Australia: Ground testing by aircraft maintenance staff US: Non-discrete code assignments in accordance with FAA Order JO 7110.65, 5-2 US: Also for use in oceanic airspace, unless another code is assigned by ATC 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