I think the legal ICAO requirement is 1 dot high, zero low (sustained).
Thanks for your replys. Looks like the legaltys are spelt out black and white as far as the FAA is concerned but still a bit up in the air as far as ICAO goes. Its quite possible this one-dot low business may vary in the legal sense acording to the A.I.P. of each individual Contracting State.
Your dead right K.M.! You only need to acidentley bang the wingtip into a parked dunny truck, and the Inquisition cardinals and bishops will go right through everything including your prev rest period duration, what you had for breakfast, the CVR, FDR, checklist/briefing thoroughness etc etc etc, even if its entireley unrelated to the incident. If a one-dot low approach was discovered you can bet theyll search everywhere to see if they can hang that on you too!
RAT 5 as far as I know (and dont ask me who made THIS one up!) its only legal for RPT abv 5700 kg to continue, or commence, a non-guidance approach as long as the last guidance system fell over AFTER your arrival within 5nm of the ARP ( be it DME, or ILS G/S, LLZ marker-beacs, or VASIS). If it happens BEFORE you get there a D.C.A. dispensation is required to conduct a no-slope aproach. A good example is a pure NDB let-down for a straight-in, where the VASIS suddenley went bung during your inbound turn and your MORE than 5nm from the ARP. If another runway with a servicable vasis is available, then get to the cclg min and use it. If because of wx, wind, notams, terrain etc you cant, then to continue inbound and land off a no-slope aproach requires authorisation. In most cases ATC (the SATCO on duty or 'STAC' as hes known) has the power to act on behalf that countrys D.C.A. If the failure occurs WITHIN 5nm no authority is required and its up to the PIC to determine if he wants to continue and land (and considering also what the Company lays down, if any, regarding such an exercise).
I dont know any case anywhere where ATC has refused any aircraft a no-sloper. There attitude is if your ok then we are ok. And I dont even know if ATC units themselves are aware of the requirement (at least the ones around here!)
Remember Im talking strict legalitys here, not commonsense or practicality. Theres a gaping HUGE distinction.