Traditional procedures supporting the next generation of aviation

As expanding regulations make it more and more routine to see small drones used by businesses, researchers and policymakers are looking ahead to the next frontier: when autonomous aircraft can carry not just small packages but large cargo, and uncrewed air taxis will be a normal feature of city skylines. 

That’s the vision captured under the terminological umbrellas of “Advanced Air Mobility” and “Urban Air Mobility.”

The Virginia Tech Mid-Atlantic Aviation Partnership, a Federal Aviation Administration-designated drone test site, has played a major role in bringing the safe integration of small drones to where it is today, where drones are delivering packages in neighborhoods around the country and major regulatory milestones such as safe operations over people are in the books. As complex as the work has been to get here, adding larger aircraft to the mix ratchets up the degree of difficulty. 

“When you’re talking about drones that weigh a few pounds, you’re looking at one level of risk,” said Tombo Jones, the test site’s director. “Aircraft that might weigh hundreds or thousands of pounds, that will fly the same types of missions as traditional crewed aircraft, dramatically expand the potential value of uncrewed systems, but they also introduce a much higher level of risk. Building on the foundational work we’ve done with small drones can help move us toward safe integration of larger aircraft. We’ll also borrow concepts and practices from traditional aviation, which already has very, very safe ways to deal with aircraft at that scale.” 

That’s the idea behind a recent collaboration between the test site, Virginia-based companies NAVOS Air and UAV Pro, and Textron Systems. The team considered how drones might take advantage of one of the foundational elements of modern airspace safety: instrument procedures. 

This collaboration resulted in the first known instrument approach design and flight test for an uncrewed aircraft system (UAS) in the country.

Instrument approaches to a landing facility are a set of predetermined maneuvers that take an aircraft gradually from its cruising altitude to a position where the pilot can safely land. Coordinating with air traffic control, pilots can follow these carefully choreographed flight paths navigating by instruments alone — crucial in any weather that reduces their visibility. Instrument procedures have been so successful at creating safe, verified flight paths that flights in cloudy weather are now totally routine and unremarkable. 

Their predictability also makes them a useful tool for managing traffic flow in the dense airspace around airports: An air traffic controller knows precisely where an aircraft on an instrument procedure will be.

“These procedures were designed to fly in weather, but they're heavily used to manage flow of traffic because the controllers and aircraft operators know exactly what’s going to happen when instrument procedures are utilized,” said Matt Burton of NAVOS Air. 

NASA’s newest “research roadmap” for developing the technological infrastructure that will be required to manage larger uncrewed aircraft identified a need for tools that can be used by air traffic control to keep these aircraft separated from each other and transition safely between higher and lower altitudes. Flying safely in inclement weather also has been flagged as an area to address. That raises the question of whether traditional instrument procedures could be used by — or adapted for — drones. 

“Advanced Air Mobility can benefit from these procedures the same way that conventional aviation does,” Burton said.

Instrument procedures are typically tailored for a particular type of aircraft and airport. In this case, the team focused on approach procedures at the Allen C. Perkinson Blackstone Army Airfield in Blackstone, Virginia, using a Textron Systems fixed-wing Aerosonde UAS. UAV Pro provided airport coordination and operations and safety management for the project flights. The research was funded by the Commonwealth of Virginia through a program designed to promote applied research in autonomous systems and commercialize existing research. 

The team began by assessing whether the Aerosonde UAS could theoretically follow the same instrument approach path that a helicopter would use at the Blackstone airport. An extensive analysis determined that the speed, climb rate, and other performance markers the Aerosonde UAS had demonstrated in previous flights indicated that it was capable of flying the helicopter approach. Flight tests verified the conclusions. 

“While flying an instrument approach is a new concept with a UAS, it is not much different to the way flight operations happen on a daily basis from the operator’s perspective.  The operator relies on flight instruments on a workstation computer similarly to that of a manned cockpit,” said Doug Shick, operation manager of Textron Systems, Air Systems Service and Support Center.

In fact, the team found, instrument approaches for drones can theoretically be more efficient and versatile than traditional ones. “We’ve learned that the approaches can be designed to take advantage of the capabilities of drones,” Jones said.

An instrument approach is typically designed to wind up with pilots in a position where they can safely use visual references to land. 

“That’s traditionally something like a 3-degree glide slope, so that they’re coming in nice and shallow as they transition from looking at the instruments out at the runway,” said Jones, a certified airplane and helicopter pilot himself. “They’re not turning or in some type of attitude that could be dangerous.”  

To work for conventional aircraft, those long, gradual approaches require clear swaths of airspace uncluttered by obstacles such as trees, tall buildings, or powerlines. That limits the environments where they’re feasible, and totally excludes, for example, urban centers crowded with tall buildings. 

But the risk of disorienting a human pilot isn’t an issue for a drone. 

“The drone doesn’t use visual references anyway. So the approach can actually be very different. It doesn’t have to be this long shallow descent,” Jones said. “The drone could fly right over the point it’s trying to descend to and do a spiraling turndown, for example, which would be extremely dangerous for a traditional pilot. A place that’s almost in a hole and would never be safe for a traditional pilot could be very safe for a drone.”

Condensing an instrument approach into a smaller volume of airspace means that they can be used in a broader range of environments, potentially including dense urban areas. It also will help decrease congestion in airspace that may need to accommodate more aircraft. 

“Part of the goal is to maximize airspace efficiency and safety,” Burton said. “If you tailor the flight procedure design to the aircraft performance profiles, they can be made to use a smaller volume of airspace.”

This project is one step toward integrating new types of aircraft smoothly alongside existing traffic by adapting strategies with a proven track record of ensuring airspace safety. 

Substantial research and extensive regulatory change lie between this moment in aviation and a future where helicopter-sized drones are ferrying human passengers around U.S. cities. Research that builds connections between new technology and traditional procedures may chart the course there. 

Aerosonde is a registered trademark of Textron Systems Corporation.