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"

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 Procedure:

  • 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)


  • 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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