OK, here goes as I understand it (sorry about the long post):
BTW, this is per our de-icing manual. Maybe different for others.
"DO NOT dispatch or takeoff in conditions of moderate or heavy freezing rain,
heavy freezing drizzle, moderate and heavy ice pellets (or when light ice
pellets are mixed with any other precipitation), snow pellets, hail, or other
icing conditions for which no holdover time exists.
END"
HOWEVER, if the LIGHT ice pellets (no listed hold over times) are the
only precip, you can go provided you do Type I followed by Type IV, and takeoff within 25 minutes from the START time. If you can't, you HAVE to go back, and do it again.
If there is other precip with the light pellets (snow, freezing rain,etc...) you can NOT do this. NO GO.
As far as the other precip (with NO hold over time), you can't go.
IF your precip conditions end up with a hold over time, you go with that.
IF your hold over time is EXCEEDED, you can do a "Pre-Takeoff Contamination Inspection" (visual) from the flight deck, or if not sure, the cabin. Then IF everything LOOKS good, you have 5 minutes to takeoff.
If not, or not sure, one can have an external check (our manual doesn't say visual or tactile), and if the "qualified person" says it looks "clean", you have 5minutes. If not, de-ice again.
Now, another qusetion: Why can't one be dispatched TO an airport with the above precip? We sat in DTW for a LOOOOONG time (where the sun finally came out) because the dispatcher said he could not "dispatch" because of the WX (not the 1,2,3 rule, but because of the precip). I thought that the "dispatch" only was for TAKEOFF???
It's hard to believe, but I may be mistaken.
