TKS plumbing check

[PaulM]

Everyone that has the TKS system installed should check the amount of slack in the line to the tail divider fitting.  (available via the tail cone access panel) 

When my Bravo installation was run to full up trim the lack of slack pulled the line out of the coupling. 

A check of an Ovation in the shop had barely any slack at full up trim, obviously my system had never before been run full up, and must have been stretching that line at medium trim settings.  

Timeline:

Feb:  Ran TKS to check for full wetting.  No problem found

April:  After annual:  Stec AP tests,  ran the trim full up and full down during the test sequence, no trim motion problems. 

          TKS stall strip glue comes undone.. 3 stall strips, re-glued, none lost.   (Did not test since the glue had to set)  

May:  Tested TKS, had fluid pouring out of the tail cone only. 

Today:    Ran new line from belly fitting to tail cone with proper slack at full up trim.  All panels wetted, trim checked full up and down. 

[carusoam]

See if I can state this more simply...

Trimming the tail, tugged the plumbing apart?

 

Follow up question: where/who installed your TKS system?

Best regards,

-a-

[PaulM]

I was a little more verbose to fend of the initial set of  did you check x, y & z.

Install was at the Mooney factory @ 2.7 hours. June 2005. 

The CAV installation instructions say to leave 3% extra length for temperature variations, etc.    It does not say to install at max trim extension. 

The A&P that did the annual said that he did a full up trim check and that the tube wasn't disconnected when the inspection panels were closed up, but he did not run the system, so it could have just "looked" ok, but not sealed under pressure. 

Our quandary was why it worked fine for eleven years,  failed now, and seemed that it should have failed much earlier.  

[LANCECASPER]

The good news is that you found it on the ground and didn't have the elevator ice over in flight.

[carusoam]

Something doesn't sound quite right from an engineering point of view...

The fittings used on this type of plumbing don't usually pull off very easily.  You may want to check if they compressed properly.

reuse of some parts of compression fittings are not permissible.

I am not familiar with this particular system.  But I know industrial tubing and fittings pretty well...

post a picture if you can...

Best regards,

-a-

[PaulM]

The picture was up above..  At first we thought it had just pulled out, but when we attempted to reassemble the unit there was not enough slack in the system to allow re-connection, and at high up elevator trim the plumbing did not match up at all (pic ^^)  

Therefore a new 5/16" line was run, and the correct compression fitting swaged onto the pipe..  A well known issue with TKS installs. 

Edited May 21, 2016 by PaulM

[carusoam]

The picture doesn't show the parts of the fitting that would indicate if it was not assembled correctly.

It worked before, so I thought it had enough length.  Maybe not the proper length.  

It was installed once with the proper length.  Something has changed...

When the fitting on this type of tubing is opened for maintenance, the piece of tube gets cut off to put a new ferrule on the tube. The parts get compressed to form the seal.  Each time this is done a couple inches get trimmed off.

Sooner or later, the last mechanic gets caught holding the bag... Or can't cut it enough to make it longer.

Since the operation of this device is somewhat critical, a simple loose fitting will drain all the fluid without sending it through all the panels completely.

solution, get a mechanic that is familiar with the TKS tube and fittings.  The industrial supply catalog probably has the parts.

Other places where tube and ferrules are used is the O2 systems.  The parts come from an industrial supplier who also makes aviation stuff.  (Scott)

A third look at the photo...  looking as close as I can at the end of the tube...  The definition of the photo doesn't really show enough detail.  But, the tube looks marred as if a ferrule had been there? And a fair amount of tubing would need to be trimmed to put a new one on.

See what I am saying?

The best parts of this thread is your advice and fair warning to people with TKS systems, and the fact that you have yours fixed properly.

Is it normal maintenance that would open the fittings?  Cleaning or draining?  If it is, 3% isn't going to be enough when they trim inches off a line.

Best regards,

-a-

[PaulM]

I think that it had enough length at low trim settings, and perhaps the system was always stretching the piping at high trim.   If the tubing was ever cut/trimmed then it was before I owned the plane.   

We also looked at an Ovation with the system, and there was no slack at full up trim, it did not bind, but there was no extra margin there. 

the shop in Trenton was familiar with the system, and had the CAV installation instructions, they had the replacement tubing on hand and the proper swage tools, so it has been fixed.   My memo was to others to just check that they have no interference at full up trim on their systems.    

It could have been a progressive problem,  each time the trim went beyond X% the system was stressed.  after 10 years it had finally reached its limit. 

[carusoam]

Another place where Mooneys have run into a similar accidental maintenance interference issues with the tail trim...

Improper replacement of the ADF wire that ran to the top of the tail.  Under near full down trim like cruise flight. the length of ADF antenna wire can come up short and the tail is easily supported by the antenna wire. Until it breaks.

Trimming down doesn't seem to be able make a difference if the tail is being held up...

You will get a good feeling how much slop is in the tail.  The test of lifting the tail in pre-flight gives an indication.

My old C had about a 1/4".  My O is nearly imperceptible. It is easy to swap out the tail bolt to remove the slop if you have it.

Hanging by a wire at the top not getting enough down trim...

Or hanging by a tube at the bottom not getting enough up trim... 

Both are kind of scary.  Especially, when the interference lets go during flight.

Thanks again Paul for sharing this 'interesting' situation with the TKS system.

Best regards,

-a-

[Yooper Rocketman]

That line probably WAS too short, but if the ferrule had been properly swaged, it would not have come off.  Either way, your solution was the best; new line with proper slack.  There are swaging tools for each line size and the ferrules are unique to TKS.  I have never had a line apart on any of the 3 "in service" systems I have had.

I love the system, but installs 10-15 years ago were not at the highest level.  I had the access panel fall off my Mooney on the way home and spent the first 3 years after install insulating and securing TKS lines in the wings and fuselage to prevent chafing or cutting of the lines.  The first Bonanza had the same issues.

Tom