Bristol Airport (EGGD) has the following NOTAM in place:


Would aircraft be allowed to continue approaches into Bristol? If so, would the touchdown and mid-point RVR values suffice to decide whether the approach is legal (see Approach Ban below). For example, the listed RVR minima for the RNP Approach runway 27 is 1400m (LNAV) - if the touchdown point and mid point RVR values were above this, could someone legally proceed with the published approach.

The UK AIP describes the Approach Ban as follows.

AD 4.9 Approach Ban - All Aircraft

4.9.3 An aircraft may commence an instrument approach regardless of the reported RVR/Visibility but the approach shall not be continued below 1,000 FT above the aerodrome if the relevant RVR/Visibility for that runway is at the time less than the specified minimum for landing.


4.9.6 The touchdown zone Runway Visual Range (RVR) shall always be controlling.


1 Answer 1


To perform an ILS CAT I approach, at least the touchdown zone RVR sensor must be operational. For CAT II, you need the touchdown zone and midfield sensors, and for CAT III you need all three. As per your NOTAM, if only the stopend RVR sensor is out of service, it should be possible to perform CAT I and CAT II approaches (assuming those are available for that runway in the first place).

There are procedures which allow aircrews to perform a CAT I ILS based on meteorological visiblity alone, using a special conversion table to estimate RVR values based on visiblity, but I believe those are company specific.

RVR can also be measured manually, but I am not sure this is actually allowed anymore. It would require someone to physically go to the end of the runway, and then count the number of runway lights visible from the end. Given there is a fixed distance between runway lights, you could then multiply the number of visible lights with the distance between them to get the RVR.

Not sure what the rules are for RNP approaches, but I would imagine they are similar to those regarding ILS.

  • $\begingroup$ In the U.S., under Part 121, you can fly an approach Cat 1 with all RVR transmissometers inop as long as the prevailing visibility is at/above the minimum required (typically 1/2 SM if everything else like approach lights is working). The first half sentence of your 2nd paragraph is spot-on; the rest, not as much. $\endgroup$
    – Ralph J
    Nov 1, 2020 at 4:57
  • 1
    $\begingroup$ @RalphJ Probably depends on the country. Feel free to downvote and/or provide an alternative answer $\endgroup$ Nov 1, 2020 at 7:50
  • $\begingroup$ Many thanks. @expeditedescent You can also ascertain RVR from a visibility conversion: “Where the RVR is not available, RVR values may be derived by converting the reported visibility” (CAT.OP.MPA.305 ). This derivation is achieved through the conversion table: EASA AMC10 CAT.OP.MPA.110 Table 8 Conversion of reported MET VIS to CMV. $\endgroup$ Nov 1, 2020 at 8:44

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