It seems ICAO 24-bit Aircraft Addresses duplication may be a practical ATC problem in Europe. Major Donald L. McCallie (USAF) says in
:
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ada545599
http://www.dtic.mil/dtic/tr/fulltext/u2/a545599.pdf
6.2.4 Impact of duplicate 24 bit ICAO addresses
To increase security, DoD and government aircraft transponders are not required to have fixed 24 bit ICAO addresses. This exception to policy has introduced human error into the ADS-B technology. It has been noted in European airspace, where ADS-B is already being used that U.S. military aircraft are routinely flying with duplicate 24 bit ICAO codes.
As the FAA brings ADS-B and NextGen upgrades online in the U.S. it is likely that we will see these same conflicts occur here. Research in this area should explore how FAA controllers and the NextGen system will handle duplicate codes and if this exception could be used by an attacker to further exploit the system.
An interesting document on NATO practice of continually changing the ICAO 24-bit Aircraft Address says:
https://www.eurocontrol.int/articles...eld-tabs-tab-1
Military Use of 24-bit aircraft addresses
In NATO member States, authorities have apportioned part of their overall available 24-bit aircraft addresses for military use. The relatively large number of aircraft addresses for military use allows rotating the assignments of 24-bit addresses on military aircraft on a frequent basis. The purpose of this random changing of addresses is to conceal information on military airframes allowing building up an Air Order of Battle. A controlled rotation of 24-bit addresses is therefore not considered to be in contradiction with the above principles. This rotation of 24-bit addresses however must not be done during flight.
When using the Mode S transponder in flight, unique and correctly assigned aircraft addresses must be used. The occurrence of duplicate 24-bit addresses can jeopardise the safety of aircraft and the operational efficiency of ATM functions and therefore must be avoided at all times.
SSR Mode S Interrogators & Radar trackers: The uniqueness of the 24-bit aircraft address is important for the unambiguous identification of the aircraft. Effects of duplicate addresses are unpredictable. This can cause synchronous garbling, radar track swapping or dropping.
- ACAS II: ACAS II systems use Mode S protocols and transponders to maintain safe separation between aircraft. Duplicate 24-bit addresses can have serious safety implications, i.e. one or more of the ‘threat’ aircraft can remain partially or totally undetected.
Note an interesting sentence that adds to the EASA document:
This can cause synchronous garbling, radar track swapping or dropping
Unfortunately it seems that this subject was exploited by conspiracy theorists and these types discredit everything they touch.