Lost Link
Unmanned aircraft operations must account for the possibility of communication interruptions between the pilot and the aircraft. Understanding lost link procedures in remotely piloted aircraft operations helps operators recognize how preprogrammed responses and contingency planning support safe recovery and airspace protection.
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 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 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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