A version of this article appears in the September 8 issue of Aviation Week & Space Technology.
The FAA approved the first unmanned aircraft flights over land in June. While limited in scope to aerial surveys of Alaska’s North Slope, these flights nonetheless are a step toward broader use of these vehicles in the national airspace system. As the industry moves in this direction, it is important to note that operation of unmanned aircraft systems (UAS)—and in particular, small unmanned aircraft (UA) weighing less than 100 lb.—introduces some unique maintenance-related human factors issues.
Alan Hobbs of San Jose State University presented many of those issues to the ICAO UAS Study Group on June 30. Hobbs, working with -NASA’s Ames Research Center, has spent much of the last decade researching human factors in the maintenance of unmanned aircraft. His findings are presented in a 2008 FAA report, “Maintenance Challenges of Small Unmanned Aircraft Systems—A Human Factors Perspective.” Hobbs calls attention to several issues:
Extensive knowledge requirements. The most significant difference between maintenance of conventional aircraft and UAS is that the UAS technician is responsible for the entire system. In addition to the engine, airframe and avionics, technicians must maintain a diverse array of ground-based equipment and the links between all the systems.
Given the potential risk of electromagnetic interference (EMI), Hobbs says technicians also should understand radio transmission, wireless communication and antenna electronics. And with guidance and control of most small UAS conducted on standard laptop or desktop computers, this equipment becomes an airworthiness concern—and potentially falls within the purview of the maintenance technician. With so much to know, there is increased potential for error.
Lack of pilot input. In manned aircraft, the pilot is a layer of defense against maintenance problems. Not only do their logbook entries identify issues, their pre-flight checks can catch safety mistakes. In unmanned systems, this layer of defense is removed. While flight history and system status reports are available, they do not contain information about a pilot’s direct sensory experience of the aircraft’s flight performance.
Complacency. This issue is of particular concern in UAS maintenance. The reason: “There is the potential for technicians to be of the mindset that their work is less critical because there isn’t a human being transported on the system,” warns Hobbs.
Remote-control culture. In a 2005 study co-authored with Stanley Herwitz, director of the UAV Collaborative Center at NASA Research Park, Hobbs found the most commonly cited skill sought for UAV maintenance personnel was experience with remote-control aircraft. However, such personnel do not necessarily have a mainstream aviation background. “Remote-control hobbyists may be accustomed to operating without formal procedures or checklists,” he observes, “and may be unfamiliar with the ethics and standard practices of aircraft maintenance, and the legislative framework within which maintenance occurs.”
To get ahead of these issues, Hobbs urges the industry to identify the things that haven’t yet had a negative consequence but could—and take them seriously. “Something that hasn’t been done enough in maintenance is to identify tasks where we are working without safety nets—without a backup or barrier or defense against a mistake,” says Hobbs. “There are surprising situations where you’d think there would be a check but it is not present. In the maintenance of unmanned systems, we need to ID the areas where we are one mistake from an accident. We need to do all we can to produce systems that are robust and can tolerate an error.”
This is critical, as UA operations shift the balance of risk in ways that must be understood by maintenance personnel. In conventional aircraft, safety risks are borne primarily by those who actively accept the risks and benefit from the flight (i.e., flight crew and passengers). In unmanned flight, the risks are borne by others who did not agree to be exposed to that risk—people on the ground and in other aircraft. Hobbs says this changes the standard we have to apply in managing that risk. “The fact that no one is on board means we have to take even greater precautions to protect the people who didn’t sign up for the risk.”
The most pressing issue may be lack of historical data and perspective. “We don’t have 70 to 80 years of experience behind us, as manned flight does. We are still in a learning period. The issues that ultimately emerge,” Hobbs concludes, “may be different than what we think they are today.”