The key to balancing hangar flexibility and efficiency in aircraft maintenance is to define the maintenance mission and provide the hangar bay design that best meets that mission.
Big, clear-span, open-box designs are impressive, and, at first glance, seem very flexible. But while those large, open hangars might provide adequate space, they likely aren't providing the accessibility to aircraft you thought you'd be getting. A clear-span design is the single most significant hangar cost driver, and the return on investment may not pay off like you hope.
Flexibility should be balanced with efficiency. Sacrificing efficient operations for flexible space is a poor trade. If that huge expensive hangar is inefficient, you have overpaid to build it and you keep overpaying in utility costs and extended maintenance turn times for the life of the facility.
Design Hangars for Your Fleet
The key to balancing hangar flexibility and efficiency is to define the mission. In general, use long spans for line maintenance and short spans for heavy maintenance in two separate hangars. While separate hangars may seem counterproductive to creating a flexible hangar, flexibility comes in the form of more efficient maintenance schedules and less risk.
Most airline fleets include more narrow-body aircraft than wide-body aircraft. Hangar space is always at a premium, and there is a greater need to get three or four narrow-body aircraft back on line compared to one wide-body aircraft. So a large, tall, long-span hangar built for wide-body aircraft that is primarily used for narrow-body aircraft maintenance can equate to a huge waste of space and money.
Mixing line and heavy maintenance in a huge open hangar raises damage risk. The aircraft in heavy maintenance is more at risk with line maintenance aircraft arriving and departing the hangar several times a day, exposing the open airframe and components to weather, windblown foreign object debris (FOD), hangar rash bumps and scrapes, and repeated exposure of workers to the outdoor conditions.
Suit Hangars to Aircraft Needs
Line and heavy maintenance operations are distinctly different in that line maintenance rarely opens the airframe to expose major internal elements and systems, while heavy maintenance opens the airframe in many locations to gain access to the major components and systems concurrently. Dwell times in the hangar for line maintenance range from an hour to overnight, while an aircraft in a C-check could be in the hangar, on jacks, for 20 days or more.
Line maintenance hangar space is defined by that mission: continuous demand for access, fast turns several times a day, or overnight. Since maintenance work is less detailed but more time critical, there is no time to set up the work docks needed for heavy maintenance. And since the aircraft types arriving for line maintenance can't be predicted, those workdocks would often be useless. But you need quick access to all parts of the aircraft. The solution is some combination of portable lifts, air stairs, and, in very high volume operations, teleplatforms.
Varying Airframes Require Open Space
Third-party maintenance providers also usually need long-span, flexible hangar space even for heavy maintenance. Those companies don't have a defined fleet like an airline. They see a wide variety of airframes and must maintain flexible space and equipment to densely pack aircraft at odd angles and shorter clearances. Portable equipment also provides the flexibility to mate to those oddly parked and densely packed aircraft. But those facilities sacrifice some efficiency for the flexibility to service the full range of airframes.
The airline heavy maintenance mission is much different in turn times, scope and intensity of work. Fleet mix is well-defined. Aircraft dwell times are measured in tens of days. The aircraft is disassembled, placed on jacks and left open for maintenance access. Efficiency is gained by using work docks that mate to the aircraft to provide access to all areas of the aircraft simultaneously. Those work docks define the hangar bay size, so extra space doesn't add efficiency.
Hangar spans can be reduced to what is needed for a single aircraft surrounded by work docks. The bridge cranes and some work docks suspended from the roof structure are heavy, so shorter spans save roof structure cost. Further efficiency is gained by customizing the hangar bay for the airframe type. The general division is wide-body and narrow-body dedicated bays, although new super-wide-body aircraft, such as the Airbus A380 and B747-8, create a new hangar class for those largest aircraft.
Know Your Needs
The key to balancing hangar flexibility and efficiency in aircraft maintenance is to define the maintenance mission and provide the hangar bay design that best meets that mission. In general, use long spans for line maintenance and short spans for heavy maintenance. Study the maintenance needs — line versus heavy — carefully, and assess the fleet size and mix, the availability of land and funding, and the needed efficiency before deciding on a large, open hangar.