Weather Minima for Planning Purposes
 

Ladies /Gents,

When calculating whether your destination and alternate airfields are within limits, should you (by the letter of the law) take into account any tempo groups in that airfields TAFS ? If so how about prob 30 or prob 40 tempo groups ? :confused:

I have searched high and low for the answer and whilst the requirements as laid down in JAROPS 3 with regard to weather minima is clear, it doesn't mention the above.

I have had opposing opinions stated by two Captains and would be most grateful if anyone could point me in the direction of the definitive answer ?

Many Thanks

I think you'll find a lot of SOPs say ignore Prob 30 or below. Of course, depending on your experiences with met forecasting, ..........................

It should be in your OPS manual???

Thank you for your reply BOAC.
Unfortunately our Ops Manual gives no guidance other than to say that the weather at home plate and alternate must be within limits. As it stands I am applying all the tempo and prob groupings to cover my six, however it is having a detrimental affect on what I can and cannot do.
Notwithstanding the above, I am not for a moment advocating that I should ignore TAFS (I could not legally) and I have a healthy respect for the weather and would always aim to be safe rather than sorry. However flying a helicopter as I do, it is often frustrating when a very pessimistic prob 30 grouping in a TAF, hamstrings my efforts, especially when I can look at the local weather and see that it isn't perhaps as bad as the TAF is predicting.

A Helicopeter:) Well, unless you are flying IFR/airways (when you are in the same position as fixed-wing), from the small amount of choppering I have done I might be tempted to 'ignore' (ie pay less regard to) Probs anything, since you have so much more flexibilty to manoeuvre/slow down/put down if things go bad - but I have not 'choppered' as a job, so not good advice!

From my Ops Manual (ICAO Annex 3 is the reference);

With respect to TEMPO (alone), TEMPO FM, TEMPO TL, TEMPO FM...TL, PROB 30/40 (ALONE);

Any deterioration in TRANSIENT/ SHOWERY conditions are not applicable for Destination, T/O Alternate, Destination Alternate or Enroute Alternate for ETA +/-1hr. Mean wind and gusts exceeding required limits may be disregarded.

However, PERSISTENT COINDITIONS are appicable and mean wind should be within required limits ut gusts may be disregarded.

ANY improvements, in any case, should be disregarded.

With a PROB TEMPO, deterioration may be disregarded: improvement should be disregarded, including mean winds and gusts.

The above is NON-ETOPS.

Hope this helps.

PP