Hex Codes and their allocation

[Rerun57]

Is there a centrally coordinated allocation of hex codes for transponders? Do the same hex codes remain with each airframe "in perpetuity"? Is there a published source of any such allocations? Very new to this and absolutely fascinated! Any pointers/replies would be most gratefully received.

Many thanks in anticipation,

Adrian James

[DaveReid]

Is there a centrally coordinated allocation of hex codes for transponders?

No.  The blocks of codes allocated to each country are defined by ICAO, but it's up to each country how these are allocated to individual airframes.

Do the same hex codes remain with each airframe "in perpetuity"?

Not necessarily.  The only reasonably reliable rule is that while an aircraft retains the same registration, the hex code shouldn't change.  If it is re-registered in the same country, then the code may of may not change according to how the country does the assignment (e.g. a UK code won't change with a change of G- registration, a US one will with a change of N-number, etc).  Only when an aircraft moves from one country's register to another is it strictly necessary for the code to change (since each country has a different allocated block).

Is there a published source of any such allocations?

Quite a few countries publish individual aircraft allocations, but there is no official worldwide published hex code register (although several commercial organisations collate known codes and make them available to their clients).

[Rerun57]

Many thanks for the reply. I have noticed (for example) that the US Military codes that I have received over the last few days all start with a limited range of characters, likewise for the UK Military codes. This would seem to be intentional then?

Thanks

Adrian

[Allocator]

Many thanks for the reply. I have noticed (for example) that the US Military codes that I have received over the last few days all start with a limited range of characters, likewise for the UK Military codes. This would seem to be intentional then?

Thanks

Adrian

There has been a fair amount of detective work with these Hex code allocations in the past, based on what people have picked up.  There is a long thread on the Kinetic forum discussing this - some 30 pages - but it might help you to understand the situation if you read through this:

http://www.kinetic-avionics.co.uk/forums/viewtopic.php?t=4023&postdays=0&postorder=asc&highlight=countries+dat&start=0

[DaveReid]

Many thanks for the reply. I have noticed (for example) that the US Military codes that I have received over the last few days all start with a limited range of characters, likewise for the UK Military codes. This would seem to be intentional then?

The US system is relatively straightforward.

Civil Mode S codes are allocated in the range A00001 (N1) to ADF7C7 (N99999).  That accounts for 915,399 codes out of the USA's allocation of 1,048,576 codes (A00000 isn't used), and the remaining ones from ADF7C8 onwards are available for use by the military.

The UK's system is broadly similar, except that codes aren't pre-allocated to registrations.  The allocation is 400000 to 43FFFF, with civil codes starting at 400400 and the highest allocated code so far being 406179.  Military codes start at around 43C000, and around 3,000 or so have been allocated.  Beyond the military block is a relatively recent allocation for the Isle of Man with (I believe) a range of 500 codes in the 43Exxx range.  The thousand or so codes in the range 400000 to 4003FF are mostly reserved for Bermuda and the Cayman Islands, other than a few test/military codes at the very beginning of the sequence.

HTH, any other questions please ask.

[Rerun57]

Dave, another helpful reply. I have been using the Hex codes as a way of trapping (by alarm) military flights, and it has seemed pretty reliable since I started all this a few days ago. Many thanks, Adrian

[ACW367]

The Manchester TMA spotters have a useful table of country allocations.  Although I am not sure which official sources (or otherwise) they drew the information from

http://www.mantma.co.uk/icao%20allocations.html

http://www.mantma.co.uk