How to classify "new advanced aircraft"
I am working with a group involved in the development of criteria for instrument procedures. Manufacturers and operators have been asking for the current design criteria to be updated to reflect the capabilities of modern “Advanced transport aircraft”.
This class of aircraft might benefit from smaller lateral and vertical approach volumes for precision approaches, but should certainly benefit from reduced height loss values. The current PANS-OPS criteria is based on a errors relating to direct drive altimeters (1968 Report of the UK All Weather Operations Committee). The hysteresis of these is claimed to be eliminated with modern piezoelectric sensors. Just this improvement alone would reduce OCA/H values by 9m.
The problem is how best to identify this class of "advanced" aircraft. So far four possible definitions have been suggested:
1) RVSM approved aircraft – these aircraft must have modern altimeter systems. Unfortunately the altimeter specification is geared to performance above 29000 ft and is not expressed in a way that is easily translated into mean and standard deviation values at normal instrument procedure altitudes.
2) RNP approved aircraft – unfortunately the standard RNP criteria deals only with lateral performance and even 0.1 RNP is large compared with current precision approach criteria. The upcoming RNP/AR (ICAO version of the FAA-SAAAR criteria) does contain a more stringent altimeter error requirement. However, the rather extensive aircraft and operational approval requirements mean that the number of approved operators is likely to be small.
3) Aircraft first certificated after 1982. Various sources have suggested that all such aircraft would have improved altimeter systems (at least for Part 121 aircraft).
4) Aircraft equipped with dual digital ADCs.
If anyone has comments or alternative suggestions, now is the time such advice would be very useful.
As a postcript, you may not know that the current height loss values come from a dynamic model devised by W.J.G. Pinsker of Aero Flight, RAE Bedford. Unfortunately he never explained how he derived the model - it came to us as a graphical solution which was implemeted in a monte-carlo FORTRAN program. It is only this year that we have obtained the full theoretical explanation, plus an update. This came from Dr. Radislav Danilov, of the Russian aircraft certification authority. It transpired that he had written his doctorial thesis on Pinsker's model some 20 years ago. Pinsker died in 1998, and you will be pleased to hear that his family are happy to know that his work continues to be remembered.