Most non-aviation people believe life's lone certainties are death and taxes. Those who understand aircraft operations know there is at least one more: maintenance downtime.

Regardless of an aircraft's operating environment, configuration or utilization rate, being parked for maintenance always is part of its life cycle. Such inevitability gives operators, manufacturers and maintenance providers plenty of motivation to devise strategies to take advantage of that parked time. In most cases, this means minimizing total downtime during an airframe's service life.

This is done in several ways. The most obvious one is stretching out maintenance intervals, leading to fewer heavy checks over 20-25 years. Boeing leverages its Statistical Analysis for Scheduled Maintenance Optimization (Sasmo) on its in-service fleet to find opportunities for improvement. The purpose-built tool analyzes fleet performance data and helps determine optimal maintenance intervals while minimizing the risk of in-service (and therefore more costly) disruptions.

The results can lead to big changes. On the Boeing 737NG, for instance, 80% of the maintenance task intervals originally scheduled at 4,000 flight hours were escalated based on Sasmo's findings. For the Boeing 777, Sasmo determined that 68% of the 7,500-flight-hour check tasks could be safely and cost-effectively escalated.

“These programs do not stay static,” says Farshad Doulatshahi, a program manager in Boeing's maintenance program engineering department. “The maintenance program intervals we have now for a given model are significantly different and more efficient from when the airplanes were introduced.”

Tools such as Sasmo underscore that minimizing downtime does not always mean pushing task intervals farther apart. On the 737NG, for instance, Sasmo data convinced Boeing to cut the interval times on 10% of the 4,000-hr.-check tasks. The result? Fewer in-service issues and less downtime overall.

Arguably the most aggressive effort to alter a traditional airline block-check maintenance program involves Airbus narrowbodies. In 2004, SR Technics, at Airbus's request, developed an equalized maintenance program for EasyJet's fleet of A319s and A320s to maximize aircraft availability. Work usually wrapped into 18-month C checks is divided and accomplished in overnight packages—or e-checks—at shorter intervals, typically about once every 65-70 days. Because EasyJet cannot fly at night due to noise bans, its aircraft sit idle during those hours anyway, allowing ample time for a team of 15 or so technicians to complete each e-check.

Breaking the work up into smaller, more frequent chunks allows EasyJet's airframes to stay in service for six years at a time, except for one 36-hr. check every three years and a four-day check between years six and 12 in the cycle. SR Technics says the e-check approach cuts downtime by about 28 days per airframe over each 12-year cycle that ends with a D check. For EasyJet's fleet, 157 A319s and 56 A320s at the end of 2012, that translates into a bottom-line-altering 5,964 fewer days—or more than 16 fleet years—out of service per full 12-year D-check cycle.

“We don't have any structural tasks that require long elapsed times to perform before six years in service,” explains Airbus Director of Maintenance Marketing Bert Stegerer. “All of the shorter interval tasks are system tasks, not structural tasks.”

Moreover, the e-check schedule caught or prevented problems that otherwise would have popped up during a heavy check. Fewer non-routine items and the good overall condition of the airframes meant that EasyJet's six-year checks take about 14 days, or four days fewer than first projected.

SR Technics notes that not all of the e-check metrics are positive, however. Flight-hour costs can be higher because some work must be done earlier than the optimal interval to make the program work. In addition, accessing the same area on an airframe on multiple e-checks and accomplishing few tasks each time is less efficient than opening it once during a heavy check and completing all required tasks. But, the MRO provider notes, “experience shows that these minor drawbacks are offset by maximum utilization of the fleet, the additional revenue generated and other improvements.”

Despite EasyJet's experience, no other Airbus operators have adopted the e-check concept, although other carriers have moved off of the block program. Frontier splits the 24-month, 7,500-flight-hour check into smaller packages done every 750 flight hours, Stegerer notes. In exchange for the 750-hr. checks, which are slightly longer than a routine overnight check, Frontier's aircraft avoid a lengthy heavy check for six years at a time.

Boeing's maintenance gurus report that their operators have not expressed much interest in breaking up heavy checks. Boeing maintenance engineer and 737 specialist Victor Wang notes that in the case of the popular airliner, the amount of equipment, access and downtime needed to accomplish many heavy-check tasks makes phasing them challenging. A few 737 operators roll C checks into phased B checks done every 90-120 days, but “those are very rare,” Wang notes.

Boeing 747 Maintenance Engineer Matthew Razniewski contends that the opposite is true. “A lot of operators, especially those contracting-out maintenance, will wrap smaller maintenance tasks into one single package and send it out to be accomplished in one maintenance visit,” he says. “This takes advantage of opening up access just once, doing everything in that area and closing it up once.”

Both Airbus and Boeing underscore that a customer's goals determine how a maintenance program will be set up. “Is the interest of the operator to optimize the maintenance schedule for low maintenance cost, or is it prioritizing for aircraft availability?” Stegerer asks.

Both OEMs strive to build maximum flexibility into each program, then help each operator piece together an optimal maintenance schedule. Seasonal operators will want aircraft out of service during low-demand times, while operators unconstrained by night bans may not want overnight checks to last any longer than absolutely necessary.

Boeing Maintenance Engineering prepares a report for each customer that illustrates an optimal maintenance program over a number of years. “Sometimes, an airline will put one maintenance concept in place, and a few months down the road, come back to Boeing and say, 'we've had second thoughts here,'” says Razniewski.

Maintenance programs are benefitting from the industry's natural technological evolution as well. Composites and titanium do not corrode, so heavy-check task cards for, say, an Airbus A350 will read much differently than those for an A300-600. Eliminating most corrosion issues cuts maintenance man-hours by nearly 40% on current-generation airliners compared to their aluminum ancestors, Airbus calculates.

In addition, improvements in onboard diagnostics help identify problems sooner, leading to fewer in-service incidents and shorter diagnostic times when aircraft are down for work. “Instead of tearing things down, you press a button and you get more information, so the amount of time performing a check will be less,” says Wang.

Maintenance engineering's more active role in aircraft design also is helping create better airworthiness programs. Christian Delmas, Airbus's director of maintenance program engineering, says his team's involvement in A380 design played a role in enabling the aircraft to enter service with a then-unprecedented 750-flight-hour A-check interval. On the A350, the OEM's plan is to eliminate the six-year heavy check completely, phasing much of the work into smaller, more frequent checks and moving some tasks—such as galley removal—to the 12-year heavy check.

“If we want to ensure that we have an efficient maintenance program that offers maximum flexibility to operators, we have to influence the aircraft design,” Delmas says.

One challenge presented by longer intervals between out-of-service periods is keeping up with non-critical items, such as a cabin's appearance.

Timco Aviation Services, which counts line maintenance and interiors as two of its specialties, sees such challenges as opportunities. Its Cabin LifeCare program, launched in 2011, offers interior maintenance and refurbishment tailored to an operator's needs. Day-to-day work can be done through Timco's network of 20 line maintenance stations and supplemented with “cradle-to-grave” support, either providing touch labor or supporting a customer's personnel or designated third-party providers with parts, says Leonard Kazmerski, Timco vice president of marketing and business development.

“We're able to do a little more inside the cabin than a traditional line maintenance division,” Kazmerski says.

Besides its extensive line and base maintenance service offerings, Timco produces a line of interiors products. The company's willingness to support other interiors suppliers' products as part of Cabin LifeCare underscores another approach some operators are taking to streamlining maintenance: eliminating vendors.

Lufthansa Technik (LHT) launched its Total Base Maintenance Support (TBS) offering in early 2011 with a promise of simplicity at its core. The program allows airlines to source with LHT and customize every aspect of a heavy check. “An operator with a mid-sized or large fleet has different requirements than a start-up,” notes an LHT spokesman. “TBS is offering several selectable modules for our customers and also optimizes the interfaces with other LHT Group products that the customer might have with, or will contract to, LHT.”

Most importantly, TBS offers guaranteed slot availability—thanks to LHT's extensive network, with more than 20 heavy check lines in Europe alone—combined with price certainty. TBS customers can pay by the heavy check, flight hour or month, enabling them to put off the expense of a major check as long as possible or spread out the financial burden more evenly.