5th Aug 2001, 07:48
In this part of the world if you have a Metar with a "trend" added it becomes a trend type forcast (TTF). The TTF is only valid for a short period of up to 3hrs and will take priority over the Taf for that period.
When I operated in Europe we used a Metar with a "trend" as just a Metar with a further observation and not as a forecast.
My question is do other countries use a TTF as a miny forecast?
6th Aug 2001, 18:33
In Europe, the TREND forecast, which is attatched to the METAR, is valid for 2 hours, and overrules the TAF in the period of its validity.
However, with the "new" JAA (European) rules, the weather on the destination (or alternate) airport has to be above planning minima one hour before and one hour after your ETA. Since the TREND forecast only "lasts" for 2 hours, your ETA has to be "smack in the middle" of that time period. On the second. :D
Therefore: If the TREND forecast is an improvement compared to a (below minima) TAF, you normally have to disregard it when picking one or two alternate airports and deciding on minimum fuel.
On short haul legs (say 50 minutes or less) you can always use the TREND forecast (of an updated METAR) when assessing the probability of a diversion and deciding on how much extra fuel you want to take with you.
If I fly a 30 minute leg, the METAR on the destination says CAVOK and the trend says NOSIG, and there is a TAF saying for example PROB30 300m FG, I will have to pick out two alternate airports, but I probably wouldn't bring as much extra holding fuel as I would if there were no TREND on the METAR. All other aspects considered, of course.