Absolutely agree with the last para from FFF, but our query is different and didn't relate to any specific airport. However, mention of the Exeter TOMPO raises another question: Given that, as FFF says, some aircraft have poor ADFs, a better way to hold at TOMPO (and similar holds at other aerodromes) has hitherto been to use the localiser and DME, which gives a perfectly good hold. However, why not put the RNAV on TOMPO, couple it to the RMI VOR needle? Bingo! a perfectly normal single needle hold. Is this in accord with ICAO? Leading on from this, as more commercial air transport flights are using the same RNAV approach as training aircraft we sometimes need somewhere to "park" the trainer. We think a logical answer is a hold at the initial fix for the RNAV procedure with an inbound in line with the initial track of the procedure. Again the RNAV/RMI combination will give a perfectly good single needle hold. Does this meet ICAO requirements? Until some kind person tells us where to find this information we are a bit stuck!