Air Traffic Controller Discussion With a Global Perspective
By Mats Edvin Aaro 1227980
#529047
Andreas Fuchs 810809 wrote:In LowVis I always have to taxi forward to the threshold


Aah, I think you did. Of course there might be other procedures in LVP, but I didn't mention LVP anywhere. :P My point was that whether or not you need to taxi forward to the threshold Depends on the type of displaced threshold, i.e. runway markings… :) But i see what you mean!
By Andreas Fuchs 810809
#529048 All good :D

I just called my flight training manager and he will talk to his examiners to find out about these Low Vis Procedures. I suspect that the main reason is not the runway identifier itself, but the spacing between the centerline lights. If we cannot be sure what the distance between them is, we cannot assess the current RVR.
By Magnus Meese 997444
#529113 Counting lights? Is that common? Are IRVRs that unreliable? I mean, there's a reason they've mostly replaced human obs, right? Also, are there no countries that file differences to ICAO specs on spacing of lights, and if so, do you keep track of all these differences?

APS pleb here, confused as always with things on the surface.
By Simon Kelsey 810049
#529114
Magnus Meese 997444 wrote:Counting lights? Is that common? Are IRVRs that unreliable? I mean, there's a reason they've mostly replaced human obs, right? Also, are there no countries that file differences to ICAO specs on spacing of lights, and if so, do you keep track of all these differences?

APS pleb here, confused as always with things on the surface.


Andreas will be able to answer in more depth, but in short a 90m visual segment is always required at the start of the takeoff run (6 lights at 15m spacing).

It is also permissible in some circumstances (down to 150m RVR) to replace the reported value (or if the RVR is not reported) with pilot assessment (i.e. up to 10 lights, depending on the cockpit cutoff angle etc).

The actual runway centreline light spacing is shown on the charts (and I think is ICAO standard for a CAT III runway in any case).
By Magnus Meese 997444
#529117 Thanks for the reply. I'm not really confused on runway lighting and strip stuff, I'm kind of sort of required to know that stuff anyway, though I don't apply it working radar.

My confusion is as to whether counting lights is commonplace, when most III-runways have two or three IRVRs that provide that information for you, and the tower guy/gal provides that information. Also, are there countries which have filed differences from ICAO on RW lighting, and do airlines/flight crews keep on top of that if this is the case? I know for sure countries do all kinds of stuff with taxiway lighting, so I would assume some could be inventive enough to mess about with runways as well.
By Simon Kelsey 810049
#529119
Magnus Meese 997444 wrote:My confusion is as to whether counting lights is commonplace, when most III-runways have two or three IRVRs that provide that information for you, and the tower guy/gal provides that information.


Yes - because the purpose of counting the lights is to ensure that there is a 90m visible segment in front of the aircraft (bearing in mind that the cockpit cutoff angle will mean that there is an area in front of the aircraft which is included in the RVR reading but is not visible from the flight deck), and/or to replace the measured RVR value with pilot assessment if need be (so if the reported RVR is less than the 150m required but on lining up you can count 10 lights (allowing for the cutoff angle) and have a 90m visual segment as well then the reported RVR may be disregarded).

Magnus Meese 997444 wrote:Also, are there countries which have filed differences from ICAO on RW lighting, and do airlines/flight crews keep on top of that if this is the case? I know for sure countries do all kinds of stuff with taxiway lighting, so I would assume some could be inventive enough to mess about with runways as well.


I'm sure there are but, as I say, the runway light spacing and type for a specific runway is provided on the charts for that airfield, so provided the crew have an up to date chart then they will know the spacing...

Is that what you were asking?
By Magnus Meese 997444
#529121 Mostly, thanks. I just had never registered the counting of lights as a procedure when IRVR is installed and operational, be it on the jumpseat in LVP, cockpit video, or just any old document, and thus curious to as if everyone does it considering I've not noticed it in either of those first two situations. If everyone does count them, are some/all companies doing this silently?
By Andreas Fuchs 810809
#529123 I have no idea whether all companies do it, or not. We (NJE) certainly do it and we train it each and every time we go to the SIM.
By Rob Nabieszko 1138610
#529280 As another RW pilot, yes we count lights for any RVOP or LVOP departure. This is true of 2 different companies I have worked at and would be considered a failure in the sim if you did not.

While RVR is a useful information tool, it is not located on the runway, where the visibility matters. Although unlikely, there could be variations from the runway to where the RVR equipment is located.

In Canada, the regulations state specifically that the Captain must be satisfied that the required visibility is available. Counting lights is the most reliable method on the actual runway.

As far as the original question, there is no legal requirement to taxi to a displaced threshold, though specific companies may make it a requirement.

As a controller, I would have no problem with someone using the displaced threshold, provided they COMMUNICATE this in advance. The normal expectation would be to line up at the point where you enter the runway (within 100-200 feet). I would also get very worried that someone taxiing 1000 feet or more down the runway is taking off without clearance, or could even collide with traffic crossing downfield.
By Andreas Fuchs 810809
#529288 Hi Rob,

thanks a lot for your post - I thought we were the only ones adhering to the rules...
In the meantime I have asked around and found the respective legislation that these LVO procedures are based on.
For European operators it is published by EASA: Annex to Decision 2012-019-R - AMC-GM to Annex V (Part-SPA) (corrected on 29.08.2018)

You will find the information on page 18, here's a screenshot of it:

Image

To make it short: as soon as the RVR drops below 150m the flight crew has to make sure that a visual segment of at least 90m is available. Depending on the runway/airport, the segment before a displaced threshold may not provide a spacing of 15 metres between runway centerline lights. As long as the crew is able to determine that the visual segment is 90m or greater, taxiing forward to the displaced threshold may not be necessary, but during our SIM-checks not doing so will result at least in a remark.

Another great resource is [urlhttps://www.skybrary.aero/index.php/Low_Visibility_Procedures_(LVP)][/url]SkyBrary.
By Dhruv Kalra 878508
#529299
Rob Nabieszko 1138610 wrote:While RVR is a useful information tool, it is not located on the runway, where the visibility matters. Although unlikely, there could be variations from the runway to where the RVR equipment is located.


I’m sorry, but what? RVR, the equipment that measures Runway Visual Range, isn’t located on the runway? Unless you’re referring to a scenario where you’d be on a non-RVR Runway at an airport where not all runways have RVR equipment, that statement is categorically incorrect.

https://en.wikipedia.org/wiki/Runway_visual_range
By Andreas Fuchs 810809
#529304 Dhruv,

where do you think that the RVR measurment equipment is installed: on the runway or next to the runway? We both know the answer and as a consequence we can safely say that the measured RVR does not necessarily has to be equal to the true RVR on the runway. Therefore air law regulations impose the requirement on the crew assess the situation and make sure that a visual segment of at least 90m is available.

PS: as a practical example have a look at UUWW airport (Moscow Vnukovo). The RVR sensors are located in a small ditch that runs parallel to the runway. While these RVR-metres may report a visibility that is below CAT I minima, the runway itself has a much better visibility. I had to override an ATCO there already, because they were insisting that the RVR was 400 metres, while the runway had at least 1 km.
By Alex Seeberger 1129791
#529415
Andreas Fuchs 810809 wrote:Dhruv,

where do you think that the RVR measurment equipment is installed: on the runway or next to the runway? We both know the answer and as a consequence we can safely say that the measured RVR does not necessarily has to be equal to the true RVR on the runway. Therefore air law regulations impose the requirement on the crew assess the situation and make sure that a visual segment of at least 90m is available.

PS: as a practical example have a look at UUWW airport (Moscow Vnukovo). The RVR sensors are located in a small ditch that runs parallel to the runway. While these RVR-metres may report a visibility that is below CAT I minima, the runway itself has a much better visibility. I had to override an ATCO there already, because they were insisting that the RVR was 400 metres, while the runway had at least 1 km.


Hi Andreas,

I understand where you are coming from but as far as the US is concerned, Dhruv is spot on.

The FAA does not limit displaced threshold use based on visibility. In the US, that pavement is available in all visibility conditions. Certain companies may require that they visually identify the runway identifier (or whatever they are called) but the regulations do not.

I have heard of counting runway lights before in the past. This isn’t really a thing in the US, except in novelty cases (Overachieving pilots). When RVR is taken, it typically includes readings from multiple points on the runway, here in the states. Usually from 3 points and sometimes 4 on a specific runway. I’m pretty sure one of the R’s in RVR stands for runway and those readings are given for a specific runway, not the general airport. So yes, RVR is the limiting factor regarding visibility on this side of the pond.

Just to play devils advocate :)

Regardless of the required visibility to initiate or continue an approach, at minimums the pilot must be reasonable sure the visibility is within limits, in their opinion to continue to landing. How many runway lights are required if the minimums are 550 meters? Can you reliably count that at 150 knots during a night approach:)
By Simon Kelsey 810049
#529474
Alex Seeberger 1129791 wrote:Regardless of the required visibility to initiate or continue an approach, at minimums the pilot must be reasonable sure the visibility is within limits, in their opinion to continue to landing. How many runway lights are required if the minimums are 550 meters? Can you reliably count that at 150 knots during a night approach:)


You're comparing apples and oranges.

The visual references required at DH on approach are, of course, very different to those required for an LVTO and clearly defined (at least in EASA land -- I assume also in the AIM). For a CAT I approach, that would basically be 'something' (at least one of the runway, runway threshold markings, runway edge lights, elements of the approach lighting system, PAPIs, touchdown zone markings/lights etc). For CAT II, at least three consecutive lights including a lateral element are required, CAT IIIA requires three lights, IIIB with a DH requires one light, and IIIB no DH no visual references at all are required before touchdown. I believe the USA is similar in this regard.

For takeoff, legally (EASA):

(b) for an LVTO with an RVR below 150 m but not less than 125 m:
(1) high intensity runway centre line lights spaced 15 m or less apart and high
intensity edge lights spaced 60 m or less apart that are in operation;
(2) a 90 m visual segment that is available from the flight crew compartment at
the start of the take-off run; and
(3) the required RVR value is achieved for all of the relevant RVR reporting
points;


Without counting lights, how can you ensure requirement (2) above is satisfied as it is specific to the aircraft?

I'm not sure what the FAA rules are regarding takeoff minima as I can't find a reference in the AIM and I don't know my around the FARs but presumably there must be some sort of visual reference requirement?