Baro VNAV 4 - history

30.05.2011

Submission:

A few problems with developing criteria based on the PBN Manual (or Annex 10). Back in the 1970s when the ILS criteria as developed we had data, a model and Annex 10. We also had the real performance data of the ILS system which is much better than the Annex specification. We built a data matched model based on this to extrapolate to remote probabilities. The intention was then to substitute the Annex 10 "world wide" values in the ILS system variables. The result was a disaster with OCS worse than the old 0.6 and 0.625 Theta. Thus the criteria for ILS, MLS, GBAS and APV are based on operational performance and not specifications. Now appears the PBN Manual and a brief to use it to define baro VNAV surfaces. So history repeats itself and we find the TSE values resulting in an increase of current criteria, almost unusable above 5000 ft and operationally useless above 10000 ft. It is still "work in progress" but I guess it will end very similar to current criteria but with a more reasonable start of climb and perhaps better treatment of missed approach side surface penetrations. But still "work in progress".

Robert Woodhouse - Canada