Air Defense Identification Zone (ADIZ)
In several regions an ADIZ is established. In some of them, pilots have to call ATC before crossing the ADIZ boundary to request an ADIZ clearance (e.g. Karachi FIR). The respective zones (countries) are indicated on the Route Facility Chart (RFC). An air defense clearance number (ADC-number) will be issued from the responsible air defense unit. This number should be reported upon request by the ATC unit concerned.
In several regions an ADIZ is established. In some of them, pilots have to call ATC before crossing the ADIZ boundary to request an ADIZ clearance (e.g. Karachi FIR). The respective zones (countries) are indicated on the Route Facility Chart (RFC). An air defense clearance number (ADC-number) will be issued from the responsible air defense unit. This number should be reported upon request by the ATC unit concerned.
Source: EU-OPS