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Can TAF's visibility replace RVR?

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Can TAF's visibility replace RVR?

Old 16th Jun 2020, 21:47
  #21 (permalink)  
 
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Originally Posted by Don Coyote View Post
True, but given that it is reported met visibility it is unlikely to be of value for when you arrive two hours later in the example given by the OP. The only time it would possibly be applicable for planning minima, IAW CAT.OP.MPA.185, is when the reported met visibility is given to you before you depart and you will arrive in one hour or less.
The OP is referring to a forecasted Vis, part of a TAF. This Visibility will be taken into account as we have no further details (TEMPO, BECMG, etc..) so we can assume it is the forecasted general visibility in the period covered by the TAF.
Worst case scenario Your CMV factor is 1.0, You’re above the required RVR of 550m.
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Old 17th Jun 2020, 06:15
  #22 (permalink)  
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Originally Posted by exfocx View Post
Been back "home" (Oz) for some time now, but if my memory serves me right when in the M.E. we had a correction factor to go from Vis to RVR if only one was stated and you needed the other, factor was 1.5. When I was in HK I'm pretty sure that the company had a nominated destination VIS requirement, not given as an RVR.

Also, are not Vis and RVR different?

Edit: can see some have covered this.


3. Calculation of visibility

Visibility values are determined by both human observers and the Automated Surface Observing Systems (ASOS). The human observer determines visibility by identifying objects and landmarks at known distances throughout a 360 degree circle around the observation point. The greatest visibility observed over 50% or more of the 360 degree area is the prevailing visibility. If, however, there’s a sector of the 360 degree area that significantly differs from prevailing visibility, the observer may add a remark. ASOS measures and converts sensor-driven values to visibility values corresponding to what the human eye can see. Pilots must be mindful that nearly half the area around an airport may have lower conditions than the reported prevailing visibility.

5. RVR considerations

RVR is distance over which a pilot of an aircraft, on the centerline of a runway, can see delineated runway surface markings and centerline. RVR values are normally determined by the human eye or with an Instrumented Runway Visual range (IRVR) trasmissometer. RVR is important as it provides the main criteria used to determine category of visual aids operational at an airport as well as criteria/minima for instrument approaches.

Thank you for your reply.

Comparing the definition of VIS with the definition of RVR, I can see sure that the two are different.

By the way, your said "home (Oz)" means, you were in AAR in korea?

Nice to meet you.

And thank you very much for your help.
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Old 17th Jun 2020, 06:44
  #23 (permalink)  
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Originally Posted by Don Coyote View Post
You may be considering when you have a legal TAF but a METAR below minimums as you are very unlikely to get RVR in a TAF. For planning purposes, you would use the TAF to determine dispatch requirements.

For EASA land CAT operations, the following would be applicable:

The table in GM1 CAT.OP.MPA.185 has useful guidance for applying TAF criteria to determine suitability of weather from a TAF. Once you have determined that the forecast is suitable (or not) then CAT.OP.MPA.185 would also require alternate weather of better than NPA RVR/VIS with ceiling at or above MDH for the most applicable runway as only CAT I is available at destination. Provided those conditions are met then you could dispatch with one alternate.

If the destination forecast is below limits, as per yunje’s example of RKSI/ICN TAF of 600m visibility (800m visibility required), then you would require two alternates with suitable weather forecasts as per CAT.OP.MPA.185.

Once you arrive at the destination then CAT.OP.MPA.305 becomes applicable. This requires that you cannot proceed below 1000 ft above the aerodrome if the reported RVR/VIS is less than the applicable minimum.

The conversion of reported met vis to RVR, detailed in AMC10 CAT.OP.MPA.110, would not be applicable at the planning stage.
Thank you for your reply.

Actually, I'm considering when I have a TAF with forecasted visibility 600m. (not METAR)
But when the airport weather minimum is 'VIS 800m or RVR 550m', I'm thinking about which one to compare with TAF.

I think, you want to said,
I have to compare 'TAF of 600m visibility' with 'airport minimum VIS 800m' (not RVR 550m)
and I need to have two alternates airport in this example.
(you said : If the destination forecast is below limits, as per yunje’s example of RKSI/ICN TAF of 600m visibility (800m visibility required)...)

Is this right?

Anyway, thank you again.
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Old 17th Jun 2020, 09:08
  #24 (permalink)  

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In your original example, the VIS was greater than the RVR planning minima.

The agreement hereabove is, it is legal to dispatch. Correct? Multiplication factors not required.
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Old 17th Jun 2020, 13:10
  #25 (permalink)  
 
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Originally Posted by yunje View Post
- TAF Forecast visibility : 600m
- AIRPORT appraoch minimum : CAT 1 / VIS 800m (or RVR 550m)

Is it possible to dispatch in this case? (with one alternate airport)

It is not clear in my company regulation.
and I just wonder what ICAO/FAA/EASA ruels and others aviation workers opinion.
KingAir1978 was basically correct early in the thread.

In Europe, if the wx is below minima at destination two alternates are required (in general that is, not necessarily applicable to all operators). In the USA dispatch would be permitted with one alternate.

ICAO Annex 6 Pt 1 states that 2 alternates are required if the weather forecast is below minimums at destination. Not necessarily implemented in each country. EASA requires 2 alternates. The FAA is 1 alternate unless the weather at the alternate is "marginal" when two are required. EASA reference is CAT.OP.MPA.185. FAA reference is 14CFR 121.619 and 621.

Soncibum says:

Worst case scenario Your CMV factor is 1.0, You’re above the required RVR of 550m.
Maybe, but in Europe it is not permitted to convert the met visibility to RVR when the RVR minimum is less than 800m according to CAT.OP.MPA.110 AMC10. The implications of this rule could be discussed at length but as far as answering the OP is concerned it is a moot point because in his company:

* RVR Conversion Table Note
2. This table may not be used for landing minima determinations on Flight Planning Stage.
Furthermore...

- AIRPORT appraoch minimum : CAT 1 / VIS 800m (or RVR 550m)...
...[if] TAF visibility 600m is above appraoch minima's RVR 550m
so there is no problem, dispatch with 1 alternate
...these two things imply to me that the OP needs 2 alternates for dispatch because the forecast visibility is below the quoted Cat 1 vis of 800m and it is not permitted to convert it to equivalent RVR for the purposes of dispatch planning.
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Old 17th Jun 2020, 13:27
  #26 (permalink)  

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oggers thanks for assembling the pieces back together.

It transpires then, that any LVP CAT II/III alternate cannot be planned for, unless their forecasted VIS is 800 or more. EASA land.

​​

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Old 17th Jun 2020, 16:34
  #27 (permalink)  
 
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Originally Posted by oggers View Post

Soncibum says:



Maybe, but in Europe it is not permitted to convert the met visibility to RVR when the RVR minimum is less than 800m according to CAT.OP.MPA.110 AMC10. The implications of this rule could be discussed at length but as far as answering the OP is concerned it is a moot point because in his company:



Furthermore...



...these two things imply to me that the OP needs 2 alternates for dispatch because the forecast visibility is below the quoted Cat 1 vis of 800m and it is not permitted to convert it to equivalent RVR for the purposes of dispatch planning.
oggers,

(a) A conversion from meteorological visibility to RVR/CMV should not be used:
(1) when reported RVR is available;
(2) for calculating take-off minima; and
(3) for any RVR minima less than 800 m.

point 3) in intended after a conversion i.e. with a Vis of 400 m and a conversion factor of 2.0 you would get a CMV of 800m, but with, let's say a min RVR of 550 you could not do the conversion with a Visibility of, let's say 300m.
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Old 17th Jun 2020, 21:29
  #28 (permalink)  
 
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Originally Posted by sonicbum View Post
oggers,

(a) A conversion from meteorological visibility to RVR/CMV should not be used:
(1) when reported RVR is available;
(2) for calculating take-off minima; and
(3) for any RVR minima less than 800 m.

point 3) in intended after a conversion i.e. with a Vis of 400 m and a conversion factor of 2.0 you would get a CMV of 800m, but with, let's say a min RVR of 550 you could not do the conversion with a Visibility of, let's say 300m.
SonicBum (nice nickname!), In EASA land when you're at the planning stage, you cannot apply the conversion, because of point (3), when you're in flight and the visibility drops below 800m and you want to shoot an ILS approach, RVR should be provided. Therefore point (1) prohibits you from doing the conversion.

Last edited by KingAir1978; 19th Jun 2020 at 16:15.
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Old 18th Jun 2020, 06:11
  #29 (permalink)  

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For reference only, EASA starting point is CAT.OP.MPA.185 Planning minima for IFR flights — aeroplanes. Then it follows to CAT.OP.MPA.110.

If, A conversion from meteorological visibility to RVR/CMV should not be used .... for any RVR minima less than 800 m. [AMC 10 (a)(3)]
and by definition any TAF will only have VIS
then anywhere CAT I is required, RVR 550 must be disregarded and VIS 800 used.

That's different from sonic's suggestion. Thoughts?
point 3) in intended after a conversion i.e. with a Vis of 400 m and a conversion factor of 2.0 you would get a CMV of 800m, but with, let's say a min RVR of 550 you could not do the conversion with a Visibility of, let's say 300m.
this leaves me perplexed.
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Old 18th Jun 2020, 09:43
  #30 (permalink)  
 
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Originally Posted by KingAir1978 View Post
SonicBum (nice nickname!), In EASA land when you're at the planning stage, you cannot apply the conversion, because of point (3), when you're in flight and the visibility drops below 800m and you want to shoot an ILS approach, RVR is required. Therefore point (1) prohibits you from doing the conversion.
Hi King,

guess I have spent too much time in the SIM and not enough on the line in the past couple of years.
Here is an answer I gave to a similar question a couple of years ago.

Originally Posted by sonicbum View Post
Yes, the RVR is controlling.


At dispatch You will only have the forecasted visibility issued by the TAF. In Your example a RVR reading is available at destination so You are not allowed to use the conversion of reported meteorological visibility to RVR, hence if forecast vis +/- 1 hour is less than the required one for the approach You are considered below minima and need 2 suitable alternates to dispatch (EASA land).
in THIS thread.
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Old 18th Jun 2020, 16:27
  #31 (permalink)  
 
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Originally Posted by FlightDetent View Post
For reference only, EASA starting point is CAT.OP.MPA.185 Planning minima for IFR flights — aeroplanes. Then it follows to CAT.OP.MPA.110.

If, A conversion from meteorological visibility to RVR/CMV should not be used .... for any RVR minima less than 800 m. [AMC 10 (a)(3)]
and by definition any TAF will only have VIS
then anywhere CAT I is required, RVR 550 must be disregarded and VIS 800 used.

That's different from sonic's suggestion. Thoughts?
this leaves me perplexed.
The conversion factors for CMV, I believe, are 1.5 for daytime operations and 2.0 for night time operations assuming full lighting/facilities etc.
Let`s assume a CAT1 ILS at dest`n with a minimum published RVR requirement of 550m.
The way I interpret the 800 m limitation is that notwithstanding our 550 m RVR requirement we can`t `play` with an RVR below 800 m when conducting the conversion back to an equivalent met visibility.
Therefore at night: 800/2 = 400 and so the min forecast visibility in the TAF at ETA +/-1 hr is 400 m in order to dispatch with just 1 dest`n alternate.
For a daytime approach 800/1.5 = 533.3, so effectively the min met vis in the TAF at ETA +/-1 hr is 550 m (although in a TAF they forecast in 100 m increments so I guess you`d be looking for a minimum forecast vis of 600 m).
Anyway, it`s purely an opinion (and probably wrong!)
Any thoughts?
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Old 18th Jun 2020, 21:54
  #32 (permalink)  
 
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Originally Posted by Stanley Eevil View Post
The conversion factors for CMV, I believe, are 1.5 for daytime operations and 2.0 for night time operations assuming full lighting/facilities etc.
Let`s assume a CAT1 ILS at dest`n with a minimum published RVR requirement of 550m.
The way I interpret the 800 m limitation is that notwithstanding our 550 m RVR requirement we can`t `play` with an RVR below 800 m when conducting the conversion back to an equivalent met visibility.
Therefore at night: 800/2 = 400 and so the min forecast visibility in the TAF at ETA +/-1 hr is 400 m in order to dispatch with just 1 dest`n alternate.
For a daytime approach 800/1.5 = 533.3, so effectively the min met vis in the TAF at ETA +/-1 hr is 550 m (although in a TAF they forecast in 100 m increments so I guess you`d be looking for a minimum forecast vis of 600 m).
Anyway, it`s purely an opinion (and probably wrong!)
Any thoughts?
I'm not really sure what you're trying to say, Stanley.
EASA:

First of all it is possible to convert visibility to CMV/RVR, I don't think you can reverse it and convert a required RVR to visibility that should be present.

The conversion factor -in case of HI approach lights/runway lights- 1,5 day and 2.0 night.

The conversion cannot be used for:
  • Take off
  • For calculating a required RVR less than 800 m (i.e. 550 meters for a standard ILS)
  • When RVR is available.
Secondly, when the VIS drops below 800 m YOU SHOULD PROVIDED with RVR information.

Last edited by KingAir1978; 19th Jun 2020 at 16:15.
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Old 18th Jun 2020, 22:45
  #33 (permalink)  

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Although it is a full circle from the OP's question, here's a familiar sample case. EASA rules.

Your destination WS is ok, however company preferred alternate is not looking great. TAF LIMC (MXP) V2kt 2000 BR NSC 3/1 Q1003 TEMPO 14-18 0600 FG BECMG 20-24 220/5 6000

A well equipped major hub with dual runways, CATIIIB and given the forecast it still is a respectable choice. BTW destination is CAVOK, and a non-preferred alternate is 8000 m VIS half way between DEST and LIMC.

Alternate planning minima is one grade more restrictive than what's available, i.e. for Milano CAT I ILS R550 / VIS 800.

As much as we agreed the paragraphs we're looking at do not allow conversion of TAF 600 VIS to 900 CMV, because the target minimum is R550 (less than 800) ...
... when you ran the above scenario through the flight planning system, the answer is ACCEPTABLE.

Where's the catch?
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Old 19th Jun 2020, 06:56
  #34 (permalink)  
 
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Originally Posted by KingAir1978 View Post
I'm not really sure what you're trying to say, Stanley.
EASA:

First of all it is possible to convert visibility to CMV/RVR, I don't think you can reverse it and convert a required RVR to visibility that should be present.

The conversion factor -in case of HI approach lights/runway lights- 1,5 day and 2.0 night.

The conversion cannot be used for:
  • Take off
  • For calculating a required RVR less than 800 m (i.e. 550 meters for a standard ILS)
  • When RVR is available.
Secondly, when the VIS drops below 800 m YOU HAVE TO BE PROVIDED with RVR information.
Would this mean then that if you arrive at destination, (which, let`s assume, has a published minimum CAT1 RVR of 550 m), that if the met vis on the ATIS is 700 m, but the RVR system is inoperative, that you can`t make an approach - even though the `RVR` (if it was available) is HIGHLY LIKELY to be over 1000 m?

Or, what about a single pilot CAT1, who with his `limited` available ac equipment/avionics, is forced to use a modified min EASA RVR of exactly 800 m. He would, surely, be legal because he now CAN use a CMV conversion: [700 met vis x 1.5 (day)] = 1050 m CMV!! = LEGAL!!

So, is the obvious solution for the A320 CAT1 two-pilot operation to knock out the co-pilot, fly a manual/raw approach, and become a `single pilot operation` ?


Just out of interest, I can`t see any reference to a min met visibility of 800 m for a CAT1 approach in EASA; I assume it is mentioned in ICAO?
EASA CAT1 Definition:
‘Category I (CAT I) approach operation’ means a precision instrument approach and landing using an instrument landing system (ILS), microwave landing system (MLS), GLS (ground-based augmented global navigation satellite system (GNSS/GBAS) landing system), precision approach radar (PAR) or GNSS using a satellite-based augmentation system (SBAS) with a decision height (DH) not lower than 200 ft and with a runway visual range (RVR) not less than 550 m for aeroplanes and 500 m for helicopters;

Last edited by Stanley Eevil; 19th Jun 2020 at 07:22.
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Old 19th Jun 2020, 07:17
  #35 (permalink)  
 
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Originally Posted by FlightDetent View Post
Although it is a full circle from the OP's question, here's a familiar sample case. EASA rules.

Your destination WS is ok, however company preferred alternate is not looking great. TAF LIMC (MXP) V2kt 2000 BR NSC 3/1 Q1003 TEMPO 14-18 0600 FG BECMG 20-24 220/5 6000

A well equipped major hub with dual runways, CATIIIB and given the forecast it still is a respectable choice. BTW destination is CAVOK, and a non-preferred alternate is 8000 m VIS half way between DEST and LIMC.

Alternate planning minima is one grade more restrictive than what's available, i.e. for Milano CAT I ILS R550 / VIS 800.

As much as we agreed the paragraphs we're looking at do not allow conversion of TAF 600 VIS to 900 CMV, because the target minimum is R550 (less than 800) ...
... when you ran the above scenario through the flight planning system, the answer is ACCEPTABLE.

Where's the catch?
Hi FD,

in your example, the forecasted visibility is greater than the required RVR for CAT I, hence LIDO (example of what we use in my company) will accept it and will not mark it as "U".
Regarding the conversion, you can convert 600 m of visibility. What the rule says is that you can't convert in order to find RVRs lower than 800 m. If I have a general visibility of 400 m and a conversion factor of 2.0 I will find a CMV of 800m, I'm ok. On the other hand, if I have a conversion factor of 1.5 with the same visibility (daytime, HIRLS) I will find 600 m, less than 800 m , so not allowed.
Let me know your thoughts.
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Old 19th Jun 2020, 07:20
  #36 (permalink)  
 
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Originally Posted by Stanley Eevil View Post
Would this mean then that if you arrive at destination, (which, let`s assume, has a published minimum CAT1 RVR of 550 m), that if the met vis on the ATIS is 700 m, but the RVR system is inoperative, that you can`t make an approach - even though the `RVR` (if it was available) is HIGHLY LIKELY to be over 1000 m?
No, You can by using the CMV table.

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Old 19th Jun 2020, 07:28
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Originally Posted by sonicbum View Post
No, You can by using the CMV table.
KingAir1978 would disagree with you I believe?
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Old 19th Jun 2020, 07:31
  #38 (permalink)  
 
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Originally Posted by KingAir1978 View Post
Secondly, when the VIS drops below 800 m YOU HAVE TO BE PROVIDED with RVR information.
ICAO :

4.6.3 Runway visual range

Note: Guidance on the subject of runway visual range is contained in the ICAO Manual of Runway Visual Range Observing and Reporting Practices (Doc 9328).

4.6.3.1 Runway visual range as defined in 1 above shall be assessed on all runways intended for Category II and III instrument approach and landing operations.

4.6.3.2 [Recommendation] Runway visual range as defined in 1 above should be assessed on all runways intended for use during periods of reduced visibility, including:

(a) Precision approach runways intended for Category I instrument approach and landing operations; and
(b) Runways used for take-off and having high-intensity edge lights and/or centre line lights.

Note: Precision approach runways are defined in ICAO Annex 14, Volume I, Chapter 1, under “Instrument runway”.

4.6.3.3 The runway visual range, assessed in accordance with 4.6.3.1 and 4.6.3.2 above, shall be reported in metres throughout periods when either the visibility or the runway visual range is less than 1 500 m.

4.6.3.4 Runway visual range assessments shall be representative of:
(a) The touchdown zone of the runway intended for non-precision or Category I instrument approach and landing operations; 19
(b) The touchdown zone and the mid-point of the runway intended for Category II instrument approach and landing operations; and
(c) The touchdown zone, the mid-point and stop-end of the runway intended for Category III instrument approach and landing operations.


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Old 19th Jun 2020, 07:34
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Originally Posted by sonicbum View Post
Hi FD,

in your example, the forecasted visibility is greater than the required RVR for CAT I, hence LIDO (example of what we use in my company) will accept it and will not mark it as "U".
Regarding the conversion, you can convert 600 m of visibility. What the rule says is that you can't convert in order to find RVRs lower than 800 m. If I have a general visibility of 400 m and a conversion factor of 2.0 I will find a CMV of 800m, I'm ok. On the other hand, if I have a conversion factor of 1.5 with the same visibility (daytime, HIRLS) I will find 600 m, less than 800 m , so not allowed.
Let me know your thoughts.
This is EXACTLY in accordance with my own interpretation of the rules for CMV as I posted earlier.
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Old 19th Jun 2020, 16:13
  #40 (permalink)  
 
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Originally Posted by sonicbum View Post
No, You can by using the CMV table.
Originally Posted by Stanley Eevil View Post
KingAir1978 would disagree with you I believe?
No I typed something from memory that wasn't entirely correct. Below 800m LVP should come in force, and you SHOULD be provided with RVR. I've amended my previous post.

With regards to single pilot ops... I'm not too knowledgeable about that, because it's been more than 15 years ago that I've operated single pilot. I seem to recall that you need a working autopilot or HUD if the vis/rvr falls below a certain level, but I'll leave that for others to answer.
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