Verification of compliance and monitoring
As for all other aeronautical surveillance operators, the military can also provide a specific contribution to alleviate 1030/1090 MHz RF congestion. Such contribution must be organised taking into account all national prerogatives and responsibilities related with defence and security roles on the basis of processes and coordination mechanisms that safeguard in all circumstances sensitive information related with the military surveillance infrastructure.
It is up to the Member State to take adequate measures to discharge the responsibility to ensure that military fixed or mobile interrogators, for permanent or temporary operation, are correctly configured. Members States competent authorities¹ should implement the appropriate coordination processes and information repositories to ensure the assessment of the configuration of those interrogators. It is assumed that the Military authorities are aware of the criteria to be followed when assessing the surveillance sensor configuration. Military authorities should naturally confirm to their Member State authority that their fixed and mobile interrogators do not produce harmful RF interference on other aeronautical surveillance systems.
An RF Model can be used to show the compliance of surveillance systems with the requirements defined in the SPI IR Article 6. The RF Model can be tailored locally by a Member State. However, abnormal and unexpected events are not simulated. That is why this method is acceptable if the results are not close to the limits.
Real time 1090 MHz monitoring is out of scope of SPI IR but may be needed to detect the deterioration of the RF environment to enable a quick reaction. Unexpected increase in the number of transponder replies within a short period of time should be detected, reported and analysed. When such occurrences are identified, there must be a quick process in place to contact military operators if military surveillance infrastructure is involved. The socalled STOP buzzer procedure, already in place mostly for systems operated on non-interference basis under article 4.4 of the ITU Radio Regulations ie. Electronic Warfare training and exercises.
In case of a military exercise, military mobile interrogators may be temporary deployed and operated on Interrogator Identifier II=00. No Interrogator Code (IC) allocation is required for such mobile military interrogators, MLAT and WAM as these systems operate on II code 00. No IC allocation is required for Mode A/C radar neither. Therefore, no information will be maintained in the centralised code allocation repositories for these systems. This should be in line with Military authorities requirements to potentially conceal detailed information about the mode of operation of deployed interrogators.
Replies on II=0 represent one of the potential sources of 1030/1090 MHz RF pollution. The military is however not the root cause of this phenomena. Possible mitigation in this case include the removal of spurious replies (2020 long P4 removed) and optimization/tailoring of the interrogation pattern configuration of mobile platforms. Other sources of 1030/1090 MHz RF pollution, that are less-military specific, but that concern civil and military operators alike comprise:
- Mode S all call (acquisition) – to be mitigated through better configuration (e.g. reduced all-call interrogation frequency, probability of reply) of interrogators and passive/hybrid acquisition
- Long Mode S replies (EHS) – to be mitigated through reduction of extraction rate and sharing of data
- TCAS (local) - to be mitigated through use of Extended Hybrid Surveillance on new aircraft
Specific cases involving military interrogators