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  • Travis Paul and Nate Murphy

Autonomous aircraft: Why C2 links matter



Xwing monitoring an autonomous flight from a Mission Control Center during an Air Force exercise. Photo credit: Matthew Clouse, AFRL
Xwing monitoring an autonomous flight from a Mission Control Center during an Air Force exercise. Photo credit: Matthew Clouse, AFRL

Xwing recently demonstrated the flexibility of Superpilot™️ our autonomous flight system, as part of the Air Force’s AGILE FLAG exercise. Xwing’s approach to autonomy is a direct path toward uncrewed operations, meaning that the aircraft flies itself, handles failures and contingencies automatically, and safely completes its missions with human supervision from a ground control station. Though the plane does not need a human to operate or complete a mission, the Command and Control (C2) links provide significant operational flexibility and important data and context from the human operator. As Xwing continues to develop this dual-use technology, multiple links within our Communications Management System (CMS) will be part of our FAA certification of our Uncrewed Aircraft System (UAS) for commercial operations.


If you are not involved in aviation, you may not know everything a pilot does to get you safely to your destination. A pilot has significantly more responsibilities than simply flying the aircraft. With advanced autopilots, the act of flying has become more automated. The challenge is to solve all pilot responsibilities, not just the flying. It is crucial to address all these responsibilities comprehensively when designing a system that will not include a pilot from the cockpit.


What does a pilot do?

The pilot is responsible for far more than safely flying and landing for each flight they command. A pilot’s job starts well before the flight, from reading flight plans and weather reports to ensuring that all cargo and passengers are safely loaded. Before takeoff, the pilot ensures that the plane is flight-ready with a pre-flight inspection. They then communicate with Air Traffic Control (ATC) instructions for taxiing and obtaining takeoff clearance.


Once in the air, the pilot can manually fly the plane or engage an autopilot. Throughout the flight, the pilot is responsible for talking with ATC and adjusting the flight plan if needed. If something goes wrong, the pilot will execute emergency procedures with or without the assistance of automated systems. Upon approach, the pilot will talk with other pilots and ATC to coordinate the landing and receive taxi and gate instructions. Once stopped, the pilot will shut down the engines, check that everything is operating normally, and log the flight.


What does a remote supervisor do?

Xwing’s Superpilot is a “human-on-the-loop” system. This means that the uncrewed aircraft can independently taxi, takeoff, land, and respond to dynamic flight conditions. However, a remote supervisor, located in a Mission Control Center (MCC), monitors the flight. The supervisor communicates with ATC, ground crews, and other aircraft on behalf of the uncrewed aircraft and provides instructions as needed to the uncrewed aircraft in flight.


Xwing’s system is not designed for remotely piloted aircraft (RPA) as the remote supervisor cannot directly manipulate the flight controls, i.e., they do not have stick and rudder controls. The onboard autonomy system provides all the capabilities of a conventional autopilot, for example, stabilization, trajectory following, and engine management. Additionally, it introduces new capabilities like hazard avoidance, mission replanning, emergency response, and other functions necessary to get the plane safely from point A to point B.

Xwing's Superpilot Makes any aircraft self-reliant through all stages of flight.
Xwing's Superpilot Makes any aircraft self-reliant through all stages of flight.

To do this, the MCC communicates with the uncrewed aircraft via a digital data link for Command and Control. Our system uses several types of data links but primarily air-to-ground and satellite communications (SATCOM) links.


SATCOM links are particularly useful for long-range Beyond Visual Line of Sight (BVLOS) operation. When used in conjunction with perception systems and vision-based sensors, SATCOM enables the aircraft to operate autonomously in previously unsurveyed and operationally limited or austere environments. The capability to land autonomously in never-before-visited locations is critical to mission effectiveness in an Agile Combat Employment (ACE) operational concept.


SATCOM-enabled autonomous flight in action

Xwing participated in the Air Force’s AGILE FLAG 24-1. The Total Force exercise, which ran from January 22 - February 4, 2024, brought together Air Combat Command (ACC) and Air Mobility Command (AMC) at military bases and public airports throughout California centered on Agile Combat Employment. 


“Agile Combat Employment is built on the idea of small teams of Airmen dispersing to operate from numerous remote or austere locations. In the Pacific, those locations will likely be many small islands with limited resources. Moving teams around and ensuring they get the equipment they need is a massive logistical problem that Air Mobility Command has been working on.”


With agile basing and dispersed logistics in contested environments, you can’t assume that ground infrastructure will be available as it may not be built or compromised. In addition, missions may require an autonomous aircraft to assess and reroute to new locations without prior experience.


Left: Xwing mobile ground control station ready for demonstrations at Sacramento McClellan Airport; Right: Xwing’s autonomous flight routes to military and public airports for the AGILE FLAG 24-1 exercise.
Left: Xwing mobile ground control station ready for demonstrations at Sacramento McClellan Airport; Right: Xwing’s autonomous flight routes to military and public airports for the AGILE FLAG 24-1 exercise.

During AGILE FLAG 24-1, the remote supervisor remained at McClellan Sacramento Airport in Xwing’s mobile MCC. Throughout the week-long exercise, Xwing transported mission-critical cargo with daily autonomous missions, accumulating over 2,800 autonomous flight miles to 8 different military bases and civilian airports, including March Air Reserve Base, Vandenberg Space Force Base, Sacramento McClellan Airport, Meadows Field Airport, and Fresno Yosemite International Airport. The exercise took place across Northern and Southern California, requiring Xwing to integrate with several other aircraft in both public and military airspace. 


To ensure we could effectively integrate in shared airspace, we employed a multi-network approach using a combination of air-to-ground and SATCOM datalinks. Air-to-ground datalinks provided high throughput, low latency, and reliable connection in areas with available ground infrastructure. SATCOM provided a flexible coverage area, supplementing when air-to-ground coverage was limited. For SATCOM, we partnered with Viasat.


Xwing conducted extensive testing using Viasat’s L-band network for BVLOS autonomous flight. In the past year, we sent a significant quantity of data over Viasat’s network to support a variety of network performance tests, autonomous flight tests, and demonstrations.


The AGILE FLAG autonomous flight missions were on-demand and required Xwing to land and navigate to and from new locations. We had previously landed at only two of the eight airports before. This exercise demonstrated the global coverage advantage of SATCOM to meet ACE mobility requirements.


How do redundant C2 links improve operational flexibility?

Chart showing flexible tasking with and without C2 links

To ensure mission success, Xwing uses a mix of diverse networks/datalinks to ensure adequate C2 reliability. We used RTCA DO-377 as a standard for defining functional requirements and required C2 link performance. The Communications Management System (CMS) operates across these diverse networks to create redundant data paths and expand the operational area for increased flexibility. We partner with best-in-class communications service providers like Viasat to establish local service level agreements to meet C2 coverage, reliability, and throughput requirements.


Redundancy and reliability

The CMS handles data routing across networks as needed, monitors data link status, and ensures the integrity of the data transport using authenticated encryption algorithms. Xwing coordinates with communications service providers to ensure spectrum and network resources are available for the uncrewed aircraft’s planned route.


The CMS will also handle C2 responsibility transfer from one remote supervisor to another. The transfer could be between two supervisors within the same MCC or between supervisors at dispersed locations.


Seamless communications

The C2 data links are used to relay voice communications from the remote supervisor to ATC. Xwing integrates seamlessly into the National Airspace System (NAS) and will meet VHF communication requirements. The CMS relays digital voice from the remote supervisor into an analog voice for VHF transmission to ATC and other aircraft, performing the reverse conversion as well.


Lost link management

In the case of a network outage, equipment failure, or extended interruption, the uncrewed aircraft may declare a Lost C2 Link state. MCC monitoring will also notify the remote supervisor. In this case, the uncrewed aircraft will autonomously continue to navigate per its Lost C2 Link state plan, which may be to continue on the planned path or divert to a secondary location. If required in a Lost C2 Link state, the remote supervisor can contact ATC through alternate means.


Austere and remote locations

Line of sight (LOS) data links require supporting ground infrastructure like antennas or network backhaul to provide adequate coverage. This requirement can be challenging in austere environments or low-altitude operations with significant terrain. LOS data links can provide reliable low-latency links for predetermined routes, congested airspace, or around primary airports.


The addition of SATCOM provides link diversity to complement LOS links to increase reliability in case of network failures or temporary interruptions. Aircraft maneuvering or terrain blockage could cause a temporary interruption in one data link while the other remains active. SATCOM can provide significantly better coverage areas than LOS links but can come with increased latency and operational costs.


The recent Xwing demonstration of autonomous flight capabilities underscores the critical importance of Command and Control (C2) links in enhancing operational flexibility and ensuring mission success. While the Xwing autonomous aircraft are self-sufficient, redundant and consistent C2 links provide essential data and context from human operators, enabling effective supervision and communication throughout missions. The utilization of diverse networks and emphasis on robust C2 links enhance operational flexibility and contribute to the safe and efficient integration of autonomous aircraft into both military and commercial airspace. As we continue to advance our autonomous flight technology, the optimization of C2 links will remain a cornerstone of our efforts to deliver reliable and adaptable autonomous technology to support diverse mission requirements.

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