Rvr and ils cat1

[michelda]

Hi guys,
Look at this situation.....

The airport has only cat 1 ils (One each rwys) and there are 2 rvr readings. One at touch down rwy 24 and the other at mid point.
If I have to land for rwy 06 and there is low vis...... I have to use mid rvr or converted vis or..... I don't know....
Thanks for tour help

Michelda

[Mike Rosewhich]

You don't need mid point (or stop end) for CAT I.

[Olympian]

As you mentioned there is only ILS CAT I approach available. So there is no point to talk about Low Visibility Ops at that airport.

And as I can recall on CAT I operations the RVR system for the first part is not even needed.

[BOAC]

Generally speaking it can be replaced by mid-point RVR or 'human' obs or you can convert met vis.

Don't you have an ops manual???????????????????????

[michelda]

Hi Mike
I know, but if I have to land for rwy 06.....


Hi Olympian
I think I need rvr or converte vis for touch down point

Thanks for your answers

Michelda

[Mike Rosewhich]

Ahh, see your point now. The generic table I read in my ops manual states you don't need a touchdown RVR assessment system.

So I guess you use something else instead, like converting met viz (but not below 800m), or perhaps the other end RVR would provide a better idea.

Sorry I can't be more definitive.

[Mansfield]

RVR transmissometers are pointed in one direction...they are not valid for the opposite runway. In your situation, runway 6 has no RVR, so the prevailing visibility is all you have.

[411A]

RVR transmissometers are pointed in one direction...they are not valid for the opposite runway. In your situation, runway 6 has no RVR, so the prevailing visibility is all you have.

Precisely.

Cat 1 means you need 550m

I think this reply needs a bit more thought...with no RVR.

[BOAC]

Still waiting for Michelda to tell us whether he/she HAS an Ops Manual and if so what it says!

I repeat - normally MIDPOINT IS ACCEPTABLE.

[411A]

I repeat - normally MIDPOINT IS ACCEPTABLE.

NOT in the opposite direction, it isn't.
Look on the approach chart, the minima will be specified for the particular runway in use.
IF no RVR for the landing runway is available...no other RVR for another runway is acceptable.

BOAC I can understand...he always seems to have an oddball obtuse opinion.
IE: to be expected..

For others...read your individual airline's Ops Specs....as therein will tell the tale.

NB.
And this brings me to another scenario...IE: those pilots who are too darned lazy to actually read and understand their airlines individual operations specifications, provided by their respective carrier....and come to some rational conclusion.
IE: those that contribute to PPRuNE on the tech forum might have no idea about those ops specs, so...can only provide general guideance.

IE: specific questions require specific details about the concerned regulatory authority....as without same, only general guideance can be obtained.

[spekesoftly]

NOT in the opposite direction, it isn't.

If we are referring to IRVR, the mid-point reading will be the same for runway 24 and 06. The atmospheric opacity at the runway mid-point is measured by the same transmissometer. Or is it different in the USA?

[BOAC]

I guess, ss, they probably have an extra portable transmissometer to put in place everywhere before big boy arrives?

[Topper80]

In eu-ops and my carrier manual:
CAT I: In case of failed or downgraded...... TDZ RVR assessement system.... no effect on applicable minima

so to get the required 550 RVR I will use the table to converts general visibility in RVR/CVR

in case of CAT II-III ops I can use mid RVR in according to national regulations


Are RVR report only valid in one direction? never knew..... Nice!

[Mansfield]

I don't believe you can get an RVR report that is not preceded by a runway number. RVR is predicated on a number of variables, but I understand ambient or background lighting to be one of them. If a particular piece of concrete has the city center off one end, and a forest off the other, each direction may have very different RVR values with the same mist falling.

That said, I'm not sure how forward scatter technology plays into this.

The directional issue is an old departure trick in the States. If you have suitable tower visibility for takeoff, but the RVR for the departure runway is below minimums for takeoff...well, assuming calm winds, you simply taxi around to the other end, the one without RVR, and use the tower visibility as your legal takeoff visibility report.

[Spitoon]

Originally Posted by Olympian

As you mentioned there is only ILS CAT I approach available. So there is no point to talk about Low Visibility Ops at that airport.

Maybe true from the aircraft perspective but airports will often start putting low visibility procedures in place at anything from 1500m vis or, sometimes, when vis is unlimited but there is low cloud about. Trouble is you can never be sure because ground LVPs are one of the most unstandard things around!

[michelda]

Thanks to everyboby
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......with minimum fuel (forcast was cavok). I diverted to my altn (forcast cavok And real wx cat2).........

Hi BOAC
I know my ops manual (it says to convert vis to rvr)......but sometime is no so easy take decision....

Michelda

[Sir George Cayley]

Got an A/P? Got an HUDLS? Then Less than CAT l could be for you.

See Annex ll of Eu Ops 1

Sir George Cayley

[DFC]

RVR transmissometers are pointed in one direction...they are not valid for the opposite runway.

Ha Ha Ha. Nice try!!

as someone else said, RVR transmissometers measure the opacity of the atmosphere between the sender and the receiver and work out an RVR.

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.

As many Garwick operators will remember, the RVR at the sensors can be 50m while the runway is CAVOK!!

If there is no touchdown RVR then use CMV to check if you can shoot the approach.

The mid-point (and stop end) RVRs are not limiting in terms of shooting the approach. However, they are indeed of interest when it comes to roll-out and if one expects to pass the midpoint at more than 60Kt then one would expect to have an RVR in excess of the take-off minima. One will usually be at less than 60Kt before passing the far end touchdown point so something like 75m can be acceptable. (All subject to appropriate LV-Ops approval).

So in the example given, I would use the vis to get a CMV and use that as the touchdown figure and then use the approved figures eg 125m (take-off minima)for the mid-point and 75m for the stop-end as minimums.

If there are are no RVR reports then you use CMV for the touchdown and that is it.

[9.G]

DFC, I agree with all the aforesaid. RVR 125 is indeed relevant for this approach, so far one reported, to perform manual auto rollout as a auto rollout accuracy isn't warranted on CAT I ILS. Doesn't mean one wouldn't use the automation to perform however in case the A/P screws up taking over manually means min RVR 125. RVR 75 M is only required to accomplish taxi, here comes towing to the stand as an option to my mind or if able to vacate the RWY within the 2/3 stopend RVR isn't needed at all. Regarding the substitution of TDZ by MID all depends on the approved Specs of the operator. If NO RVR is reported simply do the math and see if it's possible to shoot the approach.

Here's the reference in case EU OPS 1.400/1.4005

The touch-down zone RVR is always controlling. If reported and relevant, the mid point and stop end RVR are also controlling. The minimum RVR value for the mid-point is 125 m or the RVR required for the touch-down zone if less, and 75 m for the stop-end. For aeroplanes equipped with a roll-out guidance or control system, the minimum RVR value for the mid-point is 75 m.
Note. “Relevant”, in this context, means that part of the runway used during the high speed phase of the landing down to a speed of approximately 60 kt.

[BOAC]

Michelda - several things come into play here.

1) Why not ask the airport themselves - they will know whether state regs permit use of mid-point as per EUOPS (Table 6a)

2) I would suggest that the airport management may need a kick up the backside if they are offering an ILS with no touchdown RVR in low vis when they could deploy an observer (same table)

3) If your Ops Manual does not have the mid-point alleviation you are stuck with CMV, but I would ask your ops dept. to put it in (if you are EUOPS)

Lastly, what sort of 'low vis' did you have in mind in your question?