RNAV trails were held a few years ago at
JS,CT and DN, involving SAA and a few other operators. As previously stated, this was done under the GROMET project. As sufficient information and data has been collected and collated, the project has been suspended (will someone please tell SAA flt ops that, so they can stop filing the comment in Field 18 iro RNAV approaches!!).
They were reasonably successful, but are limited in their use when other operators are not able to use them simultaneously. Because of the speeds and profiles that had to be flown, it was often required to make a plan for the operators to fly the arrivals.
They do work very well but one has to relate/compare them to whether they really work well at an airport with an ILS or not and then compare the cost savings. Where they will work well and speed things up is at unmanned approaches and also airports that do not have radar facilities, ie FAGG or FALA or FAYP for example.
There are very def costs savings involved but there is a lot of legislation and paperwork that needs to be completed prior to their implementation. They are very complicated to draw up and have approved. I was luckily enough to attend an IATA course on RNP operations, etc and whilst very informative and exceptionally well presented, it is evident that there is a lot of work that needs to be done by operators prior to them gaining approval to fly RNP or RNAV approaches. Costs involved include the training of crews, ensuring that a/c are properly equipped and authorised to fly the approaches and the on-going training.
Once the legislation has been met I am sure they will prove a definite saving to the operators.
Currently ATNS and CAA are involved in drawing up the approaches at several airports. This is being done on the basis of information obtained from the GROMET trials. Once they have been completed, they need to be verified and audited by another independent party (ICAO requirement) and then published. Due to a sadly lacking PANS-OPS department at CAA, it is not going according to plan, however ATNS is busy outsourcing their PANS-OPS department to NATS, so things should be moving from that side. Of course once they are published, operators are going to need approval from CAA to fly them.
AFAIK there is no-one that has been approved for this ops yet and the operators are doing them at their own risk, which also raises some intersting points, when it comes to incidents and liability......