Canada: VFR flight above 12,500' ASL when no other code has been assigned Japan: VFR flight above 10,000' MSL when no other code has been assigned US: External ARTCC subsets (Discrete codes of blocks only except for first primary block, which is used as the ARTCC's non-discrete code if all discrete codes are assigned) UK: NATO – CAOC Uedem (activated by NOTAM via ASACS Force Command)
SBO