Lost Link
The loss of uplink severs command and control, requiring the system to execute pre-programmed logic in the absence of commands from the remote pilot.
Introduction to Lost Link
- Unmanned Aircraft Systems (UAS) are unique as they are operated through commands sent via line of sight, relayed by satellite relay, or by responding to pre-set programming in the on-board computer
- There are two components to lost link:
- Uplink that transmits command and control (C2) instructions to the aircraft, and;
- Downlink which relays the operation/status of onboard systems within the aircraft to the ground control station
- If either link is disabled or malfunctions, the result is defined as "lost link"
Lost Link Key Highlights
- Lost link situations occur when communication between a remotely piloted aircraft and the control station is interrupted or unavailable.
- Loss of command and control signals can result from interference, equipment malfunction, terrain obstruction, or excessive operating distance.
- Many unmanned aircraft systems are programmed with automatic lost link procedures such as hover, return-to-home, or autonomous landing functions.
- Remote pilots should understand aircraft-specific lost link behavior and emergency procedures before flight operations.
- Battery status, GPS availability, signal strength, and environmental conditions can affect lost link recovery capability.
- Proper preflight planning and operational risk assessment help reduce the likelihood of lost link events during UAS operations.
- Remote pilots should maintain visual line of sight and situational awareness to improve recovery options during communication failures.
- Operations near obstacles, urban environments, or radio interference sources can increase lost link risk.
- Improper lost link response can create hazards to people, property, and other aircraft operating within the National Airspace System.
- Understanding lost link procedures improves emergency preparedness, operational reliability, and overall aviation safety.
Lost Link Purpose
- The lost link algorithm provides a safe manner of operation and retrieval of the aircraft when operator control is lost
- This algorithm is intended to provide predictable system behavior
- In the event a lost link occurs, the system is designed to automatically control the aircraft in the safest manner whether on the ground or in flight for Lost Link
Lost Link Planning
- The available lost link procedure should, at a minimum, include lost link route of flight, lost link orbit points, lost link altitudes, communications procedures and pre-planned flight termination points if the event recovery of the UAS is deemed unfeasible
Transponder Operation
- Some aircraft transponders will automatically reset to code 7400, execute a pre-programmed flight profile and controllers will react accordingly
- Legacy systems may still Squawk Mode 3 7600, therefore ATC personnel will continue to treat each situation as a Lost Link and continue existing procedures
Air Traffic Control Procedures
- When you observe a Code 7400 display, do the following:
- Determine the lost link procedure, as outlined in the Special Airworthiness Certificate or Certificate of Waiver or Authorization (COA)
- Coordinate, as required, to allow UAS to execute the lost link procedure
- Advise Front Line Manager (FLM), when feasible, so the event can be documented
- If you observe or are informed by the PIC that the UAS is deviating from the programmed Lost Link procedure, or is encountering another anomaly, treat the situation in accordance with FAA J0 7110.65 Chapter 10, Section 1, Para 10-1-1(c)
Lost Link Knowledge Check
Lost Link Conclusion
- Unmanned aircraft can fall victim to emergencies, same as all other aircraft
- When that emergency situation involves an inability to communicate with an unmanned aircraft then UAS need to be programed with a plan to keep itself and others safe from a mishap
- Unmanned aircraft are only as smart as the logics they've been programmed with
- Operators must be proactive and maintain a current lost link plan
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