Operational Procedures — Page 43, Lesson 62

Let’s start with the core concept: Aerodrome Operating Minima, or AOM. For every aerodrome you might use — departure, destination, or alternate — and for every instrument approach and runway that your operator has approved, the operator must define the applicable AOM. This is a set of minimum weather conditions required to conduct a take-off or an approach. For take-off, the AOM is the minimum acceptable met visibility — that’s the standard visibility reported in meters — or, where available, the minimum acceptable RVR or IRVR. RVR stands for Runway Visual Range, and IRVR is Instrumented Runway Visual Range — these are more precise, measured along the runway itself. For instrument approaches, the AOM consists of two parts. First, a height: either a DA/H — Decision Altitude/Height — for precision approaches, or an MDA/H — Minimum Descent Altitude/Height — for non-precision approaches. Second, the minimum applicable met visibility or RVR/IRVR. Additionally, for non-precision approaches, ICAO Annex 6 also mentions cloud consideration — meaning you may need to consider cloud ceiling as a factor. Now, let’s move to the rules for commencement and continuation of an approach. This is critical for your decision-making in the cockpit. (a) The commander — or the pilot to whom conduct of the flight has been delegated — may commence an instrument approach regardless of the reported RVR or visibility. So you can start the approach even if conditions are below minima. However, you shall not continue the approach beyond the outer marker — or an equivalent position — on a precision approach, or below 1000 feet on a non-precision approach, if the reported RVR or visibility is less than the applicable minima. That’s the hard stop. (b) Where RVR is not available, you may derive RVR values by converting the reported visibility using a table — that’s Figure 4.3, which will be reproduced in your Operations Manual. So if you only have met visibility, you can convert it to an equivalent RVR. (c) If, after passing the outer marker or equivalent position, the reported RVR or visibility falls below the applicable minimum, you may continue the approach down to your DA/H or MDA/H. So the deterioration after that point does not force an immediate go-around — you can proceed to the decision point. (d) Where no outer marker or equivalent position exists, the commander or delegated pilot must make the decision to continue or abandon the approach before descending below 1000 feet above the aerodrome on the final approach segment. If the MDA/H is at or above 1000 feet above the aerodrome, the operator must establish a specific height for each approach procedure — below which the approach shall not be continued if RVR or visibility is less than applicable minima. So you need a defined point. (e) The approach may be continued below DA/H or MDA/H, and the landing may be completed, provided that the required visual reference is established at the DA/H or MDA/H and is maintained all the way to touchdown. That visual reference is what allows you to leave the instrument segment and land visually. (f) Now, the touch-down zone RVR is always controlling. That’s the primary value. If reported and relevant, the midpoint and stop-end RVR are also controlling. The minimum RVR value for the midpoint is 125 meters, or the RVR required for the touch-down zone if that is less. For the stop-end, the minimum is 75 meters. For aeroplanes equipped with a roll-out guidance or control system, the minimum RVR value for the midpoint is reduced to 75 meters. The note clarifies: “Relevant” means that part of the runway used during the high-speed phase of the landing down to approximately 60 knots. So the midpoint and stop-end RVR matter only for that portion of the landing roll. Let me show you the conversion table for visibility to RVR, and the alternate aerodrome diagram.