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Old 30th Mar 2011, 10:49
  #49 (permalink)  
patienceboy
 
Join Date: Nov 2008
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Another attempt at obfuscation. What you are referring to is a rule about whether a forecast is required for a flight, which is a totally different thing to whether an alternate is required for a particular destination.
The point of this is not to quibble, but to show that remote VFR flights hopping between strips are not unfairly disadvantaged by the alternate requirements – as was your assertion.

When questioned on an ARFORs suitability for determining meteorological minima (specifically wind) you said:

For an aircraft's crosswind or downwind limits to be exceeded - on a sustained basis - there has to be some suitable meteorological phenomena in the area (or nearby). Examples of such phenomena include cyclones, tropical lows and fronts.

If any of those are present, the ARFOR will mention it - along with enough specifics of associated wind direction and speed to make possible the assessment of alternate requirements.
I don’t agree that the ARFOR is accurate enough to comply with the requirements of ENR 57.2. As I mentioned earlier, 57.2 continually refers to “weather at the destination”, not “weather within x hundred miles of the destination”.

The winds forecast are an average for a very large area and are winds aloft – not surface winds. Local geography alone can cause winds at a specific location to be wildly different from those on the area forecast. For a light aircraft with a maximum crosswind component of 15kt, it hardly takes a cyclone to require an alternate!

The AIP also includes the words “Note: wind gusts must be considered”. Limits do not have to be exceeded on a "sustained basis". The ARFOR doesn’t give you this information. If the wind forecast at 3000ft was an easterly at 35kt, and your destination runs North/South – what will be the wind on the ground and do you need an alternate? Also refer to the ARFOR I posted earlier with a similar question re visibility.
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