It is comforting that my TKS-fellows also had their sweat moments.
Boots are nice and good but with experience I am really not willing to fly (up or down) through more than 3000 ft of icing layer with my “FIKI” setup.
3000 ft is 3 minutes on the way up and 2 on the way down and this is all I am prepared to stay in “pick up ice mode”.
Consequence: staying home this week end. There is a 10’000 ft icing layer – no go
I have some experience in different levels of icing in TB20 and DA42 both with full airframe and propeller(s) TKS. Almost every time the icing was worse than forecasted. I’ve found severe icing at -24, I’ve found it when not forecasted at all. TKS on, alternate air on and closely watching accumulation, monitoring the engines, monitoring TKS pumps and planning the escape route are the actions that I immediately perform and it works. What I learned few days ago is that there could be huge difference between turning TKS on prior and after hitting icing conditions. In pretty light conditions I got ice layer over leading edges which TKS fluid wasn’t able to remove i.e. it removed it just on few spots, unnecessarily spilling fluid through these spots at max rate while at the rest of the wing nothing was happening until I descended to a bit higher temperatures. On all previous encounters that haven’t been a problem.
DA42 (at least ng and newer) requires alternate air open anytime in IMC. Failures could be owners disregarding this (as I’ve witnessed firsthand). Or disregarding temp limitations when using diesel.
@Timothy did your aztec have the tip tanks? Mine has them and the drain valve isn’t at the lowest point of the tank, so water could get trapped in the tip tanks and make its way to the outboards once the plane starts moving, or at least that’s what I’m thinking.
Back in winter 2018 the airplane was sitting outside and I think that someone once confused my aircraft with a gas station, as evidenced by the high evaporation rate in 30L increments and the fact that some of the fuel caps weren’t quite close. Of course it had rained and as a result I had water in all tanks. I drained it all and I’m 100% positive that I was getting pure 100LL from the quick drains after doing so. Still, the right engine stumbled right after takeoff; after landing I drained another half liter from the right outboard tank.
My SOP is to takeoff on the inboards as a result.
The scenario where alternate air protects is AFAIK applicable only where the fuel servo ices up.
And that would not resolve itself by changing tanks.
On the TB20 layout, the alternate air (data posted at my link above) is plenty warm enough to ensure the fuel servo inlet is above 0C, with an OAT down to about -35C (IIRC).
It is not an alternate air issue otherwise it would not resolve itself when changing tanks.
I recall tales of Partenavia twins icing up on the air inlet and making a few people sweat a bit. Alternate air is provided to get over this.
A fold in the bladder tank could store some water which is not picked up in the drain of the Aztec. I suppose it could just be an issue with one tank but if I remember correctly Timothy had the starboard tank issue as well as me so unless it is something specific to the installation on that side it seems unlikely. I suppose it could just be a strange coincidence.
A few years ago there were a few instances of a dual engine failure in Beechjet400A aircraft, in the cruise in the high 30’s low 40’s.
It was dealt with by changing SOPs on Anti Ice usage local copy
I had never heard about that Aztec issue and I would love to know more. There are no limitations in the POH, even for aircraft with no ice protection whatsoever. The section about icing is actually missing from the original POH, it was added by an AD in 1999, see here local copy
I’ve flown in air below -20C a couple of times (FL190 across Canada, FL160 across the rockies) and I didn’t run into any issue (actually I did, I lost the heater at FL160 once. In shorts & t-shirt.). The only ice-related issue I had was the air filters icing up in IMC causing both engines to cough which scared me quite a bit. Personally I’m out of the “flying into icing conditions” game.
On a side note, I’m wondering how someone trains for flying in icing conditions. I got my IR without entering a single cloud so the first ice encounter was a little less that pleasant.
