May 2006 
Volume 05, Issue 1 
Commercial Airplanes

Maintaining a winner

Next-Generation 737 offers airlines flexibility from the ground up


Maintaining a winnerWhen the 5,000th 737 rolled out of the Renton, Wash., factory in January, it bore a strong resemblance to the first twinjet built nearly four decades ago. But appearances can be deceiving. The Next-Generation 737-700 model, destined for Southwest Airlines, shared few similarities with its original sibling. Smarter, sleeker and more capable, the Next-Generation 737 represents a rebirth of the world's best-selling jetliner—from its distinctive blended winglets to a new philosophy on maintenance.

That new take on maintenance reflects Boeing's strong focus on customers' needs. This approach helps make Boeing products a more attractive option in the competitive single-aisle market segment.

"Our goal was to make it fly higher, farther and faster," said David Reed, Next-Generation 737 fleet support chief for Boeing Commercial Aviation Services. "We also placed a huge focus on maintenance and reliability because it's such a big percentage of the cost of running an airline."

Typically, airlines spend 17 cents of every dollar on maintenance (see chart at right). This investment is essential to preserving an airplane's inherent safety and ensuring it performs as efficiently and reliably as possible. In an industry where profits turn on pennies, keeping an airplane flying is crucial.

To that end, the Next-Generation 737's dispatch reliability record (departures not delayed by mechanical problems) of 99.5 percent is the highest of any large commercial jetliner in the world. On the flip side, its per-hour maintenance cost is the lowest in the industry. Those two numbers make the most hard-nosed chief financial officers smile, and they're a major reason why nearly 100 customers have ordered more than 3,000 Next-Generation 737s since the program began in late 1993.

"The 737 is a great airplane," said Georg Taht, manager of aircraft reliability at Southwest Airlines, which flies the airplane model exclusively and was launch customer for the Next-Generation 737.

Taht's comment reflects the Next-Generation 737's attractiveness to airline maintenance crews. When designing the jetliner, Boeing engineers improved maintenance and reliability in part by using a software tool called CATIA. Developed by France-based Dassault Systemes, the program's solid-modeling capabilities identified maintenance access and "stay-out" zones to help ensure mechanics would have enough room around components and parts to comfortably perform inspections and other work.

How operating costs stack up

Typical Next-Generation 737 operating costs

Ownership and spares: 49%
Maintenance: 17%
Flight crew and cabin crew: 17%
Fuel: 12%
Other: 5%

Source: Boeing

Boeing also changed its maintenance program philosophy to offer customers greater flexibility. Traditionally, maintenance inspection tasks are bundled into predefined packages—called A, B, C and D checks—to be conducted at specified intervals. Starting with the 777 and, subsequently, the Next-Generation 737, Boeing led the industry with an alternative approach. As always, the company recommends intervals for each of the airplane's 883 inspection tasks. But operators decide how to package them—and benefit accordingly.

Checking igniter plugs every 1,600 flight cycles, for example, doesn't conform to standard letter checks. This task-based approach enables operators to conduct other maintenance at the same time the plugs are inspected.

"That's one of the greatest things Boeing has ever done," said Johan Kala, manager of maintenance programs for Continental Airlines. "I'm free to package the tasks where and when I need to."

The task-based approach serves a growing trend: Many air carriers prefer to conduct as much maintenance as possible overnight or while an airplane is idle to avoid taking it out of service. Towing a Next-Generation 737 into a hangar reserved for heavy maintenance can ground the airplane for several days and requires a spare to fill the gap in the airline's schedule.

Continental, Southwest and other carriers have leveraged their ability to group inspection tasks to keep the Next-Generation 737 out of the heavy maintenance hangar for its first five years after delivery. With a traditional maintenance program, the initial hangar visit would occur at 4,000 flight hours—a year or so after entry into service.

"In essence, we've given one airplane back to the airline," Continental's Kala said. That amounts to about $61 million—the median list price of a Next-Generation 737.

Task-based maintenance also enables operators to manage their resources more effectively. One European airline repackaged inspection tasks so that six mechanics can perform the equivalent of an A check overnight. Previously, the same work required 10 mechanics.

Part of that efficiency stems from grouping tasks according to their accessibility on the airplane. Given the time it takes to open access panels or reach remote locations, it makes sense to simultaneously inspect multiple items in the same area.

Improving the Next-Generation 737 didn't stop at the factory door. Boeing Commercial Aviation Services' Maintenance Engineering department—in collaboration with customers and regulatory authorities—recently completed a two-year effort to improve efficiency. Nearly one-third of the maintenance task intervals were lengthened based on in-service data provided by airlines for 41 percent of the world's Next-Generation 737 fleet.

The interval for tasks such as inspecting landing gear and entry doors, cargo compartments and the vertical fin stabilizer increased from 40 days or 300 cycles (takeoffs and landings) to 70 days or 560 cycles. "That may not seem like much of a change, but the labor and cost savings are substantial when multiplied over the life of an airplane and across an airline's fleet," said Jack Trunnell, Commercial Aviation Services director of Maintenance Engineering.

The most significant revision increased the interval for a comprehensive structural inspection from five years to six. "Besides saving nine percent in maintenance costs, the new interval keeps the Next-Generation 737 flying for another three to five days every fifth year—adding hundreds of thousands of dollars in revenue and reducing the need for a spare airplane," Trunnell said.

Fewer inspections also enhance safety, he added. Repeatedly opening access panels causes excessive wear and tear. In other cases, mechanics may inadvertently damage wires, hydraulic lines or other components while working in close quarters.

The lengthened intervals—called "task escalations"—were evaluated and approved in 2004 and 2005 by an Industry Steering Committee, a consortium of airlines, the U.S. Federal Aviation Administration and Boeing. Southwest's Taht, who is chairman of the ISC for the Next-Generation 737, said the escalations were "outstanding." He added: "The Boeing Company has done a better job of communicating information to operators and, consequently, participation in ISC meetings has risen. This gives us more service data and the opportunity to consider more escalations."

The recent changes are not a one-time effort. Maintenance programs for all commercial airplanes typically are revised annually, but the evaluation process preceding ISC approval is time-consuming and cumbersome. As more operators upgrade their computer systems, however, Boeing will be able to continuously collect more robust in-service data to analyze trends and further optimize maintenance programs.

Taht is looking forward to that day. "It will give us the opportunity to constantly improve our maintenance program," he said.

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