March 18, 2013
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.