Initial part of the TAF applicability for planning

[giggitygiggity]

I've been studiously reading up on planning minima and not sure if I understand it correctly. We've got this little chart that tells you whether or not an aerodrome is suitable for planning purposes (attached).

Say a TAF looks something like this (I made it up, but you get the idea):

EGKK 160500Z 1605/1705 01007KT 0050 FG OVC001 BECMG 1608/1610 CAVOK


If our flight was planned to land at 1200Z then obviously, in reality we'd expect it to be CAVOK. However looking into the planning applicability, can we consider this to be suitable or would we need a second alternate as the planning table says...

"The prevailing weather conditions forecast in the initial part of the TAF should be fully applied with the exception of the mean wind and gusts (and crosswind) which should be applied in accordance with..... "

Therefore is the FOG/Low Vis on the example forecast valid for the whole 24 hour period of the TAF to suit the planning rules?

To confuse things even further, the same table also says that
The Time period is valid from the start of the TAF validity up to the time of applicability of the first subsequent FM or BECMG, if no FM or BECMG is given, up to the end of the TAF validity period

So does that mean that the BECMG cancels out the Low Vis entirely from the planning stage?


I realise there is a difference between looking for the TAF for advice as opposed to interpreting it for flight planning, but I just want to clarify this as it seems pretty confusing.

The original planning table is attached for reference.

[B737900er]

I would say for planning purposes the weather would be expected to improve within the +/- 1 hour window required so it will be suitable. Now, my airmanship would take this with a pinch of salt.

The BECMG cancels out the the LVP's yes.

[RTN11]

Spot on, from a legal stand point you can use it as a destination with one alternate, or use it as a destination alternate, but from a practical point of view you would take as much fuel as you can and have at least two decent alternates in the back of your head.

[giggitygiggity]

I realise the weather is perfectly suitable and the fog should have cleared by 1000z in my example, I'm just asking specifically if you must legally declare two alternates in this instance.

Of course, it's only a forecast and you take it with a pinch of salt. Fog especially has a tendancy to stick around longer than the boys and girls in Exeter guess, and of course if this were a real scenario, I'd take a suitable amount of fuel. I'm just asking legally where you stand.

But why is the phrase "The prevailing weather conditions forecast in the initial part of the TAF should be fully applied" in a TAF if that's never the case. If there wasn't a BECMG/FM, the phrase would be irrelevent anyway, so why have they included it?

I don't meant to be obtuse and realise my question is entirely academic but I just don't understand the required criteria specifically laid out for flight plans.

[RTN11]

OK, so in the table it says +/- 1 hour in the left column, and for improvement to take the application of improvement on a BECMG from the end of the applicable change.

So in your example TAF, it is legal to use as a destination with one alternate, or to use as a destination alternate from 1100z.

A) is the bit which states the validity is taken up to the first BECMG.

B) is badly worded, what it's actually saying is that you don't have to apply the wind if it is overridden by a PROB or TEMPO, but the prevailing weather beyond any PROB or TEMPO should be applied up to the first BECMG.

You're taking the word fully in B to mean for the entire time period of the TAF, when actually the whole sentence is saying apply everything apart from the wind if the wind is amended by a BECMG AT, PROB or TEMPO.

[B737900er]

The reality is, you will read the TAF and make a mental picture of what is going on then decide if you like it or not. If you do not like you would just uplift extra fuel or plan alternatives.

[wiggy]

It’s wot RTN said...

The wind is the only bit of your example TAF that is “fully applied” throughout the forecast period because that is the only element of the forecast that is not modified by the BECMG statement.

Or in other words, using B737900er idea of a mental picture, your TAF of:

1605/1705 01007KT 0050 FG OVC001 BECMG 1608/1610 CAVOK

Can be translated as throughout the period of the forecast (from 0500UTC to 0500 UTC) the wind will be 010 at 7 Knots. There is forecast to be dense fog and low cloud initially with but by no later than 1000 UTC it will be CAVOK.

From a legal POV (and in accordance with your table) you can plan on the basis of it being CAVOK from 1100 UTC onwards.

[giggitygiggity]

I'm sure you're all bored of me by now although I'm still not convinced. Breaking that very poorly written sentence down...


The prevailing weather conditions forecast in the initial part of the TAF...Referring to the weather at the beginning of the TAF, in this instance, the 50m visibility, the Fog and the 010/7kts of wind.


...should be fully applied... Applied to the whole period of the forecast, it can't mean anything else.


...with the exception of the mean wind and gusts (and crosswind)...Meaning that rule does not refer to the wind conditions forecast at the beginning of the TAF - so in my example, just the low visibility and the Fog are the only relevant parts at the beginning of the TAF.


...which should be applied in accordance with the policy in the column “BECMG AT” and “FM….” in the table on the next page. ... Meaning that ONLY the wind conditions should be applied with the policy of +/- 1hr given later on in the tables left column.


... This may, however, be overruled temporarily by a “TEMPO” or “PROB” if applicable, according to the table on the next page.Meaning TEMPO or a PROB overrules the 'full application' of 'initial part of the forecast'. If that is the case, any condition regarded as an Improvement given in a TEMPO or a PROB 'Should be disregarded' anyway in accordance with the second from right column. So if it were to say TEMPO 10-12 CAVOK, it's not relevant.



Again, I know this is entirely academic and you'd take fuel accordingly. I am just trying to understand what the table says. I know how to interpret a TAF and I am not being disingenuous as to your responses. This table is not there to advise you on how much extra fuel you should take, your experience is there to tell you that, it's to legally define when an aerodrome is considered suitable and above planning minima - therefore one which you can declare on your flight plan before it gets sent off to Brussels.

In my interpretation, I think what they're getting at is that if there is currently a 'persistant condition' such as FOG, DUST or rain, they are covering themselves in case it lingers for a longer period. Wind on the other hand is slightly more predictable and can be forecast with a little more precision - so that confusing statement is allowing you to disregard it. They are just warning you that the airfield might not be therefore suitable for planning purposes so a second alternate might be required.

[RTN11]

You are completely misinterpreting the table.

1 states how to apply the initial part of the TAF, under which A states the initial TAF is only valid up to the first BECMG or similar, and B states that everything apart from the wind should be applied in full, as the gusts can be disregarded for planning purposes as per 2.

Section 2 then states how to apply the rest of the TAF, and clearly states that for all cases improvement shown by a BECMG is applicable from the end of the change. Therefore, for +/- one hour, in the example TAF you have given, for planning purposes the field can be taken as CAVOK from 1100z.

Many places issue 24 hour TAFs, what use would these be if there is fog in only the first two hours, and that has to be applied as planning minima for the entire period of the TAF?

This table is only designed as a quick reference. If you go to EASA ops and look at the acceptable means of compliance, it spells it out quite clearly:

AMC1 NCO.OP.160 Meteorological conditions

APPLICATION OF AERODROME FORECASTS (TAF & TREND) — AEROPLANES AND HELICOPTERS
Where a terminal area forecast (TAF) or meteorological aerodrome or aeronautical report (METAR)
with landing forecast (TREND) is used as forecast, the following criteria should be used:

(a) From the start of a TAF validity period up to the time of applicability of the first subsequent
'FM...' or 'BECMG' or, if no 'FM' or ‘BECMG' is given, up to the end of the validity period of the
TAF, the prevailing weather conditions forecast in the initial part of the TAF should be applied.

(b) From the time of observation of a METAR up to the time of applicability of the first subsequent
'FM...' or 'BECMG' or, if no 'FM' or ‘BECMG' is given, up to the end of the validity period of the
TREND, the prevailing weather conditions forecast in the METAR should be applied.

(c) Following FM (alone) or BECMG AT, any specified change should be applied from the time of the
change.

(d) Following BECMG (alone), BECMG FM, BECMG TL, BECMG FM TL:

(1) in the case of deterioration, any specified change should be applied from the start of the
change; and

(2) in the case of improvement, any specified change should be applied from the end of the
change.

(e) In a period indicated by TEMPO (alone), TEMPO FM, TEMPO TL, TEMPO FM TL, PROB30/40
(alone):

(1) deteriorations associated with persistent conditions in connection with e.g. haze, mist,
fog, dust/sandstorm, continuous precipitation should be applied;
Regulation (EU) 965/2012 on air operations Annex VII – Part-NCO
NCO.OP

(2) deteriorations associated with transient/showery conditions in connection with shortlived
weather phenomena, e.g. thunderstorms, showers may be ignored; and

(3) improvements should in all cases be disregarded.

(f) In a period indicated by PROB30/40 TEMPO:

(1) deteriorations may be disregarded; and

(2) improvements should be disregarded.

Note: Abbreviations used in the context of this AMC are as follows:
FM: from
BECMG: becoming
AT: at
TL: till
TEMPO: temporarily
PROB: probability

[oggers]

giggitygiggity, I don't think you should "interpret what they are getting at". There is no point in second guessing your ops manual. If it is not clear to you then you should seek clarification from management.

Personally I don't see a problem. The conditions in the TAF apply during the time group of the TAF or as modified by the change indicator (BECMG etc). BECMG 0810 CAVOK means the forecast is officially CAVOK after 10Z. For the purposes of alternate planning, if your ETA is more than 1 hour after that, you may plan on CAVOK at destination.

As for the wind, the mean wind forecast is the wind for planning purposes whilst gusts can be can be disregarded.

[Ascnt1]

We can use it as alt or dest from 11:00z because of arrival at 12:00z - 1hr = 11:00z, correct?