All Weather Operations — Page 61, Lesson 94

I want to walk you through the terminology that underpins all-weather operations. These are the exact definitions you need to know for professional flying under instrument flight rules, so let's take them one by one. First, circling. This is the visual phase of an instrument approach. Its purpose is to bring the aeroplane into a position for landing on a runway that is not suitably located for a straight-in approach. In plain terms, if the instrument procedure lines you up with one runway but the wind or traffic pattern requires you to land on a different one, you break off the instrument segment visually and manoeuvre around to that other runway. The key point: it is a visual phase, so you need the runway environment in sight. Next, Low Visibility Procedures, abbreviated LVP. These are the procedures applied at an aerodrome for the purpose of ensuring safe operations during certain categories of approach and during low-visibility take-offs. The categories covered are: Lower than Standard Category I, Other than Standard Category II, Category II, and Category III approaches, plus low-visibility take-offs. So LVP is the airport's set of rules and safeguards that kick in when visibility drops below normal Category I minima. Now, Low Visibility Take-off, or LVTO. This is a take-off where the Runway Visual Range — RVR — is less than 400 metres. That's the exact threshold: if the reported RVR is below 400 m, you are conducting an LVTO, and the airport's LVP will be active. Moving to the flight control systems. Flight Control System is defined here as a system which includes an automatic landing system and/or a hybrid landing system. So it's the umbrella term covering the automation that can land the aircraft. Within that, we have Fail-passive Flight Control System. A flight control system is fail-passive if, in the event of a failure, there is no significant out-of-trim condition or deviation of flight path or attitude — but the landing is not completed automatically. Let me unpack that. If the automatic system fails, the aircraft does not suddenly pitch or roll or go out of trim; it stays stable. However, the automatic landing capability is lost. The pilot then assumes control of the aeroplane after the failure and completes the landing manually. Then we have Fail-operational Flight Control System. This is a higher level of redundancy. A flight control system is fail-operational if, in the event of a failure below alert height, the approach, flare, and landing can be completed automatically. Alert height is a defined height on the approach — if you are below it and a failure occurs, the system still has enough redundancy to finish the landing automatically. But note: after that failure, the automatic landing system will operate as a fail-passive system. So it continues automatically, but if a second failure occurred, it would revert to fail-passive behaviour — stable but requiring pilot takeover. There is also a Fail-operational Hybrid landing system. This is a system which consists of a primary fail-passive automatic landing system and a secondary independent guidance system. The secondary system enables the pilot to complete a landing manually after a primary system failure. So the primary system is fail-passive — if it fails, the pilot takes over — but the secondary independent guidance gives the pilot the cues needed to fly a manual landing, rather than having to revert to raw data only. Finally, Visual Approach. This is an approach when either part or all of an instrument approach procedure is not completed, and the approach is executed with visual reference. So you may have started an instrument procedure and then cancelled the remaining instrument segment because you have the runway or approach lights in sight, or you may never have flown an instrument procedure at all — you simply navigate visually to the runway. The defining characteristic is that you are using visual reference to the ground, not relying solely on instrument guidance. That diagram on your screen shows how these categories and system types relate to each other. Take a moment to study it — it ties the fail-passive, fail-operational, and hybrid concepts together visually.