Lost-Links and Mid-Air Collisions: The Problems With Domestic Drones

[The Straight Story]

Most of the public discussion surrounding the use of drones both internationally and domestically has focused on issues of privacy or civilian casualties. Due to the technical complexity of drone operations, there has been little media examination of the practical feasibility of widespread domestic drone deployment. In February, the FAA Reauthorization Act of 2012 was signed into law clearing the way for more than 30,000 domestic drones by 2020. The law requires the FAA to create procedures for commercially-operated drones by 2015 and enables law enforcement agencies to operate small-scale drones at low altitudes. While this has a number of negative implications for the right to privacy, such as the lack of any laws governing the usage of data collected via drones, the thought of a future where U.S. skies are filled with an array of drones has a much larger, more practical problem: is it even logistically possible to operate thousands of pilot-less aircraft in the domestic airspace?
Lost-Links

The first set of problems that will likely plague any attempt at the widespread use of drones inside the U.S. relate to frequency allocation and electromagnetic interference (EMI). In order to be controlled from a remote location, drones must communicate via with a ground control station via some sort of data link. In order for this link to be maintained, there must be protection against electromagnetic interference that can disrupt the communications link. If the interference is sufficient in scale, it can lead to what is called a lost link event causing the drone to lose contact with its operator. Sometimes the link is reestablished and the pilot is able to maintain control of the drone. Sometimes the link cannot be reestablished and the drone is effectively turned into a zombie that can drift far from its intended target, as may have occurred recently with the RQ-170 captured by Iran in December 2011.

A U.S. Air Force Scientific Advisory Board report from April 2011 obtained by Public Intelligence warns of the potential vulnerabilities of communications links used for remotely piloted aircraft (RPAs): “Limited communications systems result in communications latency, link vulnerabilities, and lost-link events, which limits mission roles assigned to RPAs, operational flexibility, and resiliency in the face of unanticipated events.” The report notes that there are a “wide range of methods that a determined adversary can use for attacking RPA guidance and navigation systems” such as constructing “simple GPS noise jammers” that “can be easily constructed and employed by an unsophisticated adversary.”

...

In fact, mid-air collisions have occurred in the course of combat operations. In May 2011, a RQ-7B Shadow and a C-130 cargo plane collided over Afghanistan. Though no one was injured, the C-130 was forced to make an emergency landing. In response to the incident, a FAA spokesperson told AOL Defense that there are several studies indicating that “you could not use TCAS to reliably have other aircraft detect the unmanned aircraft.”

TCAS or the Traffic Collision Avoidance System is the standard technology used by commercial aircraft around the world to help avoid mid-air collisions. The system, based on transponders that operate in each aircraft independent of air traffic control, reportedly has difficulties incorporating drones due to their lack of a pilot and often unpredictable flight patterns. A U.S. Air Force study conducted by MIT states that TCAS was “designed under the assumption that a pilot was on-board the aircraft to interpret displays and perform visual acquisition. The TCAS traffic display is intended to aid visual acquisition by indicating the proper sector to search out the cockpit, but does not by itself provide sufficient bearing or altitude rate accuracy to support avoidance maneuvers. The role of a TCAS traffic display in a UAV ground control station is therefore under debate.”

http://publicintelligence.net/the-problems-with-domestic-drones/

[Ian David]

1. Shut-up. You're going to kill my future business of delivering pizza by helicopter drones. n/t

[ProgressiveProfessor]

2. ADS-B, the successor to TCAS will help in the national airspace, though its use is not mandated

Yet. The issue will be in Class E or other lower use airspace where there is no intention to mandate it at his time.

[tech3149]

3. I fly RC airplanes and have been in electronics all my working life

Loss of link while still possible would not be a major point of concern. Mid air is a much greater problem and most likely to affect private pilots.

As far as the lost link problem, what is currently used for modeling is a good indication of what is possible even though we are probably a decade behind what is available.
Most current radios are working on the 2.4Ghz band where power output is limited. All of the radio systems use what is called a GUID (globally unique identifier). This requires the receiver to be bound to the transmitter and only respond to that transmitter. They also use some form of spread spectrum or channel hopping to avoid interference with other users on the band. Other features like fail safe mode, multi axis gyro stabilization, and accelerometers can aid in avoiding loss of control damage.
I don't post this as a defense of drone usage but but to point out that technology is already available to minimize the danger of their usage.