Squawk code · special

Squawk 1000: IFR Mode S conspicuity (Europe)

Squawk 1000 is a conspicuity code used in Europe for IFR flights that ATC identifies by Mode S address instead of a discrete code.

Squawk 1000 is a code used mainly in Europe for IFR flights that controllers identify by their Mode S address instead of a unique squawk. It helps save scarce codes in busy airspace.

What 1000 means

There are only 4,096 possible squawk codes (0000 to 7777 in octal). In crowded European airspace, controllers can run out. Mode S transponders broadcast a unique 24-bit aircraft address and the flight's callsign, so radar systems can identify a flight without a unique code. Where this "Mode S conspicuity" procedure is in force, controllers assign 1000 and track the flight by its Mode S data instead.

Is 1000 used in the US?

US controllers continue to assign discrete codes to IFR flights, so 1000 is not a routine code here. The FAA distributes codes to facilities through its own national beacon code allocation plan, which does not use 1000 as a conspicuity code. If you see 1000 in our US snapshot, it is most likely a transatlantic flight that has not yet been reassigned, an aircraft near the edge of coverage, or a data quirk.

How 1000 appears on heywhatsflying

Nothing special happens with 1000: the aircraft shows normally. Its hex address and callsign are what identify it, as explained in callsigns, registrations and hex codes.

Why codes run short

Four octal digits give exactly 4,096 combinations. A discrete code assigned to one flight has to stay unique across every radar sector that might see it, and a busy area may have thousands of flights in the air. Some codes are also permanently reserved, such as 7500, 7600 and 7700. Mode S identification lets the same non-discrete code, 1000, be shared by many aircraft at once, because the radar system tells them apart by their 24-bit addresses.

Related codes: 7000 (European VFR) and 2000. See the squawk code index.

Questions

What does squawk 1000 mean?

In Europe it marks an IFR flight that controllers identify by its Mode S address rather than a unique squawk code. It helps conserve the limited supply of 4,096 codes.

Do US flights use squawk 1000?

Not routinely. US controllers still assign discrete codes, so 1000 in US data usually comes from an international flight or a data quirk.