Rvr and ils cat1

[411A]

RVR is a measurament of the visual range at a point. It is not directional. i.e. RVR is a measurament of the visual range at a point. It is not directional. i.e. the RVR can be different as soon as one moves away from that point in any direction.

Therefore, [QUOTE]...the RVR can be different as soon as one moves away from that point in any direction.
It then follows that an RVR for one runway cannot be substitued for another runway, just for convenience.
Look on the approach chart.
Is an RVR value specified?
If so, it is controlling.
If not, one cannot subsitute some other RVR from any other runway...and yes, even one from the same runway, but in the opposite direction.
In addition, RVR is normally referenced to the runway light setting, and many runway lights are not uni-directional.

[BOAC]

Why not quit when you are behind?

[411A]

Why not quit when you are behind?

Because...I am correct.

[DFC]

It then follows that an RVR for one runway cannot be substitued for another runway, just for convenience.

No one is substituting anything.

Let's look at a typical runway - 18/36 with CAT 1 ils on each end.

Runway 18/36 has 3 RVR transmissometers. One placed at a point abeam the touchdown point runway 18, the next abeam the mid-point and the next abeam the touchdown point runway 36.

They indicate RVRs that are deemed to be representative of the RVR at that point on the runway.

If starting at the 36 threshold the RVR's are 100m, 300m, 600m then 99.999% of the worlds pilots will want to fly the ILS 18 because the RVRs for 18 are clearly 600, 300, 100m.

You on the other hand would be diverting unless the airport had installed a second set of transmissometers right beside the first ones. :-)

The only case I can think of where the RVR at the stop end of 36 will be different from that for the touchdown of 18 is when the lighting intensity is different in each direction since the reported RVR does take lighting intensity into account. However, most runways have bi-directional lights and thus the lighting intensity will be the same in both directions unless lights are u/s.

So while the posibility exists, it has nothing to do with the RVR sensors being directional.

[411A]

The slight problem arises, DFC, where one runway has RVR specified for approach/landing, however, in the opposite direction it does not.
In the above referenced case, RVR is available in the first instance, but not the second, even though transmissometers are installed.

IE: the chart minima applies, not some wild idea about using RVR for another runway, even IF that other runway is the same pavement but in the opposite direction.

[Meikleour]

411A:
I humbly kneel before the temple of total aviation knowledge however is it not the case that the Jeppesen symbology used to indicate the siting of transmissometers not also indicate their respective orientation?
In other words, a runway served by ILS and RVR in each direction will have its touchdown meter aligned with the relevant runway and the midpoint (if installed) will usually be aligned with the predominate landing direction. Thus the stop end reading will be from the opposite direction to the landing. Bearing in mind the above, substitution of the mid point for the touchdown may be quite appropriate.

Toodle-pip! Old boy!!

[Mansfield]

I suspect that what we have here is yet another case of everyone speaking English without realizing that they are speaking different languages. The FARs and EU-OPS appear to take a very different approach to this. This is a bit long-winded, but the more I dug around, the more I realized that the authorities are very hard to pin down on this point. Some background first:

The explanation given in paragraph 4-213 of FAA Order 8900.10, Flight Standards Information Management System, is as follows:

RVR measurements are taken by a system of calibrated transmissometers and account for the effects of ambient background light and the runway light intensity. Transmissometer systems are strategically located to provide RVR measurement associated with one or more of the three basic portions of a runway: the touchdown zone (TDZ) portion, the mid runway (MID) portion, and the rollout (Rollout) portion.

RVR is an instrumentally derived value that reflects an artificially created seeing condition on or near the portion of the runway associated with the RVR report. This artificially created seeing condition is achieved by using high intensity runway edge, touchdown zone, and centerline lights. These lights increase the conspicuousness of the landing surface and “reach out” to the pilot thereby creating a seeing condition which is significantly better than the reported ground visibility or tower visibility. For any particular fog density, RVR will be significantly greater than reported visibility because RVR is based on the use of high intensity lights. Since RVR is based on high intensity lights, an RVR report only has meaning when associated with the seeing-conditions on or near the portion of the runway where the report was obtained (TDZ, MID, or Rollout). An RVR report has no meaning unless a pilot is also seeing the high intensity lights on which the report is based.

There are, in fact, two types of RVR systems in use in the States. The older one, known as a Tasker 500, uses a projected light beam as defined in FAA Order 6560.10B, Runway Visual Range:

In the United States, runway visual range is a value determined by instruments located alongside and about 14 feet higher than the centerline of the runway, based on standard calibrations, that represents the horizontal distance a pilot will see down the runway from the approach end; it is based on the sightings of either high intensity runway lights or on the visual contrast of other targets whichever yields the greater visual range. RVR, in contrast to prevailing or runway visibility, is based on what a pilot in a moving aircraft should see looking down the runway.

The transmissometer projector and receiver are each mounted atop 14 foot towers either 250 or 500 feet apart. These towers are located at least 400 feet from the runway centerline on a line divergent with the runway centerline not to exceed 14.5˚ with the projector light beam directed angularly away from the runway. When an RVR system is installed between parallel runways and serves both runways the baseline of the transmissometer will be parallel to the runway.

Note that directionality is very much a factor here, in terms of beam direction and beam axis alignment with the specified runway.

The second system, known as the New Generation RVR, uses forward scatter meter technology. This relies on a single visibility sensor for each RVR location that measures the extinction coefficient. However, FAA Order 6560.23, New Generation RVR Program Management Plan, continues to state that RVR “represents the horizontal distance the pilot can see down the runway”.

This definition persists into the most recent FAA document, FAA-E-2772B, Performance Specification – PC Based Runway Visual Range System. This also focuses on the NGRVR using the forward scatter meter, and offers this product definition:

Product Definition: The RVR product is a calculated estimate of how far down a runway a pilot is expected to see. It is calculated using standardized equations from measurements of three parameters: extinction coefficient, ambient light level and the intensity of the runway lights. The RVR distance values shall be reported in feet.

Now, with respect to the operating rules...

FAR 121.655: Applicability of reported weather minimums.

In conducting operations under §§ 121.649 through 121.653, the ceiling and visibility values in the main body of the latest weather report control for VFR and IFR takeoffs and landings and for instrument approach procedures on all runways of an airport. However, if the latest weather report, including an oral report from the control tower, contains a visibility value specified as runway visibility or runway visual range for a particular runway of an airport, that specified value controls for VFR and IFR landings and takeoffs and straight-in instrument approaches for that runway.

Kent Jackson's explanation from his 2004 summary of Part 121 rules and Chief Counsel opinions says:

RVR or RVV controls only the particular runway for which it is installed. One cannot take off or land on a particular runway using the reported visibility for another runway. (example: You need ¼ mile visibility for takeoff on runway 24. Reported visibility 1/8 mile in fog. RVR for runway 13 is reported as 1600RVR (which corresponds to ¼ mile visibility). You cannot takeoff from runway 24 based upon the visibility for runway 13.

From what I can see of JAR-OPS 1.430, the approach taken is entirely different. Paragraph H of Appendix 1 to 1.430 lays out the use of a conversion of meteorological visibility to RVR for CAT I operations. There is no such animal in US rules; in fact, they go a long way out of their way to emphasize that RVR is not related to meteorological visibility. This may explain the divergence of opinion among colleagues on different sides of the Atlantic.

At the end of the day, however, the Federal Meteorological Handbook says that:

RVR shall be coded in the format, RDRDR/ VRVRVRVRFT, where R indicates that the runway number follows, DRDR is the runway number (an additional DR may be used for runway approach directions, such as R for right, L for left, and C for center), VRVR VRVR is the constant reportable value, and FT indicates that units of measurement are feet. For example, an RVR value for runway 01L of 800 feet would be coded:

R01L/0800FT.

So as I stated in an earlier post, I believe that RVR will always be reported with a runway number preceding it. That is the runway it is valid for.

[9.G]

Meikleour,

I humbly kneel before the temple of total aviation knowledge however is it not the case that the Jeppesen symbology used to indicate the siting of transmissometers not also indicate their respective orientation?

NOT quite so my good Sir. 10-9 clearly depicts the position and orientation of the transmissiometers along the relevant RWY. The technical measurement of the IRVR is valid for both directions however it's operational use might be restricted. The solution to the riddle is the applicable minima criterium charted on the approach plate.

DEPICTION OF EU-OPS AOM IN CASE OF EXISTING STATE MINIMUMS

If State minimums are officially published, the depiction of AOM may differ from the standard depiction where all values are expressed as RVR or CMV.

a.
If RVR/CMV and VIS are charted together, the RVR value is compulsory. If no RVR is reported, the VIS has to be used without conversion.

b.
No prefix is charted if RVR/CMV and VIS is identical. The reported RVR is compulsory. If no RVR is reported, the VIS has to be used without conversion.

c.
If only VIS is charted, the VIS has to be used without conversion.

[411A]

So as I stated in an earlier post, I believe that RVR will always be reported with a runway number preceding it. That is the runway it is valid for.

Precisely.
Therefore, one cannot use an RVR value for (using an example) runway 18, when there is no RVR reported for runway 18...but there is a reported RVR value for runway 36, IE: the opposite direction on the same runway surface.

[9.G]

So in the example given, I would use the vis to get a CMV and use that as the touchdown figure

I'd do exactly the same for the example given. By doing so the regulatory requirements are satisfied and NO reverse (18 for 36) RVR usage is accomplished. As long as we're not LVO I don't see there a big problem. Big question is what's the applicable minimum for the RWY 06? IOW simply ask the tower either RVR readings for RWY 06 or prevailing visibility and see my applicable minimum. All the other aspects are purely academical.

[BOAC]

For Mansfield also, useful info but the discussion is about EUOPS - FAA not at all relevant.

9.G - we have no idea from the OP what is 'charted' for this approach. It would be of interest indeed to know.

Certainly in view of what appears to be absent from the OP's manual, CMV would tick all the boxes.

[Meikleour]

Mansfield: Thanks for the info.I still have a query.

Take a typical ILS and RVR equipped runway serving both directions.
RVRs given T/D, Mid and STOP end
Do you agree that the Touchdown tranmissometer at each end will be orientated for the relevant ILS?
MID POINT sensor can be either direction but more commonly that of the most commonly used runway?
Now given that the MID reading will be used for either runway will its reading be different for each runway direction and if so, how is this change in reading derived?
By the same token, are the respective STOP end values modified to allow them to be used for each end?

The original poster had a situation where there were only two transmiss. for R24 (T/D & Mid) It is difficult to envisage a situation where R06 would not have had its own T/D transmiss. (u/s notamed perhaps) and as I see it he was asking whether the MID reading as measured for R06 could be substituted in lieu for T/D (his own manuals allowing?)

[michelda]

Hi Meikleour
In my country you are allowed to substitute tdz with mid point only for cat 2/3 (no our case).
As I has writen some posts ago I decided to convert vis in rvr and then fly to my altn.
Thanks for your help
Michelda

[9.G]

michelda, at the same time lack of TDZ RVR assessment has no effect on CAT I ILS approach. I presume we're talking about Napoli here judging based on the RWY directions and other particularities. If so, 10-9 under "ADDITIONAL RWY INFO" shows availability of RVR readings for RWY 24 and lack of such for 06. Perhaps it's due to LOC offset? Anyways, here te way to go would be obtaining the required RVR through conversion of prevailing visibility. As it was 400 m at night but required RVR is 900 you were short of 100 m to be eligible for approach.

[BOAC]

Interesting airport 9.G - any idea why the significant difference between Jepp normal and JAA RVRs on ILS 06?

[9.G]

BOAC,

any idea why the significant difference between Jepp normal and JAA RVRs on ILS 06?

We're talking about the state imposed minimas here. from Italian AIP

Aircraft special procedures in low visibility conditions
1) All flight operations forbidden with RVR less than 700 m due to 615 m reduced approach lighting system
2) Due to unavailability of stop bars, ACFT movements on manoeuvring area restricted to one at a time with RVR less than 550 m
3) Landing for RWY 06 is allowed as follows: a) Visibility/RVR 900 m or above with ILS approach
b) In other cases: visibility 5 Km or above and ceiling 2000 ft or above during HJ -/+ 30; visibility 8 Km or above and ceiling 2000 ft or above during HN

The reasons behind might be the glide slope of 3,5 and the LOC offset of 3 degrees not to mention displaced THR thus logically higher RVR/VIS.

[BOAC]

Its the '1400' on Jepp and '900' JAA?

[9.G]

old JAA & new STANDARD appendix stipulating new conditions for determining the RVRs taking mainly into account the ALS and many other virtues like offset etc. I presume JAA min is 900 and Standard is 1400? If so it's the transition from the OLD to the new appendix, I don't have the new plates though.

[BOAC]

"I presume JAA min is 900 and Standard is 1400" - yes - quite a change.

[DFC]

So as I stated in an earlier post, I believe that RVR will always be reported with a runway number preceding it. That is the runway it is valid for.

The argument that the RVR for 18 can not be substituted for runway 36 is corect. After all if the RVR for runway 18 is reported as 550m then one can never assume that the RVR for runway 36 will also be 550m since that threshold is a large distance from the point where the RVR 18 is measured.

However, in multiple RVR situations when the RVR is taken at 3 locations the RVR indication will be representative of the RVR at that part of the runway.

So if the RVR is reported as Runway 18 - 150, 350, 550 it is resonable to expect that the RVR for 36 - will be 550, 350, 150.

If I was to follow 411A's advice then how would I ever cope with the following:

Landing runway 36. RVR 36 = 550, 125, 75

Roll to the end required, turn in the turning circle and taxi-back to only available LVP exit at threshold 36.

411A says that if I need 75m to taxi then once I get to the turning circle I can not taxi back along the runway because while the stop end RVR 36 is 75m I can not use this as being the RVR in the opposite direction and therefore I don't have the required RVR to taxi back along the runway.............yea right!

Naples being the example chosen does not have an RVR measurament at the threshold of 06 / stop end of 24. As far as I am aware there is no authorisation for anyone to conduct lower than CAT1 approaches and therefore it is entirely logical that money is not wasted on installing and maintaining equipment that is not required. There is an ILS on 06 but this is not the preferred runway and looking at the location, when the winds require 06 to be used it is unlikely that fog / low cloud will exist.

--------------

As far as I can tell, 06 has 510 metres of approach lights and the ILS has a DH of 396.

Looking at EU-OPS, (old Appedix), CAT 1 Precision Approach, Intermediate Facilities, DH 310 and above then we need an RVR of 900m. The Italian Authorities have helpfully also done the calculation and state clearly in the AIP that an RVR of 900m is required for ILS 06.

The new appendix requires an RVR of 1400m. Until 2011 operators can continue to use the old appendix and so it will be interesting to see if ENAC changes the 900m RVR restriction to 1400m when everyone has to follow the new appendix.

So going back to what Michelda said;

It happened to me one year ago.......rvr requested 900, vis 400 (night flight) rvr mid point 200 stopend 400. Ils on other side u/s. Nice flight at 3.30 lt......

So to answer the original question - you use CMV to decide if you can make the approach (avoid the approahc ban). At DA(H) if you have the required visual references (and they are maintained) then you can continue to land.

The mid-point RVR and the RVR at the other end of the runway are of interest in terms of the roll-out and most operators will use a minimum of take-off minima for the mid-point (where the aircraft is faster than 60Kt) and something like 75m (or the taxi limits) for the other end.