Runway visual range (RVR)

When the visibility drops low enough that landing becomes marginal, a single general figure for visibility is not precise enough. Pilots and controllers switch to a measured, runway-specific value: the runway visual range. It is one of the most safety-critical numbers in poor weather, and it is measured and reported in a particular way that is worth understanding.

This is general educational information, not operational, legal, or regulatory advice. Rules differ by authority and change over time. Always verify against current official sources and follow your operator's approved procedures.

What RVR actually is

Runway visual range (RVR) is the distance over which the pilot of an aircraft on the centreline of a runway can see the runway surface markings, or the lights delineating the runway or marking its centreline. The definition, set in ICAO Annex 3, ties it to a very specific viewpoint and target: not the general view across the aerodrome, but how far you can see down the runway you are about to land on. That makes it the right number for the moment that matters, the final stage of an approach in low visibility, when what counts is whether you will see the runway in time.

How it is measured

RVR is not judged by eye; it is measured by instruments placed beside the runway, and there are two main types, described in ICAO Doc 9328:

• a transmissometer measures how much light is lost travelling along a fixed baseline between a transmitter and a receiver, a direct measure of how the air is absorbing and scattering light;
• a forward-scatter meter measures how much light is scattered by particles in a small sample volume of air, and infers the visibility from that.

Most modern installations use forward-scatter meters, which are compact and need only a small sampled volume. Crucially, the system then converts the measured atmospheric clarity into an RVR by also accounting for the runway light intensity in use and the pilot's eye height, because a brighter light is visible further through the same murk.

RVR versus reported visibility

The distinction that trips people up is RVR versus the visibility in a METAR, and they are genuinely different things:

• Reported (meteorological) visibility is the general visibility across the aerodrome, judged against ordinary unlit objects, and reported in the METAR visibility group;
• RVR is the runway-specific distance you can see the runway markings or lights from the centreline, measured by instrument and reported separately.

Because RVR accounts for the runway lighting, it can read higher than the reported visibility, since high-intensity runway lights are visible further than unlit features in the same fog, especially at night. So a runway can have an RVR of several hundred metres while the general visibility is lower. They are measuring related but different things, and you do not substitute one for the other.

How RVR is reported

RVR is reported when the visibility or the RVR itself falls below a threshold, around 1,500 m under ICAO practice, and it appears in the METAR as an R-group: the letter R, the runway, and the value in metres. So R27/0550 is runway 27 with an RVR of 550 m. The figure is given in steps rather than to the metre, finer steps at lower values and coarser steps higher up, and it can carry:

• a tendency letter, U for upward (improving), D for downward (deteriorating), N for no change, as in R27/0550U;
• a P for more than or M for less than a value the system can measure, as in R27/P2000 (more than 2,000 m, the maximum the system reports) or R27/M0050 (less than 50 m, the minimum).

For a precision approach, RVR may be reported at the touchdown, midpoint and stop-end of the runway, because the fog is rarely uniform and the touchdown value is the one that governs the approach. US reports give the value in feet with an FT suffix instead of metres.

When RVR matters

RVR is the currency of low-visibility operations. The categories of ILS approach are defined partly in terms of the minimum RVR, and an approach's minima specify the RVR required to begin or continue it. In poor weather the touchdown RVR can be the single value that decides whether the approach is legal to fly, which is why it is measured so carefully and reported so promptly. It is the precise, runway-specific number that the coarser reported visibility cannot provide when every hundred metres counts.

What RVR does not tell you

For all its precision, RVR has limits worth understanding. It is a horizontal measure, taken at instrument height beside the runway, and it is not the same as the slant visual range down the approach, the distance you can actually see along your descending line of sight. In a shallow fog or a thin layer, you can be looking down through it on the approach and see the lights at a slant, even while the horizontal RVR is low, or conversely lose the runway in a bank of fog the touchdown sensor has not yet caught. The RVR is the best standardised number available, but it describes the air at a point, not the whole approach.

It is also a point measurement that can vary along the runway, which is exactly why a precision-approach runway reports touchdown, midpoint and stop-end values: fog is patchy, and one end can be far worse than the other. The touchdown value governs the approach, but the others tell you what to expect on the landing roll. Reading RVR well, then, means treating it as a precise but local and horizontal snapshot, and combining it with the cloud base, the trend and your own eyes rather than leaning on a single figure.

A worked example

A METAR for a foggy morning includes the group R27/0550U. Decoding it: runway 27, RVR 550 m, with an upward tendency, so the visibility down the runway is 550 m and improving. The same report's general visibility group shows 0400, a meteorological visibility of 400 m.

The two numbers differ, and now you know why: the 400 m is the general visibility judged against unlit objects, while the 550 m RVR is how far the runway's high-intensity lights are visible from the centreline, which in fog is further than the unlit view. Neither is wrong; they measure different things. For deciding whether the approach to runway 27 may be flown, it is the touchdown RVR, the 550 m, that is compared against the approach minima, not the general 400 m. A little later the report reads R27/0800N: the RVR is now 800 m and steady, the fog thinning down the runway. The single letter on the end told you which way the weather was going each time.

Common pitfalls

• Treating RVR and reported visibility as the same. RVR is runway-specific, instrument-measured and lighting-dependent; the METAR visibility is the general view.
• Ignoring the tendency letter. U, D and N tell you whether the RVR is improving, worsening or steady, which matters as much as the value.
• Forgetting the units. RVR is metres in the ICAO form and feet with FT in the US form; read the suffix.
• Using the wrong runway position. Touchdown, midpoint and stop-end values can differ; the touchdown value usually governs the approach.
• Reading P and M as digits. P means more than and M means less than the measurable limit, not a value to use directly.

In Pilot EFB

Pilot EFB shows the decoded weather alongside the raw report, so the RVR group is explained in plain language while the original text is always kept, the same way it handles the rest of a METAR. A briefing you have already pulled stays readable away from a signal, and pulling a fresh observation needs a connection. Pilot EFB does not measure RVR or set your minima, and it is not a certified Electronic Flight Bag, so treat it as a study and planning aid and brief from your official source of record.