All Weather Operations — Page 65, Lesson 104

I want to walk you through the visual reference requirements and the different categories of instrument approaches in all-weather operations. Let's start with what you need to see to continue an approach below the minimum descent altitude or minimum descent height. A pilot may not continue an approach below the MDA or MDH — that's Minimum Descent Altitude or Minimum Descent Height — unless at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot. These references include: elements of the approach light system, the threshold itself, the threshold markings, the threshold lights, the threshold identification lights, the visual glide slope indicator, the touchdown zone or touchdown zone markings, the touchdown zone lights, runway edge lights, or other visual references accepted by the Authority — that's your national aviation authority. Now let's talk about required RVR — Runway Visual Range. A non-precision approach, or NPA, is an instrument approach using any of the facilities described in Figure 5.4, which is labelled "System minima." An NPA has an MDH or DH — Decision Height — not lower than 250 feet, and an RVR or CMV — that's Converted Meteorological Visibility — of not less than 750 metres, unless accepted by the Authority. An APV operation is an instrument approach that uses both lateral and vertical guidance, but does not meet the requirements established for a full precision approach and landing operation. APV stands for Approach Procedure with Vertical guidance. It has a DH not lower than 250 feet and a runway visual range of not less than 600 metres, unless approved by the Authority. For approaches, the RVR must be greater than the minima at the threshold. For take-off, all three RVR values must be within limits. Now let's move to Precision Approach Category I operations. A Category I operation is a precision instrument approach and landing using ILS — Instrument Landing System — MLS — Microwave Landing System — GLS, which is GNSS/GBAS Landing System using Global Navigation Satellite System and Ground-Based Augmentation System — or PAR, Precision Approach Radar. The RVR for a Category I approach must not be less than 550 metres, unless accepted by the Authority. An operator must ensure that the decision height used for a Category I precision approach is not lower than any of the following: the minimum decision height specified in the Aircraft Flight Manual, or AFM, if stated; the minimum height at which the precision approach aid can be used without the required visual reference; the OCH or OCL — that's Obstacle Clearance Height or Obstacle Clearance Level — for the category of aeroplane; or 200 feet. A pilot may not continue an approach below the Category I decision height unless at least one of the visual references I listed earlier is visible. Finally, the minimum RVR, CMV, or visibility for Category I, APV, and non-precision approaches can be derived from the following formula: Required RVR or visibility in metres equals the quantity DH or MDH in feet multiplied by 0.3048, divided by the tangent of alpha, minus the length of the approach lights in metres. Alpha is the calculation angle, with a default value of 3 degrees, increasing in steps. Let me show you the system minima table and the exceptions that go with it.