I operate under the assumption that the system could fail at any point. If the TKS stops working, I always make sure I can make somewhere with a decent approach.
That being said, my wings and tail were 100% ice free the whole night. I felt bad for exactly 18 seconds about how much 9 gallons of TKS cost the company but other than that, flawless.
Wow that long. 18 seconds is a long time to feel guilty IMHO. I have gotten ice on a 172 before, but I had many, many outs. Namley 0'msl below me. I knew it was there, and I knew sea level was @ 12c. What I didn't figure on was the rising air along the mountsins that climb to '6k, then a small valley and back up to almost 9k at it's highest. Freezing level was at 6K acording to forcast. We started flying through soupy snow. leveled off and asked for lower. We finally got out of it at about 3100'. And it was already melting off rather quickly. MVA where we were was 2800 I think. It was just enough to turn the leading edge of the tire milky. I had seen trace before, but not the same as this. All I had ever gotten prior was from clouds mostly. This was from precip. I would estimate no more that 1/8 to 1/4 of rime at the thickest point. Still just trace amounts. But it was enough quick enough to take notice. That airplane had issue's with carb ice that flight as well. Needless to say, it tought me a few lesson's.
#1: Forcast are not always accuracte, and terrian effect's temps more than I could have imagined.
#2: If it changes from wet to frozen, in any airplane if your not ready for it, it can come on quicker that you think. So when it does, DO SOMETHING. Not now,
but right now. Take immiediate action. Don't wait and make sure your airplane can handle what you are going to do to it.
#3: See #1 again please. It still could be more than your airplane can handle. So you had better have an out planned before you even go.
I have never been in a situation where I had to worry about ice with an airplane certified for FIKI. So I have no real experince of flying real iceing. I hope when I do, I
never have to test it to it's limits.