(Paul Tomblin) wrote:
Especially since the FAA is now regarding "known icing conditions" to
mean any time when there is a mention of icing in the forecast, even
if you have pireps of no icing.

You say that like it's a bad thing. I don't think it is.

We just don't know enough about icing to be sure when or where it's
going to occur. If our best prediction methods say "there's likely to
be ice in clouds between 5000 and 12000", just because you fly into a
cloud at 8000 and don't pick up any ice doesn't mean the predicion is
any less valid.

Half an hour later, it could be half a degree colder and that could be
the difference between ice and no ice. Five minutes later, that exact
location could be in a downdraft instead of an updraft, and that could
be the difference. Maybe the conditions are such that your airspeed, or
the shape of your leading edge makes the difference. Maybe the guy
before you just took off and has warm skin while you're descending with
a cold-soaked airframe.

Let's say I told you "The flight plan shows 2.5 hours in the air and
you've got 2.6 hours of fuel on board". Would you think it safe to
attempt the flight? I assume you wouldn't. Now, if I told you some guy
just made the same flight in the same type aircraft with the same amount
of fuel when he started and got there just fine. You now have an
empirical observation that 2.6 hours of fuel is indeed sufficient.
Would this change your mind about whether it was safe to launch or not?