Baro VNAV 4 (IFPP)

13.01.2011

Submission:

A small group of IFPP Members and Advisers are attempting a complete re-write of the Baro VNAV criteria. To this end the discussions on this discussion page have been very helpful, not least in highlighting the anomalies in the current criteria.

The new criteria should be based on the material in the ICAO PBN Manual, which gives a firm basis for the margins to be applied. We are aware of the ARINC 424 coding difficulties, and that the present divorce between LNAV FAF and Baro-VNAV FAP is a factor.

This is a real multi-discipline effort, and our current efforts concentrate on the system changes when vertical guidance is selected.

There are still some problems to be resolved

- The way the TSE has step changes at 5000 ft and 10000 ft which are quite penalizing. This may influence the level of probability we can allocate to the FAS and Z surface. There is also the need to develop criteria that is not too complicated.

- The way the autopilot performance is a credit for manufacturers rather than for the users.

- The penalizing effect of including the SBAS angular W surface (we may propose two sets of minima)

- Although we had hoped to produce a set of planar surfaces like ILS, this looks increasingly difficult and complicated, and we may end with side surface heights based on an adaptation of the equation for standard MOC in secondary areas but based on TSE.

After many exchanges of e-mail, we plan a two day meeting in mid January to prepare a first draft.

This is to let you all know that your comments have proved interesting and helpful to our task.

Best Regards from the Drafting Team

Robert Woodhouse – Canada