Time for a Change... VEB, RNP [Real], TERPS/PANS-OPS etc
@Tom Imrich:
A/ I think when you're referring to RNP [Real], you're really talking RNP AR, which is quite different from the RNP in other PBN specs, including many which include RNP in their titles. Further, RNP AR/SAAAR also doesn't necessarily take into account non-normal ops. Designs like that are typically done by the likes of GE (ex Nav-R-us, and whose criteria are corporate and not actually compliant with any international or FAA standards); are very tightly linked to the relevant acft/config and pilot training; and are subject to special approvals by the relevant authority. And as Aterpster pointed out, this is why the specials fall into the (initial and ongoing) high cost category. Companies like QAL, Sth West etc use them for operational benefits (flexibility, transitions from ENRT, higher weight allowances for DEPs, etc) as much as they do for low approach minima.
B/ Aterpster is right about the VEB, according to ICAO and FAA criteria. And note that the standard criteria for approach designs must necessarily be based on some rules taking into account categorisation of aircraft and some factors for lowest common denominator.
Re the latter point, this is one of the reasons that the VEB is still possibly constrained, partially due to more work needing to be done to assure all (including Kentucky windage and Montreal bureaucrats) that modern baro altimeters are better than those of the 1930s. Some work has been done on this to enable RVSM, but not sufficient for assuring all and sundry that the results are suitable for lowering the fat in the VEB calcs for approach criteria (specials are always another story). Understand that this work is continuing by FAA and with international cooperation (never fast). I personally think that the PBN specs should allow for assumptions of better altitude "containment" on the VNAV path - so as to provide benefit for modern/capable aircraft. How this then info survives the publishing process and loading in to the NavDBs (some of which are already quite tight for space), and how operators/pilots know whether they can fly which procedure is a further complication.
C/ I'd suggest the "air carrier Baro based Cat II, in the 707 DC8 era" were done with very well trained pilots in an organisation which had an appreciation of risk that was very different from that which would be regarded as acceptable for RPT and even freight dog operators.
D/ The future will incorporate RNP (with or without the RF turns and with or without AR component) approaches to xLS (also with or without curves). This is what will provide best outcomes in terms of lateral and vertical precision (approach, early missed) and minima.
E/ Agree long past due "Time for a change", but it is happening (albeit too slowly).
F/ In addition to ANSPs and AIS/charting/briefing organisations, airports and local municipalities need to be part of the total equation in terms of maintaining suitable landing (and nearby) environments - eg, working VGSI, trees and other obstacles. Further, the lower the minima, the higher the total operating requirements - more and better the equipage for all acft that will use such approaches, better trained pilots (hopefully those who also know how to fly by the seat of the pants as well as knowing how to follow troubleshooting checklists, tight(er) SOPs, and more knowledgeable and competent FOPs ppl in the regulators so they can help assure that all operators are just as good as yours.
In all, sometimes the minima comes down to what risk is everybody prepared to take.
Finally, this thread drift, interesting as it is and hopefully educative for some, it should probably go to (be continued in) a separate post not specific to the BMH issue.