Its a tricky one. You arrive on the Tarmac faced with a shoddy aircraft which gives rise to a real uneasy feeling as you walk towards it. What do you do? Forfit your holiday or take a chance?
Personally whenever I book a holiday with a tour operator (sadly not too often these days!) I always ask who aircraft operator will be. Any reputable tour operator these days will have their aircraft operators 'signed' up for the seasons in question. They should also audit these operators as part of a quality system to ensure their suppliers are safe.
If one the day the flight operator cant provide an aircraft for the flight, for whatever reason, they will sub in an alternative. Again any reputable airline these days will only sub work out to a list of approved suppliers, again audited to ensure they meet with all safety requirements under JAR-OPS.
In actual fact JAR-OPS specifies that the charter of other airlines by an AOC holder must meet certain requirements.
One of which is that if the operator is not a JAR operator then permission must be obtained from the authority. In our case the CAA. Of course this applies to an 'aircraft operator' so Im not sure what rules apply to a tour operator and I guess that is the probelm.