All Weather Operations — Page 56, Lesson 90

I want to walk you through the start of the All Weather Operations chapter. This is a critical area because it sets the foundation for how we determine the minimum weather conditions in which we can operate, and it begins with how we classify the aeroplane itself. First, we need to understand how we categorise aeroplanes for the purpose of determining operating minima. The key parameter here is something called VAT — that stands for indicated airspeed at threshold. This is not a random number; it is calculated from the aeroplane's stall speed. Specifically, VAT is equal to the stalling speed in the landing configuration, which we call VSO, multiplied by 1.3. Alternatively, if we use the 1g stall speed, which is labelled VS1g, then VAT equals that speed multiplied by 1.23. Both calculations are done at the maximum certified landing mass — that is the heaviest weight at which the aeroplane is certified to land. Now, here is an important detail: if both VSO and VS1g are available for your aeroplane, you must use the higher resulting VAT. So you calculate it both ways and take the larger number. That VAT value then places the aeroplane into one of five categories, which are shown in Figure 5.1. Let me read you those categories directly. Category A: VAT less than 91 knots. Category B: VAT from 91 to 120 knots. Category C: from 121 to 140 knots. Category D: from 141 to 165 knots. And Category E: from 166 to 210 knots. So, for example, a small single-engine trainer might fall into Category A, while a large jet transport like an Airbus A380 would be in Category D or E. Now, before we move into the low visibility operations, there are two fundamental approach requirements you need to know. First, all approaches shall be flown as stabilized approaches, abbreviated SAp, unless the Authority has specifically approved a different technique for a particular approach to a particular runway. Second, all non-precision approaches — that is, approaches that do not provide vertical guidance — shall be flown using the continuous descent final approach technique, or CDFA, again unless the Authority approves otherwise for a specific approach and runway. Now let's turn to Low Visibility Operations and the general operating rules. Low visibility operations consist of several specific types of operations. The first is a manual take-off, which may be performed with or without electronic guidance, or with what is called HUDLS or Hybrid HUD/HUDLS. HUDLS stands for Head-Up Display Landing System — it projects flight information onto a transparent screen in front of the pilot so they can keep their head up and eyes outside. The second type is an autocoupled approach down to decision height, or DH, followed by a manual flare, manual landing, and manual roll-out. "Autocoupled" means the autopilot is flying the approach along the guidance signals. The third type is an autocoupled approach followed by autoflare, autolanding, and manual roll-out. So here the autopilot handles the flare and the touchdown, but the pilot manually steers the aeroplane after landing. The fourth type is an autocoupled approach followed by autoflare, autolanding, and auto roll-out — but this is only permitted when the applicable RVR, or Runway Visual Range, is less than 400 metres. RVR is the distance a pilot can see along the runway surface, measured in metres. So when visibility is really low, below 400 metres RVR, you need the full automatic roll-out as well. The fifth type is an approach flown with the use of a HUDLS, Hybrid HUD/HUDLS, and/or EVS. EVS stands for Enhanced Vision System, which uses sensors like infrared or millimetre-wave radar to give the pilot a synthetic view of the runway in low visibility. Now, the precise nature and scope of the procedures and instructions given for these operations depend upon two things: the airborne equipment used and the flight deck procedures followed. The operator — that is, the airline — must clearly define each flight crew member's duties during take-off, approach, flare, roll-out, and missed approach in the Operations Manual, or OM. Particular emphasis must be placed on two areas. First, the crew's responsibilities during the transition from non-visual conditions to visual conditions — that critical moment when you break out of cloud or fog and see the runway. Second, the procedures to be used in deteriorating visibility or when failures occur. Special attention must be paid to the distribution of flight deck duties so that the pilot who is making the decision to land or execute a missed approach has a workload that allows him to devote himself to supervision and the decision-making process. In other words, the pilot flying should not be overloaded with other tasks when a go-around decision might be needed. That covers the classification of aeroplanes by VAT and the general framework for low visibility operations.