Aircraft Manufacturers Need to Consider Risk of Injury in Manual Material Handling Tasks
Wheels move all types of things in all types of places. There are some unique situations involving manually handling wheeled objects in aviation, both in manufacturing and in the operation of commercial aircraft. There are risks of overexertion injuries resulting from pushing and pulling when the tasks are not well designed, controlled and managed.
Using Liberty Mutual Tables to Evaluate Material Handling Tasks and Reduce Risk of Injury
One example from Malaysia describes an analysis of the risk of overexertion injuries while manually moving carts in an aviation manufacturing facility. The task involved male operators moving carts carrying 500 kg components about 2.1 meters every 45 minutes throughout a 12-hour shift. The Liberty Mutual Manual Handling Tables were used to evaluate the push and pull forces and it was determined that only about 50 percent of male operators could exert the initial and sustained forces required to move the carts. Although some men could move the carts, they are at risk of injury. Liberty Mutual researchers have found that maintaining push and pull forces at or below a level achievable by at least 75 percent of females significantly reduces the risk of injuries.
Conversations with ergonomists and engineers in aircraft manufacturing facilities in the US emphasize the variety of things on wheels that are pushed and pulled. They range from supply carts to scaffolds used to access large aircraft as they are assembled. However, whatever the object moved, the Liberty Mutual Tables are commonly used to evaluate the acceptability of the required forces.
Ramps Used in Aircraft Manufacturing Increase Force Required for Manual Material Handling
One vexing problem associated with the assembly of larger aircraft is rolling carts over small ramps used to protect anacondas, a nickname for bundles of cables and lines carrying power to the aircraft under construction. The ramps that protect the anacondas can be as high as 18 inches (46 cm). Moving carts up these ramps requires extra effort and going down ramps often is complicated by the need to apply brakes to slow down the cart as it descends the ramp.
Flight Attendants at Risk of Injury Pushing Service Carts
Pushing service carts down the aisles on commercial aircraft is also a task that can put operators at risk of injury. A report from Germany notes that flight attendants frequently reported discomfort from pushing service carts during short duration flights. The aircraft are often pitched up or down while the service is taking place, in effect requiring pushing the carts up and down slopes as high as 8 degrees 150 to 250 times per shift. The cart forces were evaluated using the ISO 11228-2 and CEN 1005-3 standards, which recommend force levels that 85 percent of all users can safely exert. The authors determined that the required forces often exceeded those recommended limits and concluded that steeper slopes sometimes increased the force demands to the point where only empty carts could be moved.
Clearly, this is an indication that the manual handling task needs to be optimized in order to keep flight attendants safe. The pitch of the aircraft on these short haul flights is unlikely to be changed and cart weight is also not a changeable consideration. But, there are other options to improve the safety of the task. The design of the cart itself should be the focus. By implementing ergonomic improvements to the cart, the force required to push it would be lowered; two areas to focus on should be handle placement and caster selection.
Airline Industry Should Focus on Ergonomics, During Manufacturing Process and Beyond
Wherever wheels move carts, tools such as the Liberty Mutual Tables or the ISO and CEN standards are useful in evaluating the safety of those individuals who make the wheels turn. Those involved in the design and manufacturing of carts used in the airline industry, whether in the manufacturing process or in-flight service, should focus on ergonomics to decrease the risk of injury in manual material handling tasks that serve to get the planes in the air.
Tom Albin PhD is a licensed professional engineer (PE) and a certified professional ergonomist (CPE). He holds a PhD from the Technical University of Delft in the Netherlands. He is a Fellow of the Human Factors and Ergonomics Society.
Tom has extensive experience as a researcher, corporate ergonomist, and product developer. In addition, he has been active in the US and International Standards community. He is accredited as a US expert to several International Standards Organization working groups and is Vice-Convenor of the ISO committee revising the standards for input devices and workstation layout/postures. He chaired the committee that revised and published the American National Standard ANSI/HFES 100-2007 Human Factors Engineering of Computer Workstations and currently co-chairs the committee working on a new revision of that standard.
