RVR vs CMV

[annita]

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]

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]

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]

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]

And just to complete the picture..out of EU-OPS

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

[ExpeditePlease]

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]

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]

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]

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]

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?

[mauro.villani]

You cannot use the CMV to convert any metereological visibility giving you a CMV value lower than 800m nevertheless CMV cannot be use for Take.

"Straight-in approach minima are often expressed in terms of RVR. Following widely used procedures, many airline operators convert the reported meteorological visibility into an equivalent RVR value, called CMV. This conversion is applied by the pilot only for landing, when the required RVR minimum is equal or above 800 m (1/2 sm) and when the RVR is not available (a reported RVR above its 2000 m limit is considered as being not available)."

I hope this can help.

[paco]

Somebody mentioned JAR OPS. Doc 965/2012 is the current ops stuff. Maybe this will help (or maybe not!):

AMC1 CAT.OP.MPA.110 Aerodrome operating minima
TAKE-OFF OPERATIONS – AEROPLANES
(a) General
(1) Take-off minima should be expressed as visibility or runway visual range (RVR) limits, taking into account all relevant factors for each aerodrome planned to be used and aircraft characteristics.
Where there is a specific need to see and avoid obstacles on departure and/or for a forced landing, additional conditions, e.g. ceiling, should be specifi ed.
(2) The commander should not commence take-off unless the weather conditions at the aerodrome of departure are equal to or better than applicable minima for landing at that aerodrome unless a
weather-permissible take-off alternate aerodrome is available.
(3) When the reported meteorological visibility (VIS) is below that required for take-off and RVR is not reported, a take-off should only be commenced if the commander can determine that the visibility along the take-off runway is equal to or better than the required minimum.
(4) When no reported meteorological visibility or RVR is available, a take-off should only be commenced if the commander can determine that the visibility along the take-off runway is equal to or better than the required minimum.
(b) Visual reference
(1) The take-off minima should be selected to ensure suffi cient guidance to control the aircraft in the event of both a rejected take-off in adverse circumstances and a continued take-off after failure of the critical engine.
(2) For night operations, ground lights should be available to illuminate the runway and any obstacles.
(c) Required RVR/VIS – aeroplanes
(1) For multi-engined aeroplanes, with performance such that in the event of a critical engine failure at any point during take-off the aeroplane can either stop or continue the take-off to a height of 1 500 ft above the aerodrome while clearing obstacles by the required margins, the take-off
minima specifi ed by the operator should be expressed as RVR/CMV (converted meteorological visibility) values not lower than those specifi ed in Table 1.A.

Day only: Nil** 500
Day: at least runway edge lights or runway centreline markings
Night: at least runway edge lights and runway end lights or runway centreline lights and runway end lights 400

(2) For multi-engined aeroplanes without the performance to comply with the conditions in (c)(1) in the event of a critical engine failure, there may be a need to re-land immediately and to see and avoid obstacles in the take-off area. Such aeroplanes may be operated to the following take-off
minima provided they are able to comply with the applicable obstacle clearance criteria, assuming engine failure at the height specifi ed. The take-off minima specifi ed by the operator should be based upon the height from which the one-engine-inoperative (OEI) net take-off fl ight path can be
constructed. The RVR minima used should not be lower than either of the values specifi ed in Table 1.A or Table 2.A.
(3) When RVR or meteorological visibility is not available, the commander should not commence takeoff unless he/she can determine that the actual conditions satisfy the applicable take-off minima.