed to open smoothly, a malfunction that was fixed by changing the time delay between releasing the hatches and applying the hydraulic pressure required to open them, he said.
Airbus has built other physical mockups of the A350, with the so-called cabin zero platform in Hamburg used to test items such as crew-rest areas, galleys, toilets, air-conditioning systems and inflight entertainment.
The manufacturer has employed iron-bird test rigs from its inception, starting with the A300 in the 1970s.
The A350 rig has been in use since 2010, well before the first plane even began construction. Initially it ran with generic industrial parts, with a gradual switch to real components as subcontractors ramped up production.
Airbus’s new wide-body is being developed to challenge the 787 and Boeing’s best-selling 777, now 20 years old. Two planes have been built so far, one for static testing, the other a flyable model, with a third now under construction. Qatar Airways Ltd. is due to initiate passenger services in late 2014.
While most of the A350’s innards are replicated on the iron bird, Airbus has complementary setups in Filton, England, for landing gear -- among the plane’s largest and most complex structures -- and in Bremen, Germany, for wing surfaces. Both sites can be connected to the Toulouse test-bed via computer.
“This has become ever-more important given the complexity of computer-based aircraft systems,” said Hans Weber, president of San Diego-based consultancy Tecop International, who has advised the U.S. Federal Aviation Administration. “The codes run to tens of millions of lines and it’s necessary for proper system debugging and integration, before you actually fly.”
Boeing has similar test facilities, though it didn’t use an iron bird until the early 1990s for assessment of the 777. Prior to that, avionics, engine and flight controls and mechanical, electrical and hydraulic systems got their first integrated workout only during ground testing of the actual plane.
For the Dreamliner, Boeing didn’t build an iron bird, and instead created a “virtual” plane spread out among labs connected to one another via computer. That allowed engineers greater integration with the far-flung network of suppliers.
The A350 iron bird paid special attention to lithium-ion batteries like those that failed on the 787, which Airbus, too, had planned to use. Though the test bed didn’t reveal any problems, the company decided to switch to more traditional nickel cadmium battery packs to avoid the risk of program delay.
No matter how rigorous the tests, there are still surprises when a plane leaves the ground.
Most come during flight testing, which for the A350 will span about 12 months, early enough for designers to make changes before serial production. Others may not surface until a plane enters service. The A380 debuted with Singapore Airlines Ltd. in 2007, yet cracks caused by a poor choice of material for a small structural part took four years to appear as fatigue set in.
In some cases, malfunctions result from exposure to very high or low temperatures. While extreme heat or cold can be simulated on the iron bird for specific component, it’s not possible to run checks on the entire plane. Neither can testing predict the range of human error that can affect an aircraft.
“The people operating an iron bird or a test plane know how it works so they don’t tend to misuse it,” says Hansman. “In the real world someone drops something or just hooks it up wrong.”