"David Megginson" wrote in message
. cable.rogers.com...
Mike Rapoport wrote:

There is no doubt that forecast icing is known icing to the FAA and the
NTSB. This has been beat to death many times here and in every aviation
publication.

The problem is (as always) the edge cases:

1. If icing is forecast at 15,000 ft, is flight at 3,000 ft considered a
flight into known icing? What about a flight at 14,000 ft?


Ice is forecast in clouds and precipitation from the freezing level to some
altitude. If you are below the freezing level then you are not in the area
forecast for iciing. This is not an "edge case", the icing is forecast only
at certain altitudes, the area outside of those altitudes has no forecast
for icing.

2. The U.S. Current Icing Potential is a percentage, not a boolean. Is a
current icing potential of 10% equivalent to known icing? What about 25%?


Known icing is the area, altitudes and conditions in airmet Zulu. You have
to be within the described area, AND in the described conditions (cloud or
precip), AND between the freezing level and the upper altitude limit. Ice
is not forecast (or possible) if any of the three conditions are not met.

3. Is VFR flight under a blue sky considered a flight into known icing
when
a high probability of icing was forecast at that altitude in that area?

As above the icing is forecast in clouds and precipitiation. It is not
forecast in clear air. It is imposible in clear air.

What about VFR under a high overcast with good visibility and no visible
precipitation?

This is probably subject to interpretation.

Mike
MU-2


All the best,


David