Rvr/vis and ils cat1

[Driver170 42]

Just need some answers here.

 

what is cat1 weather when would you do it? what would you use for this, RVR or the reported VIS at the destination? i know RVR for cat1 is 550m but thats for the TDZ only, as you don't need mid point (or stop end) for CAT I.

 

So how do i know when to use CAT1 and what are the minimums...

[rondon9897 0]

Hi Vernon,

 

You can do a CAT I approach in any weather above the RVR limit but then you can do a CAT III autoland in any weather above the RVR limit too, as long as you have CAT III protection. This might happen at a quiet airport where one would wish to test the integrity of the autoland system for maintenance purposes or just practice LVP in good weather, so that you have a CAT I reversion option if something goes wrong. As you rightly say, 550m is the CAT I RVR minimum and below this you'd have to perform a CAT II/III approach, but above 550m the choice is yours. CAT I would be the standard ILS in those conditions so go for that if you want.

 

As for the minima, not quite sure what you mean there. Decision Altitude completely depends on the airport you're going into so you'd have to check the charts. Don't forget, RVR also completely depends on the airport - for example, you couldn't fly onto ILS04L for a CAT I at LFMN with an RVR of 550m (as far as I know, anyway). There isn't a CAT II/III ILS there, so in that instance you'd have to divert (Marseilles possibly).

[Driver170 42]

Hi john thanks for the response.

 

RVR 550m for CAT 1 you have to be able to see the RWY TDZ within 550m. Is this referring to when your still in the air?

 

Minimums i mean't VISIBILITY, i seen somewhere 800m this is where i'm getting confused do i use VIS or the RVR?

 

Also i found this 550/125/75 these are minimums but are they for CAT C aircraft?

[rondon9897 0]

Oh I see what you're getting at now. Visibility and RVR are quite similar, except RVR is the vis in the direction of the runway whereas the met visibility on a METAR I *believe* is the lowest visibility observed in all directions within a certain distance (don't know what that distance is). Now in FSX we don't have the ability to measure RVR so I would use the visibility on the METAR as your RVR limit. So at LFMN again, if the RVR for 04L limit is 1200m or something like that, and the METAR on your AS NEXT dialogue says vis is 800m, you should divert.

 

EDIT: Oh and yes, 550/125/75 will be the minimum RVR limit but as far as I know it doesn't matter what category aircraft you fly. If you have a Cessna 152 with CAT I ILS (unlikely), those really should be your minimum limits for a CAT I apprach (depending on the airport,as I said). That said, the end-point of the runway shouldn't really be relevant to a Cessna 152 if you're flying to a big international airport fitted with ILS.

[scandinavian13 5,192]

 

 

Visibility and RVR are quite similar, except RVR is the vis in the direction of the runway whereas the met visibility on a METAR I *believe* is the lowest visibility observed in all directions within a certain distance (don't know what that distance is).

 

Most stations over here report up to 10SM, and anything above that is simply reported as 10SM.

 

RVR versus generic VIS is more of an issue of the site taking the management. Often, the ASOS/AWOS isn't co-located by the runway for runway protections and so on. So, the measurement may be relevant to the airport in general, but not the runway specifically. RVR is specifically measured by an instrument by the runway, aimed in the direction of the runway (parallel to it).

 

 

 

RVR 550m for CAT 1 you have to be able to see the RWY TDZ within 550m. Is this referring to when your still in the air?

 

RVR 550m for CAT I would require the instrument providing the visibility (either ASOS/AWOS or RVR unit, unless "RVR" is written in the min section) to be registering 550 or greater. It has nothing to do with your own visual acquisition of it.

 

 

 

Minimums i mean't VISIBILITY, i seen somewhere 800m this is where i'm getting confused do i use VIS or the RVR?

 

You only use a specific RVR measurement when the chart says "RVR" (otherwise, you convert from the METAR). It's just like BARO versus RADIO. You only use RADIO when the chart specifies RA, otherwise BARO.

[Driver170 42]

RVR for all cat 1 app is 550m so you can continue to DA ? But you did mention 1200m is that an airport restriction or something?

 

As for 550/125/75

 

Can you explain each one so you have TDZ, MP and STOP END, just can't see how you need to brake them up? why can't you not just use the TDZ 550m and steer the A/C down the CL because you can see...

[rondon9897 0]

Sorry to confuse Vernon - 1200m is a specific limit on the ILS 04L at LFMN just as an example. Not all CAT I approaches have an RVR limit of 550m - some (like LFMN) have higher limits. The bottom line is that if you do not have sufficient visual reference by the time you reach your decision altitude, go around. You cannot perform more than two go arounds in low visibility, so if you can't get in on the second one, divert.

 

As for the 3 segment RVR reports, not all runways have 3 visibility meters. Some only have 1. From one of my manuals:
 

 

The controlling RVR is that for the touch-down zone. If reported
and relevant, the mid point and stop end RVR are also controlling.
The minimum value for the mid-point is 125 metres or the RVR
required for the touch-down zone if less, and 75 m for the stopend.
For autolands on aeroplanes with a fail operational roll-out
guidance or control system available, 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 60 knots.

 

So presumably the other limits are to make sure you can see the stop end lights ('cos if you can't you may go off the end) and the centre-line during the latter stages of the rollout.

[Driver170 42]

Quote:

 

Found this and think it may help others understand my problem

 

 

Let's say you are not LVP qualified , no LTS qualified , just flying a cessna 172 , IFR equipped , coming to land to an airport with 550/125/75 , are you allowed to shoot the approach by regulation?

Yes you may shoot the approach, because in a 172 you will be less than 60 kts before the mid-point of a multi-RVR runway, so the mid- and stop-end RVRs are not "relevant" to you.

If your landing performance indicates you will cross the mid-point at > 60 kts, then the mid-point RVR is relevant, and must at least be 125m if reported (since this is lower than the CAT I touchdown RVR requirement of 550m).

Remember, relevant means over 60 kts at that portion of the runway.

(The rules differ by country... e.g., in the FAA world only the touchdown RVR is controlling for CAT I. The mid- and stop-end RVRs are always advisory for CAT I).

Most stations over here report up to 10SM, and anything above that is simply reported as 10SM.

 

RVR versus generic VIS is more of an issue of the site taking the management. Often, the ASOS/AWOS isn't co-located by the runway for runway protections and so on. So, the measurement may be relevant to the airport in general, but not the runway specifically. RVR is specifically measured by an instrument by the runway, aimed in the direction of the runway (parallel to it).

 

 

 

 

RVR 550m for CAT I would require the instrument providing the visibility (either ASOS/AWOS or RVR unit, unless "RVR" is written in the min section) to be registering 550 or greater. It has nothing to do with your own visual acquisition of it.

 

 

 

 

You only use a specific RVR measurement when the chart says "RVR" (otherwise, you convert from the METAR). It's just like BARO versus RADIO. You only use RADIO when the chart specifies RA, otherwise BARO.

 

 

 

Thanks for the info

[Driver170 42]

Talking about different CAT landings, when does a pilot know when to shoot a CAT I II or III what are the minimum VIS ? Because RVR is when you are on the tarmac but what about being in the air

[kevinh 409]

Talking about different CAT landings, when does a pilot know when to shoot a CAT I II or III what are the minimum VIS ? Because RVR is when you are on the tarmac but what about being in the air

The visibility near the runway is what matters. It's all about what you can see as you come in to land. At 1000 ft on the ILS it doesn't matter what the vis is. By the way, it's not just RVR that matters. The cloud ceiling is also important. RVR could be infinite, if ceiling is less than 200' it's below Cat 1 minima.

 

EASA CAT minima are:

 

CAT I: 200' DA or 550m RVR

CAT II: 100' DH or 350m RVR

CAT IIIA: no DH or 200m RVR

 

CAT II RVR can be down to 300m for category D aircraft.

 

See http://www.skybrary.aero/index.php/Precision_Approach for more details.

[Propane 16]

The cloud ceiling is also important. RVR could be infinite, if ceiling is less than 200' it's below Cat 1 minima.

 

You can still commence your CAT1 approach with a ceiling/vertical visibility below 200ft. As long as you have visual reference to elements of the approach light system or runway (surface or lights) at DA, you can land, regardless of reported cloudbase/vertical visibility.

 

 

However, if the RVR is below 550m you are not allowed to even commence the approach if I'm not mistaken (approach ban). If the RVR drops below 550m while you are on the approach, I believe the general ICAO rule is that you are allowed to continue at Commanders discretion if you are below 1000ft AAL or below the OM/FAF altitude. Whether it is smart is a different thing though .

[Driver170 42]

 

 

The cloud ceiling is also important. RVR could be infinite, if ceiling is less than 200' it's below Cat 1 minima.

 

 

Not sure about that one, for an ILS app only relevant factor is the RVR. so you can proceed for a look and see. but all down to SOPs again and captains call.

 

 

 

 

JAR OPS 1 Subpart D 1.405
Commencement and
continuation of approach

(a) The commander or the pilot to whom
conduct of the flight has been delegated may
commence an instrument approach regardless of the
reported RVR/Visibility but the approach shall not
be continued beyond the outer marker, or equivalent
position, if the reported RVR/visibility is less than
the applicable minima. (See IEM OPS 1.405(a).)

(b) Where RVR is not available, RVR values
may be derived by converting the reported visibility
in accordance with Appendix 1 to JAR-OPS 1.430,
sub-paragraph (h).

© If, after passing the outer marker or
equivalent position in accordance with (a) above, the
reported RVR/visibility falls below the applicable
minimum, the approach may be continued to DA/H
or MDA/H.

(d) Where no outer marker or equivalent
position exists, the commander or the pilot to whom
conduct of the flight has been delegated shall make
the decision to continue or abandon the approach
before descending below 1 000 ft above the
aerodrome on the final approach segment. If the
MDA/H is at or above 1 000 ft above the
aerodrome, the operator shall establish a height,
for each approach procedure, below which the
approach shall not be continued if the
RVR/visibility is less than the applicable minima.

(e) The approach may be continued below
DA/H or MDA/H and the landing may be completed
provided that the required visual reference is
established at the DA/H or MDA/H and is
maintained.

Cloud base, be it a ceiling or not, can never stop you from starting either an ILS or non ILS approach. In planning stages though, you must have a legal ceiling for the airports with NPAs (or circling), but not for ILS.

[kevinh 409]

Not sure about that one, for an ILS app only relevant factor is the RVR. so you can proceed for a look and see. but all down to SOPs again and captains call.

 

 

 

 

JAR OPS 1 Subpart D 1.405

Commencement and

continuation of approach

 

(a) The commander or the pilot to whom

conduct of the flight has been delegated may

commence an instrument approach regardless of the

reported RVR/Visibility but the approach shall not

be continued beyond the outer marker, or equivalent

position, if the reported RVR/visibility is less than

the applicable minima. (See IEM OPS 1.405(a).)

 

(b) Where RVR is not available, RVR values

may be derived by converting the reported visibility

in accordance with Appendix 1 to JAR-OPS 1.430,

sub-paragraph (h).

 

© If, after passing the outer marker or

equivalent position in accordance with (a) above, the

reported RVR/visibility falls below the applicable

minimum, the approach may be continued to DA/H

or MDA/H.

 

(d) Where no outer marker or equivalent

position exists, the commander or the pilot to whom

conduct of the flight has been delegated shall make

the decision to continue or abandon the approach

before descending below 1 000 ft above the

aerodrome on the final approach segment. If the

MDA/H is at or above 1 000 ft above the

aerodrome, the operator shall establish a height,

for each approach procedure, below which the

approach shall not be continued if the

RVR/visibility is less than the applicable minima.

 

(e) The approach may be continued below

DA/H or MDA/H and the landing may be completed

provided that the required visual reference is

established at the DA/H or MDA/H and is

maintained.

 

Cloud base, be it a ceiling or not, can never stop you from starting either an ILS or non ILS approach. In planning stages though, you must have a legal ceiling for the airports with NPAs (or circling), but not for ILS.

I never said it would stop you starting an approach but it is part of the minima. The RVR might be more than enough for CAT I but low cloud below 200' will force a go around.

 

If you know all this or can find it online, why are you asking all these questions? Or did you just use the link I gave you to research further? In which case it's pretty ungrateful to lecture me in return.

[Driver170 42]

I never said it would stop you starting an approach but it is part of the minima. The RVR might be more than enough for CAT I but low cloud below 200' will force a go around.

 

If you know all this or can find it online, why are you asking all these questions? Or did you just use the link I gave you to research further? In which case it's pretty ungrateful to lecture me in return.

 

 

Don't take it the wrong way buddy its called research and helping myself and others on this matter. its good to bring up these kind of procedures as others can learn from it when they browse avsim 737 ng forum. were all open for discussion here and know one is getting lectured.

 

even with a cloud base lower than cat 1 mins 200 you still perform a landing its only on a circle procedure you need cloud base not for an ILS app

[kevinh 409]

Don't take it the wrong way buddy its called research and helping myself and others on this matter. its good to bring up these kind of procedures as others can learn from it when they browse avsim 737 ng forum. were all open for discussion here and know one is getting lectured.

 

even with a cloud base lower than cat 1 mins 200 you still perform a landing its only on a circle procedure you need cloud base not for an ILS app

What part of "Decision Height" don't you get? If you can't see the runway at DH you can't land, ILS or not.

 

No one need bother to answer your questions in future, since you claim to be raising them so others can learn.