As you know,transport Ops'(In the USA) is covered by Code Federal Regulations Part121,foreign Carriers are covered by part 129,the specific operating items(T/down RVR,etc) are covered by"approved" Operational Specifications(ops specs').Generally approved by the FAA,based on the meeting the training 'legallities'of the home country,providing they meet FAA stndrds.So the T/dn requirement will be spelled out in each Carriers'Ops manual'and not read quite like the reg'(121) itself.