Mode S & ICAO 24 Bit Aircraft ID Questions

[Badmachine]

- How long (if at all) have US airline Boeing and Airbus planes been required to possess a 24 bit aircraft address for Mode S functions?

- How and where are these addresses set and contained? (the transponder unit, FMC, etc.)

- Although apparently forbidden, can such aircraft addresses be changed in mid-flight?

See:

EUROCONTROL - Mode S - Assignment of 24-bit aircraft addresses to State aircraft (http://www.eurocontrol.int/mil/public/standard_page/cns_sur_modes_24bAA.html)

Thanx! :ok:

[Graybeard]

The 24 bit address requirement goes back to the introduction of Mode S in 1987. Somewhere I have a Basic pgm that takes the N number and provides the 24 bit strapping, and vice versa. Other nations have their own numbering schemes, but the first digits represent the nation.

The aircraft i.d. in airplane types certified prior to about 1990 use 25 wires from each transponder to a shorting plug. Later planes have an aircraft i.d. module that transmits the i.d. to each transponder. Like ICAO says, they shall not be all ones or zeroes, and shall remain part of the aircraft registration.

TCAS will fault if the i.d. is all ones or zeroes. TCAS coordinates maneuvers with other TCAS equipped aircraft based on lowest number being in command.

GB

[Badmachine]

Thanks GB.

Would you know precisely how programming of the Aircraft Identification Module (AIM) is performed?

The earlier linked memo seemed to suggest that such AIM programming was technically possible during flight. Would this be done manually onboard via an interface terminal or remotely by a controlling authority?

It seems that remote access to such an important feature could have obvious safety or security implications.

[Graybeard]

I don't know about AIM programming, but it should be as solid as the tail number's paint. A tail number (registration) can legally have only one i.d.

Of course, I know certain SSR radar operators in southern Nevada area used to play games with airliners, such as having bogus targets approach from four different directions, causing the airliner's TCAS to go nuts. Once discovered, we had some USAF Reserve pilots get the word to them to knock that crap off...

GB

[Always Moving]

I am pretty sure that it can be change.
In the G-1000. MASTER OFF press and hold menu turn master on (now you are on maintenance mode) and you can change it.
I do not think is advisable but it can be done and am pretty sure it will be illegal I guess it is like painting the wrong tail number

[IceSpike]

No, the unique 24 bit code is issued by Airworthiness Authority then a tech converts to a Binary Code, setting is by strapping and or a locking thumbwheel at the Transponder depending on type.
The Mode S transponder sends the aircraft registration, you can easily change your RMUs, FMS, and other displays, but the transponder sends the code.
Can-not change it in flight.:=
Maybe why the manufacturers keep some components out of the driver's reach.

[Always Moving]

The one I am talking about is a HEXADECIMAL number if I remember correctly

[FlightPathOBN]

Why would you want to change this in flight? :suspect: