Calculating RVRs

[allaboard]

At the flight planning stage is it legal under JAR rules to take forecast visibility from the "TAF "and convert it to an RVR to be used in calculating an approach minima at the destination or alternate etc using the DAY/NIGHT/FULL/LIMITED LIGHTS factors(x2, x1.5,x1.0)?

Understand that you can only factor "REPORTED" met vis for a CAT1 approach not CAT2 nor CAT3. I would think that "reported" means METAR or ATC declared visibility and not forecast visibility from the TAF. Searched through JAR but cant find a definition of "reported".

Can anyone help?

[Empty Cruise]

Hi allaboard,

Well, look at what TAF stands for (especially the ...Forecast part) and you will have your answer.

A report is something observed (measurement) - a forecast is more or less in the divination business.

Otherwise, you might embark on a flight JFK to LHR with AMS as alternate. You are Cat III capable, so required forecast for LHR (assuming nighttime arrival) is 100 m. (x 2,0 = 200 m = OK Cat III), and AMS, your only alternate needs only forecast 300 m. (x 2,0 = 600 m = OK Cat I). :hmm: - does not sound like a way to achieve a long and happy career, now does it? :D

Brgds from
Empty :)

[Tinstaafl]

A forecast is not a report therefore doesn't meet the 'report' requirements you mention.

Oh the hand, a report can also be a forecast eg a Metar with a statement of trend attached.

[LYKA]

Since RVR is never reported in the TAF or forecast in both the TAF and TREND it is ok to us this method - infact a number of operators do already - with limitations that it can't be used to determine T/O minimums, CAT2 & 3 minmia Circling or when an RVR is reported.

Empty CRZ: That's not how it works! If you are planning a CAT3 approach you must use the Vis i.e 200M for CAT3A - so in the case you give you would need 2 alternates! As you say AMS is a CAT3 airport , so depending on the RWY you are planning to use you would need CAT 1 minmima which would allow you to use the conversion or vis if you wish.

[Empty Cruise]

@ LYKA,

Yeah - that was rather the point :D - that is not the way it works!

Re. yours statement that it's OK to use this method... well, sitting with 2 different airline OM's in front of me + JAR-OPS 1, and all 3 agree on the term ...converting observed visibilty to RVR... So I fail to see how the VIZ metioned in a forecast (TREND or TAF) may be multiplied by the OPS1-factors to achieve an RVR in the planning stage. :(

Hope that no airlines use that procedure, as it is in direct disagreement with OPS1 (unless, of course, the local authorities have been allowed to grant an exemption) ;)

Brgds from
Empty