All Weather Operations — Page 70, Lesson 110

I want to walk you through the visual reference requirements for Category III operations and then the circling minima. Let’s start with the visual reference rules. For Category IIIA and Category IIIB operations conducted either with fail-passive flight control systems, or with the use of an approved HUDLS — that’s a Head-Up Display Landing System — a pilot may not continue an approach below decision height unless a visual reference containing a segment of at least 3 consecutive lights is attained and can be maintained. Those lights must be from the centre line of the approach lights, or the touchdown zone lights, or the runway centre line lights, or the runway edge lights, or a combination of these. So the minimum visual segment is three consecutive lights from any of those sources. Now, for Category IIIB operations with fail-operational flight control systems using a decision height, the rule is different. Here, a pilot may not continue an approach below decision height unless a visual reference containing at least one centre line light is attained and can be maintained. That’s a lower requirement — just one centre line light, not three. Then for Category III operations with no decision height — that’s a true zero-DH operation — there is no requirement for visual contact with the runway prior to touchdown. The approach can be flown all the way to landing without any visual reference at all. Let’s move to the Category III RVR requirements table. The lowest minima an operator may use for Category III operations are set out here. For Category IIIA, the decision height is less than 100 feet, roll-out control or guidance is not required, and the required RVR is 200 metres. For Category IIIB with a decision height less than 100 feet and a fail-passive system, the RVR is 150 metres. For Category IIIB with a decision height less than 50 feet and a fail-passive system, the RVR drops to 125 metres. And for Category IIIB with a decision height less than 50 feet or no DH at all, and a fail-operational system, the RVR is 75 metres. So you can see the RVR requirement decreases as the decision height gets lower and the flight control system becomes more capable. Now let’s talk about circling. An option will always be available to make an instrument approach to one runway and then carry out a circling manoeuvre to land on another runway more suitably into wind, or to meet ATC requirements. This is called Visual Manoeuvring Circling, abbreviated as VM(C). It’s covered in detail in Air Law, but here we have the key minima. The instrument approach terminates at a defined Minimum Descent Height, or MDH, for VM(C). That MDH is maintained throughout the circling manoeuvre until you are established on visual final for the landing runway. EU-OPS 1 defines the visibility for VM(C) as shown in the table. Note that these figures are different from the requirements of Annex 6. The table gives four aeroplane categories: A, B, C, and D. For Category A, the MDH is 400 feet and the minimum meteorological visibility is 1500 metres. For Category B, MDH is 500 feet and visibility is 1600 metres. For Category C, MDH is 600 feet and visibility is 2400 metres. For Category D, MDH is 700 feet and visibility is 3600 metres. So as the aeroplane category increases — meaning larger, faster aircraft — both the MDH and the required visibility increase. That covers the visual reference rules for Cat III, the RVR minima table, and the circling MDH and visibility requirements.