On May 7th this year, air traffic aficionados (and controllers) in the United Kingdom will have to add another conspicuity code to their memory bank. Squawk code 7400 is to be used exclusively by unmanned aircraft that have lost communications with their remote pilot, and have reverted to autonomously flying a pre-programmed route.
Why code 7400 is needed
So, why not just use any of the already existing codes? Couldn’t 7600 (radio failure) or 7700 (general emergency) be applied and work just as well? Apparently the UK CAA feels otherwise, and after gently masseusing our think tanks, we are bound to agree.
Let’s start with perhaps the most famous of the conspicuity codes—the almighty 7700. When used, an aircraft immediately will soar to the top flight of aircraft currently tracked on Flightradar24. It basically means that the aircraft is experiencing an emergency, the extent of which may put human life at risk. Should an unmanned aircraft happily flying along a pre-programmed route after having lost comms with its operator fall under this category? No, probably not.
But what about 7600? Isn’t the above scenario the very definition of a communications failure?
Well, squawking 7600 would imply that there is at least one pilot who can still see and control the aircraft but that all means of voice and data communications are lost. In the case of a remotely controlled aircraft, this isn’t exactly the case. At this point, there is no human involved, the drone is on its own. A dedicated code hence is a clever way to let controllers immediately know what he or she is dealing with. In this case, an unmanned aircraft and that it is following a pre-determined route to a presumably safe location.
When is 7400 used?
The new rules apply to UAS (Unmanned Aerial Systems) operating “beyond visual line of sight” (shortened BVLOS). Typically, a drone operating in controlled airspace would have informed the local air traffic service about its intentions and what kind of procedure to fly if connection is lost, before getting airborne.
If 7400 appears on the screen, the flight controllers then would know to cross-reference that pre-briefed procedure and protect the airspace accordingly. If the actual routing flown would differ substantially, it would be treated like any unknown aircraft.
Not adopted worldwide
The UK is not starting from scratch here. The United States FAA in fact authorized the use of 7400 already in 2016. For US-operated UAS flying under FAA jurisdiction, 7400 has therefore been the expected lost-link squawk for nearly a decade.
It’s noteworthy that the code hasn’t been officially recognized by the ICAO yet. Europe’s EASA updated its Standardised European Rules of the Air (SERA) in 2025 and introduced a new code (7601). That covers radio communication failure in crewed aircraft, but so far anything similar for drones losing contact with its master has failed to materialize.
As it isn’t globally recognized yet, you will not see UAS squawking 7400 on Flightradar24 at this time. But who knows what the future holds?
2 Responses
If the controller/pilot has lost contact with the drone how can he change the transponder code, or is it programmed into the drones flight controller to change the code automatically if comms are lost ?
It is an automated process.