Yes; why have it and not have it available?
Why was it made INOP? That is a) dumb and b) does not comply with the STC because that stipulates a test procedure. So the aircraft was unairworthy that whole time 
Also the system should be leak checked, so on the first run you want the wingtips, belly panels, etc, removed, so you can check, as far as possible, there are no internal leaks. Those would be a corrosion disaster.
Peter wrote:
I am wondering whether washing the plane with water and then, within next few days or weeks, flying in < 0C temperatures causes the holes to fill up with ice, which the TKS fluid can’t push out.
That may be relevant. I flew last week (SR22 FIKI) and wet the wings before a descent through cloud in OAT below 0C. The TKS flow was quick and uniform across all panels that are visible.
The aircraft was then parked outside for 2 days of non-stop rain at Blackpool. Departed Blackpool in clear weather, flew back at FL110, OAT around M12. A cold front was over SE England and it was again necessary to use TKS before entering icing conditions on the arrival. Only this time, only a small section of the left wing received fluid, nothing on the right, followed by the “ANTI ICE PSI” caution. I left the TKS running on HIGH, the caution eventually cleared, and the wings eventually wet through. The aircraft was still dripping fluid 30 minutes after brakes on!
MarkW wrote:
A cold front was over SE England and it was again necessary to use TKS before entering icing conditions on the arrival. Only this time, only a small section of the left wing received fluid, nothing on the right, followed by the “ANTI ICE PSI” caution.
Did you check that the TKS system was working properly during preflight? At least for the TB20, the POH says that you should.
You could do that, but it makes quite a mess on the ground.
I make a point of running the system on the first flight each month even if that flight is not in icing, taking care to get sunlight onto the wings so it shows the liquid running out all the way along both wings.
A ground run does however enable one to check the elevator and vertical stabiliser panels properly.
Peter wrote:
You could do that, but it makes quite a mess on the ground.
Well… You can choose between that and finding yourself in an awkward situation in the air.
If I go on a long mission, I but the batt switch on and prime it on the ground when doing my walk around. You should see a steady green light. I notice the prop slinger is working as it will splash some fluid (collected from bottom disc) when cranking the engine. For local stuff I just do it in flight till I see the fluid over the wing (sun light helps to identify) and my windshield gets fogged up. As a last step I use the spray bar to clear the windshield….You should try to do this process with the sun in your back to be able to see something outside…If its hazy outside your in virtual IMC for a couple of minutes when flying into the sun….The first time I did this in perfect VFR weather it got me by surprise…:-). After a TKS flight the systems will keep on dripping from gravity for quite a while. As I have a V tail this is very noticeable on the tail side. I request every annual anticorrosion ACF50 or corrosion X specially on the tail cone…
Airborne_Again wrote:
Well… You can choose between that and finding yourself in an awkward situation in the air.
The other consideration is that TKS fluid becomes acidic over time, whether it’s in a tank in the aircraft or in the container on a shelf.
Therefore it makes sense to minimise use of the system, for example in the summer run it every couple of weeks or once per month, but only if you have the opportunity to thoroughly wash the aircraft afterwards because you’re effectively covering your aircraft in acidic fluid. Over on Beechtalk there is a thread discussing this, with some people measuring the Ph level of the fluid in their tanks. The results are quite interesting and correlate to corrosion issues on some TKS equipped aircraft.
Apparently deicing fluid is a major headache in airliner maintenance too, where the aircraft are sometimes doused with the stuff before departure.
Yes; why have it and not have it available?
Why was it made INOP? That is a) dumb and b) does not comply with the STC because that stipulates a test procedure. So the aircraft was unairworthy that whole time
Also the system should be leak checked, so on the first run you want the wingtips, belly panels, etc, removed, so you can check, as far as possible, there are no internal leaks. Those would be a corrosion disaster. Quote
I dont have too many answers.
What I understand is that the TKS was used as a part of an airframe/wing repair.
My last intel says it has never been used.
Very interesting indeed, and hard to decide if it makes sense to try to bring the system back to life or not.
Airborne_Again wrote:
Did you check that the TKS system was working properly during preflight?
No, on the basis that 1 USG of TKS had been put through the system without any problem 2 days before.
There is a POH section for testing the FIKI system that involves priming and spraying the windshield nozzles. It’s messy, but as you say better than discovering it doesn’t work when you actually need it. And a ground run allows you to check the horizontal and vertical stabilisers are wetting out, which is not possible to see in flight.
