Low visibility is a system of conditions

Why can the same RVR support one operation and prohibit another?

Assess low-visibility capability using runway information, aircraft equipment, crew qualification, approvals and the required visual references.

Understand the mechanism

Runway visual range describes visibility along the runway under the reporting system; it is not a guarantee that a particular visual reference will be seen from a moving cockpit at a particular height. Operating minima depend on the applicable operation, aircraft equipment, ground facilities, crew qualification and approval. A single visibility number cannot establish the whole operation. In low visibility, ground movement and runway protection can become limiting before the airborne phase begins.

Decision altitude or decision height defines a decision gate within the applicable instrument approach procedure and aircraft operation. Minimum descent altitude or height belongs to a different approach structure. The required visual references, continuation conditions and missed-approach actions must be understood in that context. An automatic landing capability does not remove every monitoring or go-around requirement, and an approach clearance does not certify that the aircraft meets the operator’s minima.

Apply the evidence

Approach-ban and continuation rules contain defined measurement points and conditions. They should be taught from the current applicable rule rather than a universal claim that a flight may always continue once a number has been passed. The January 2026 ECQB update notes that some major 2021-and-later all-weather changes are outside the current objectives’ examination scope. Label an exam convention separately from current operational notes instead of silently merging the two.

Worked case · synthetic training operation

The synthetic model requires four conditions: the suppliedRVR threshold, valid ground support, required aircraft capability and qualified crew. SetRVR above the threshold while removing one required ground facility: the operation remains unsupported. Restore that facility but remove the required aircraft mode: the answer is still unsupported. The example demonstrates an intersection of conditions, not actual minima for a named approach. It also shows why “the weather is legal” is an incomplete briefing when a supporting system has failed.

How does a decision gate prevent a late improvisation?

Apply a pre-briefed continuation condition at the stated decision gate and identify when the actual aircraft state fails it.

Understand the mechanism

A decision gate links a known aircraft state with a pre-briefed continuation condition. Before the gate, the crew establish the required mode, monitoring and expected references. At the gate, continuation requires the conditions specified for that operation. If they are absent, the prescribed missed-approach or go-around procedure provides a prepared path rather than demanding an improvised decision close to the ground. The exact heights and references belong to the actual procedure.

Visual acquisition is not an all-or-nothing impression. The crew need the particular references and visibility conditions required to assess position and continue safely. A brief light or an uncorrelated bright object does not automatically establish a usable runway environment. The aircraft may also be unstable, outside the allowed configuration or suffering a relevant failure despite some visual reference being present. Each condition must support the continuation decision.

Apply the evidence

The missed approach is an active flight path with configuration, thrust, guidance and communication tasks. Expectation and role allocation reduce the delay between recognition and correct execution. A second approach requires a new assessment of conditions, fuel and alternatives; repeating the same unsuccessful attempt without a changed basis consumes margin. A training animation should make the decision branch visible before the aircraft reaches the gate, then show the consequence of the chosen branch.

Worked case · synthetic training operation

A fictional approach has a supplied gate at 200 ft and requires a stated set of visual references plus stable aircraft conditions. In the exercise those references are absent at the gate. The correct branch follows the pre-briefed missed approach; descending a little farther to search changes the exposure without establishing permission. When the references are supplied but an explicitly required aircraft condition is removed, the model again rejects automatic continuation. The 200 ft value is exercise data and must never be copied as a universal operational limit.

Can you explain and apply the mechanism?

Four original questions. Work from the stated facts, then compare your reasoning with the explanation.