All Weather Operations — Page 61, Lesson 96

I want to walk you through two important pieces of All Weather Operations: the definition of a Hybrid Head-up Display Landing System, and then the rules for take-off minima. Let's start with the system definitions. First, we have the Hybrid Head-up Display Landing System, often abbreviated as hybrid HUDLS. This is a system that combines two independent parts. The primary part is a fail-passive automatic landing system — that means it can fly the aircraft down to the runway automatically, and if it fails, it does so without causing a dangerous deviation; it simply stops providing guidance in a safe way. The secondary part is an independent HUD/HUDLS — a separate head-up display system that the pilot can use to complete the landing manually after the primary system has failed. So the hybrid HUDLS gives you a backup: if the autoland fails, the pilot still has guidance on the head-up display to take over and land by hand. There's an important note here: that secondary independent HUD/HUDLS typically provides guidance in the form of command information — that means it tells the pilot what control inputs to make, like "pull up" or "steer left." But alternatively, it may provide situation (or deviation) information — that means it just shows where the aircraft is relative to the desired path, and the pilot has to figure out the corrections themselves. Next, we have the Enhanced Vision System, or EVS. This is an electronic means of displaying a real-time image of the external scene using imaging sensors. In plain terms, it uses cameras or other sensors to show the pilot what's outside the aircraft on a display, even in low visibility conditions like fog or darkness. Now let's move to take-off minima. These are the minimum weather conditions required for a take-off to be legal. The operator — the airline — must establish take-off minima expressed as visibility or RVR limits. RVR stands for Runway Visual Range, which is a more precise measurement of how far a pilot can see along the runway, measured by instruments. The minima must take into account all relevant factors for each aerodrome planned to be used and the aeroplane's characteristics. If there's a specific need to see and avoid obstacles on departure, or for a forced landing, then additional conditions like a ceiling — that's the height of the cloud base — must be specified. Here's a key rule: The Commander shall not commence take-off unless the weather conditions at the aerodrome of departure are equal to or better than applicable minima for landing at that aerodrome — unless a suitable take-off alternate aerodrome is available. So if the weather at your departure airport is below the minimums needed to land back there after an aborted take-off, you need to have an alternate airport you can divert to. Another rule: when the reported meteorological visibility is below what's required for take-off, and RVR is not reported, a take-off may only be commenced if the Commander can determine that the RVR or visibility along the take-off runway is equal to or better than the required minimum. So the pilot has to personally verify that the visibility on the runway is good enough, even if the official weather report says it's worse. Similarly, when no reported meteorological visibility or RVR is available at all, a take-off may only be commenced if the Commander can determine that the RVR or visibility along the take-off runway is equal to or better than the required minimum. Again, the pilot must make that determination themselves. Finally, the purpose of take-off minima: they must be selected to ensure sufficient guidance to control the aeroplane in the event of both a discontinued take-off in adverse circumstances — that means aborting the take-off in bad conditions — and a continued take-off after failure of the critical power unit. The critical power unit is the engine whose failure would most adversely affect the aircraft's performance. So the minima are designed to give you enough visual reference to handle either an aborted take-off or a continued take-off with one engine failed.