Visual descent point 1

25.10.2004

Submission:

Judging by our experience in NZ, and Gerhard's point 4., a few misconceptions exist among the operators:

1. When flying the stabilised approach, MDA can be treated as DA.

2. Aircraft should be able to do a strait-in landing if the required visual reference is achieved at any point up to, and including, MAPt

3. When visual reference is not established at MDA, an aircraft on a stabilised approach has to level off and maintain MDA to MAPt, before commencing the go around.

None of the above is true.

If the guidelines from Doc 8168, Part III, paragraph 7.1.9 are followed and location of MAPt is kept between the point of intersection of the nominal 5% descent gradient and RWY threshold, the following will be true:

1. In all cases where the along track position of the aircraft can be continuously monitored by the crew, a stabilised descent is possible and strongly recommendable

2. The stabilised approach profile following the nominal descent gradient will ensure the MDA is reached before or, in the worst case, at MAPt.

3. Descent below MDA on a non-precision approach is allowed only when the required visual reference for landing is achieved. No allowance is provided for the loss of height during the level off. It is the responsibility of the operator to ensure that level off is initiated at the height sufficiently above the MDA so that OCA is not infringed.

4. MAPt is the last point at which the missed approach procedure must be initiated, not the last point from which a strait-in landing is possible.

5. MAPt need not be crossed exactly at MDA. It must not be crossed below the MDA, but the climb can be initiated earlier, at the discretion of operator (pilot).

6. Properly executed descent will bring aircraft to the approximate (it is a non-precision approach after all) point of intersection of the nominal descent gradient and OCA (MDA). If visual reference is not established, missed approach climb can be initiated immediately.

VDP belongs to US TERPS standards. It has an obstacle evaluation area associated with it and, unless we use TERPS for the design of our approach, I suggest we leave it there.

If a procedure is tailor-made for the specific operator, who insists that the MAPt is located at the point where OCA intersects the nominal flight path, then please your customer. However, procedures are usually designed for a range of aircraft with various levels of sophistication. Those at the lower end of the scale, with only basic navigation equipment, may benefit from MAPt being closer to the threshold. Those not willing to be exposed to a level flight at low altitude, can still implement their own operating practice, provided they do not go below the prescribed MDA and observe all other limitations and requirements of the published procedure.

Obrad Puskarica

Senior Navigation Procedures Specialist _ Airways Corporation of New Zealand