Hay, not quite right re. boots, I don't think. I suspect I have a fair amount of ice experience....much in booted planes, however probably more in non-deiced planes. For those that don't know, boots are pneumatically inflatable ribs that run parallel to the leading edge of the wing. They extend about 6" over the top & the bottom of the wing. They look like a big inner tube that's been glued to the wing. You also find them on the rear flying surfaces also, like the horizontal & vertical stabilizer on the rear of the plane. There is an air pump usually on one or more of the engines of a multi-engine plane. The single PT6 turbine in the Pilatus probably had 2 air pumps to be certified for known ice, which it probably was to be of much use at all as a turboprop. When the boots are activated (blown UP), the ribs expand outward about 3/4" & break away the layer of ice that has formed on the leading edge, which is the most hazardous part to an aircraft's performance....but certainly not the entire problem w/icing. The boots stay inflated for about 10 seconds & then deflate flat again. A pilot can activate them once, or 100 times depending on conditions.

Boots are not "anti-ice" equipment, they are DE-ice equipment. Most pure jets use "hot wings" (actually just the leading edge) that have hot bleed air coming from the engines. This would be a form of anti-ice protection, just like the venerable old pitot heat. You would normally (if so indicated in manual) turn the anti-ice equipment ON before entering conditions of suspected or known icing. However, it's a wise thing to "check" boots before entering ice to know what you're working with. Actually, it's imperative to check boots before takeoff to know IF they're working. They may be a "go, no-go" item....depending. Some of the smaller jets also used boots, like the earlier Cessna Citations. Some booted planes have automatic cycling for inflation, but most of the piston twins require pilot activation of each cycle. I'm guessing that t-prop had some type of auto-cycling for the boots.

The reason you don't INflate boots before ice builds sufficiently (usually minimum of 1/2"-3/4" of buildup) is because the ice may conform to the INflated shape of the boots & when they deflate (automatically), you'll be left with ice still sticking to the boots & forming a larger leading edge than before you started. So basically, you want to let ice form before hitting the boot switch. Boots seldom clean off the ice 100%. There's always some hanging-on stragglers. If you know before take-off that you're going to be encountering heavier ice, pilots often coat the boots with a silicone spray to help avoid the ice sticking to the rubber surface. That's OK as long as you dn't encounter heavy rain before the ice which would wear away the silicone. Now, the same is NOT true with the anti-ice surfaces of the plane. Most turboprops have boots, not hot wings. The propellors on prop type (turbine or piston engine) planes are also protected in most cases by heated pads in the inner 12" or so of each blade. These you DO turn on before entering icing, and then leave them on. They have their own cycling mechanism.

Personally, only from what I've read thus far, I don't suspect icing. Coming thru a relatively thin layer of clouds in a pressurized plane (like the Pilatus) probably wouldn't have allowed much ice accumulation, even if no deice was used. Now, much of my personal thoughts (I won't share them here) have to do with the flight experience of the pilot...which I have no knowledge of. Depends on his background & flight experiences. Since over 1/2 of the pax were little kids, I'm doubting the c.g. should have caused the crash. Could be wrong though.

Whatever...it was very-very sad indeed.