Rules for Preventing Conflicts between Drones and Other Aircraft.

• Author: Holcombe, Randall G.
• Position: Essay

Drones, broadly defined, are unmanned aircraft that can be guided remotely or that can fly autonomously without direct human guidance. This definition encompasses a wide range of aircraft--and potential future aircraft--ranging from small remotely controlled aircraft flown by hobbyists to jumbo jets carrying cargo and perhaps passengers. Many readers are familiar with small drones flown by hobbyists. There are already more of them than there are registered aircraft in the United States. At the other end of the spectrum, although jumbo jets do not yet fly without pilots, their autopilots can be programmed to fly an entire flight without human intervention, from take-off to touchdown, so it is not difficult to imagine that in the future these aircraft will fly as drones, without pilots onboard. In the United States, the Federal Aviation Administration (FAA) certifies both aircraft and pilots and sets the rules under which aircraft operate. This paper discusses how those rules can be modified to incorporate drones into the air traffic system in a way that prevents conflicts between drones and manned aircraft as well as between drones.

The technology that enables unmanned aircraft is advancing rapidly, so any rules should be designed to accommodate not only present aircraft but also future uses. Many technology companies have already begun work to develop unmanned air taxis, for example, that will fly to a customer's location, pick him up, and fly him to a preprogrammed destination. Amazon has experimented with package-delivery drones that will fly purchases from a warehouse to a customer. Rules should be flexible enough that they can incorporate all types of unmanned aircraft. To understand how rules can be established to integrate drones into the air traffic system requires an understanding of both the technology and the rules under which aircraft fly and how the technology and rules can prevent conflict.

The technology is available today, although one can imagine future technologies that might be better suited for drone flight. The rules require some type of modification to accommodate drones and perhaps should be completely overhauled not only to accommodate drones but also to make the air traffic control (ATC) system more efficient for all aircraft. After a brief discussion of the technology, this paper focuses mainly on the rules. The simplest possible rule change, one that would work with today's technology, would be to mandate that drones have the responsibility for avoiding all other aircraft, including other drones. Consistent with present rules, the adopted rules might require the FAA to certify the collision-avoidance technology of drones before allowing them to fly, if only to standardize how aircraft can communicate their positions and collision-avoidance strategies to each other.

This paper concludes that a redesign of the rules to accommodate drones can lead to a redesign of the rules for all aircraft, thus increasing the efficiency and utility of the ATC system for both manned and unmanned aircraft.

The Technology of Aviation-Collision Avoidance

The most basic system of collision avoidance, established early on and still in use today, is to have pilots look outside their aircraft to see and avoid other aircraft. Aircraft using that method today are required to stay clear of clouds and fly in visibility good enough to be able to see other aircraft. When weather conditions preclude this, or if aircraft operators choose to fly on a flight plan even in good weather, aircraft fly under flight plans and follow the directions of air traffic controllers, who are responsible for preventing collisions.

The present rules for ATC were developed in the 1940s and have changed little since then. Although the rules were designed for the technology available in the 1940s, the technology for collision avoidance has advanced considerably. The present rules were designed in an era when few locations had radar services, so pilots would track their own locations, aided by ground-based radio navigation facilities, and report their positions via radio to controllers. Controllers would keep track of those locations and would issue instructions to keep aircraft separated from each other. As the use of radar became more widespread, air traffic controllers could see aircraft as blips on their radar screens so that, combined with pilots reporting of their locations, controllers could identify specific blips with specific aircraft. Separation of aircraft was and still is undertaken by air traffic controllers, who keep track of the locations of aircraft. Three significant advances have enhanced the technology of collision avoidance.

First, each aircraft is required to be equipped with a transponder that transmits its location, including altitude, to air traffic controllers. (1) Transponders aid air traffic controllers in identifying aircraft and directing them to avoid conflicts. The transponder allows air traffic controllers to better manage traffic conflicts but does not provide any information or direct assistance to pilots. Transponders are one-way communication devices that send information from aircraft to air traffic controllers.

Second, the Traffic Collision Avoidance System (TCAS) became required equipment on all airliners and was made available for other aircraft. TCAS provides an in-cockpit display of the transponder returns of other nearby aircraft. Coupled with transponder technology, TCAS allows aircraft to electronically see and avoid other aircraft. TCAS-equipped aircraft do not need to visually see other aircraft to detect potential conflicts and steer away from them because TCAS electronically displays them.

Third, Automatic Dependent Surveillance-Broadcast (ADS-B) is available now and will be required equipment on most aircraft beginning in 2020. Similar in principle to TCAS but using different technology, ADS-B uses a global positioning system (GPS) so aircraft can determine and broadcast their own positions. Other ADS-B-equipped aircraft then receive the locations of nearby aircraft, which are displayed in the cockpit. Like TCAS, ADS-B allows aircraft to electronically see nearby aircraft regardless of whether those aircraft can be seen visually, allowing aircraft to steer away from potential traffic conflicts. ADS-B does not require any action on the part of air traffic controllers. Aircraft broadcast their ADS-B data, and other aircraft receive those data directly. Air traffic controllers also receive the data, which help them separate aircraft, but one big difference between ADS-B and the earlier transponder technology is that ADS-B shares data among aircraft directly so they can electronically see each other without involvement by air traffic controllers, whereas transponder data are sent only to controllers, not to other aircraft. (2)

This is a brief summary of the currently available technology for air traffic conflict avoidance. The key point is that the technology already exists for aircraft to electronically locate nearby aircraft so that they can avoid collisions, without the guidance or intervention of air traffic controllers. (3) The following analysis takes this technology for granted to focus on the rules for avoiding conflicts between drones and other aircraft.

Two Types of Flight Rules

The current ATC system allows aircraft to fly under two sets of flight rules. Some flights operate under one set of rules, whereas others operate under the other set. Under visual flight rules (VFR), aircraft fly where they want, when they want, and are responsible for seeing and avoiding other aircraft. No flight plan is required under VFR, and although pilots can file a flight plan, they are not required to follow it. Exceptions are that at altitudes higher than 18,000 feet or when in the vicinity of an airport with a control tower, pilots must follow the instructions of air traffic controllers. (4) Under instrument flight rules (IFR), aircraft are required to file a flight plan, which then must be approved by and may be...