View Full Version : RVR vs CMV


annita
18th Nov 2010, 15:15
Whats is the difference as I cant find it somewhere and why A,B aircraft use in some approaches RVR while C and D CMV.

Thanks



galleypower
18th Dec 2010, 20:31
To my humble aviation knowledge, RVR is derived from RVR measuring equipment, and the CMV can be converted from a reported visibility.

Converted Meteorological Visibility (CMV). A value (equivalent to an RVR) which is derived from the reported meteoro-
logical visibility, as converted in accordance with the requirements in this subpart.

But what I am also trying to find out for a while is, why is CMV only used in conjunction with CAT C & D aircraft?

Anyone?

Baseomania
14th Jan 2012, 17:36
what my observation is that general visibility requirement for C & D is more then 1600 m or so above which RVR is not reported. You need to derive it from reported visibility.that is why CMV.

777-Aviator
15th Jan 2012, 14:51
That's true Baseomania!

RVR is not reported if CMV is more than 1500m.. Which means that RVR is not necessary for Cat C & D since their minimum Vis. requirement exceeds 1500m!

slav4o1
15th Jan 2012, 14:59
And just to complete the picture..out of EU-OPS

http://media.snimka.bg/9931/026118251.jpg?r=0

ExpeditePlease
24th Feb 2012, 17:52
But can CMV be used for planning purposes using TAF? JAR-OPS isn't so clear on this issue. So can I convert met vis from a TAF of my destination or alternate to the required RVR, for planning?

truckflyer
25th Feb 2012, 01:03
I am a bit confused by your posts here. I am not sure if you have been able to define your question correctly in this case.

RVR depends on what type of approach, visual, Non Precision, Cat 1, Cat 2, Cat 3 A, B and C.

On your approach plate it is normally always given in RVR.

If RVR less than 1500m, than this will be reported in the METAR, not the TAF.

If no RVR in the METAR, than that means the RVR is over 1500 m.

You will use your TAF for planning purpose, but to know if you are legal, you will have to convert it to RVR. This figure decides of how you plan your alternates.

Also the type of approach you are planning what the criteria will be for your alternate.

Example your approach is CAT II/III, your planning minima must be for CAT I RVR, for a Non Precision, planning minima are Non Precision RVR + 1000 m, MDH + 200ft

If you are not given a RVR, you use CMV for planning purpose.

Cat. A, B, C and D aircraft will have different RVR criteria depending what kind of approach your are talking about!

As far as I can recall CMV can not be used for Take off planning, but will need to revise to confirm this.

In addition for Non Precision approach you also need to take into account the cloud ceiling for planning, must be at or above MDH.

ExpeditePlease
25th Feb 2012, 10:49
Truckflyer

Yea you're right, I was also confused reading my post but your reply addressed the issue I was trying to nail.

The thing is, you say "if you are not given a RVR, use CMV for planning purposes.", but no where in JAR OPS does it say this can be done for planning.
If I'm wrong please point me in the right direction.

JAR OPS 1.430 sub paragraph L and table 11 is as close as I can get.
Notice CMV is based on REPORTED met visibility and not forecasted.
It seems to me met Vis would have to be directly translated to RVR to make a flight legal. 600vis = 600rvr.

Ep


(l) Conversion of reported meteorological visibility to RVR/CMV.

1. An operator must ensure that a meteorological visibility to RVR/CMV conversion is not used for takeoff, for cal-culating any other required RVR minimum less than 800 m, or when reported RVR is available.

Note: If the RVR is reported as being above the maximum value assessed by the aerodrome operator, e.g. “RVR more than 1 500 metres”, it is not considered to be a reported value for the purpose of this paragraph.

2. When converting meteorological visibility to RVR in all other circumstances than those in subparagraph (l)1. above, an operator must ensure that the following Table is used:

Table 11

Conversion of met visibility to RVR/CMV

Lighting elements in operation RVR/CMV = Reported met. Visibility ×

Day Night

HI approach and runway lighting 1,5 2,0

Any type of lighting installation other than above 1,0 1,5

No lighting 1,0 Not applicable

truckflyer
25th Feb 2012, 18:51
I think your point 2 confirms this with regarding planning purposes, to use CMV when no RVR is presented or available.

When no RVR is reported, you will use CMV to know what this number would be in RVR.

The table tells you what conditions apply for RVR vs CMV, and must be used for planning purpose.

All other circumstances besides take off, this means your approach etc.

Normally you will need to concentrate about Visual, Non Precision and Cat 1, as your normal approaches.

If you during flight get Visibility given, you will need to convert it to RVR to know if you are above your minima.

Example single pilot Cat 1 approach requires 800m RVR, if you recieve a met report in your TAF where your visibility is 600m, then you need to use the table to see if you will be legal. Normally RVR will be given in METAR and ATIS, however you might be interested to know how it is going to be, as the TAF is a forecast, and the METAR is actual conditions, which might not require and RVR report at current time.

If your TV says that during your approach time, visibility will be 600m, you need to use this for your planning, and use the CMV to get your RVR calculations correct. If your approach has HI Int. light in night, you will multiplie the 600 with 2 and have an RVR of 1200m, however if you doing approach at daylight, and no Hi Int. approach lights available you can only use the factor 1, so your RVR will be 600 m, so you will not be legal to start the approach after FAP.

Now if in Daylight with Hi Int. app light, factor will be 1.5, this means 900m RVR, so you could legally plan for that approach.

Note however that a METAR with a TREND in the end, will take priority ahead of any forecast in the TAF, in that first 2 hour period which the TREND is valid for.

You have to think a little of the situations when you would need to use the conversion, the table is given in JAR OPS, so that you know how to convert any Visibility distances given to useful RVR measures. If you was not going to use it, it would be useless for them to put the table in the Ops. Also it specifies when to NOT use it, so besides this you can use it all the time, unless you have RVR, but you will most likely never have the RVR during planning part of flight (as only in METAR and ATIS)

KazohiroNakamura
4th Mar 2013, 14:04
An Operator should ensure that a meteorological visibility to RVR conversion is not used for takeoff, for calculating any other required RVR minimum less than 800 m, for visual/circling approaches, or when reported RVR is available.

When converting meteorological visibility to RVR in all other circumstances than those in
sub-paragraph above, an operator should ensure that Table below is used:

The only time you can use converted visibility is:
a) No RVR measurement available and either
b) CAT I ILS, or
c) Straight-in NPA

Assume for the moment that you want to land somewhere and there is no RVR available. You only have the visibility of 275M at night with HI app lights.

Your minimums are 550m 300M mid-end and 300m stop-end.

Are you allowed to convert the visibility to 550RVR ? 275x2

So for take off you can't use CMV if the visibility is less than 800m but what about if
you are already in the air?