Bellcrank bolt loose for stabilator control rod

[Anticept]

Just a small public service announcement: make sure you understand how your stabilator "feels" when you do your preflight. I just had an instructor come back and said the pitch control felt a little loose. Both sticks had the symptom, so I popped open the tunnel to look. The fiber lock nut holding the bolt in the rod end and bellcrank was hanging by just a couple of threads. If the bolt worked its way out, pitch control with the stick would have been lost and the pilot would have needed to fly using the trim (entirely separate mechanism).

 

BE CAREFUL OUT THERE!

 

PS: for those that are curious, the stabilator bowden cable has a rod end in the tunnel.

[Jacques]

 

on mine..I had the REAR nut came loose

 

strange feeling inded

[Doug Hereford]

Corey,

This has a Safety Directive ring to it. I would be very curious as to why the nut was so loose. In the standard airworthiness world, flight control

fasteners subject to rotation (like rod end nuts) require double safety features, like fiber lock and cotter pin.

Seems like it might be worth a follow up with Flight Design. Just a thought.

 

Doug Hereford

[FastEddieB]

Just wondering...

 

Is this relevant?

 

NTSB 830:

 

"Immediate notification.

 

The operator of any civil aircraft, or any public aircraft not operated by the Armed Forces or an intelligence agency of the United States, or any foreign aircraft shall immediately, and by the most expeditious means available, notify the nearest National Transportation Safety Board (NTSB) office1 when:

 

(a) An aircraft accident or any of the following listed serious incidents occur:

 

(1) Flight control system malfunction or failure..."

[Anticept]

It wasn't a malfunction (yet). But, I am notifying FDUSA.

[WmInce]

I wish there was an inspection port around that area.

[Doug Hereford]

Corey,

In my opinion, you had an "unsafe condition".  It does not matter that the system had not completely failed. At the very least, this most likely warrants a MDR to the FAA. Of course, as a part 91 operator, you are most likely not  obligated to file this report. In the spirit of "public service", I think it is still warranted.

 

Roger, I hear what you are saying. It is significant that you have never observed this condition given the number of aircraft that you have inspected. Maybe this is not a fleet wide problem that would rise to the level of a Safety Directive. Nonetheless, because of the nature of the system (flight control attachment points without redundant safety features), additional inspection procedures might need to be implemented (SAIB from the FAA). The SLSA difference lies in the fact that these manufacturers control the inspection procedures. Absent a Safety Directive, no one is mandated to do anything (inspection wise), that the manufacturer does not specify.

 

As these aircraft age, there will undoubtedly be situations that arise, that uncover shortfalls in their design. We should all work together to insure that these issues never make the News.

 

Doug Hereford

[Anticept]

Thanks for the note on the MDR. I'm going to let FD get a chance to look into the issue first. I personally think it SHOULD be a safety directive, given the choice of not using a castellated nut. Someone could have been hurt if this was not caught, and it's a pretty simple and minor correction.

 

As for the locktite: that's exactly what I did. Some good old 243.

[procharger]

Good info to have thanks be safe out there. I will check mine Sat.

[Runtoeat]

Can both the front and rear of the cable where these nuts occur be observed easily?  As I understand it, the front one can be checked by removing the tray and looking into the tunnel.  Does one need to remove stabilator to look inside the tail?

[Tom Baker]

I don't think the nut that Jacques pointed out is the one that was loose on Corey's airplane.

[Jacques]

Tom ..you are  right   I was just mentioning the one that came loose on mine

 

Corey is talking about this one  (red Arrow)  revove the tray to inspect

 

blue Arrow is the rear one.   just look Under the stab

 

 

 

.

[Jacques]

and these nuts SHOULD BE castle nuts & cutter pins

 

from the Parts Manual

[Tom Baker]

and these nuts SHOULD BE castle nuts & cutter pins

 

from the Parts Manual

 

At least that is what years of tradition working on airplanes tells us, but Flight Design chose to do it differently. The way they did it should be fine, until the ball end freezes up.

 

Corey, I think I would check the ball end to make sure it is OK.

[FlyingMonkey]

There's nothing really wrong with lock nuts.  The big problem is when they get cycled too many times and lose tension.  If they are in critical areas they need to be replaced when removed.  

[Jacques]

''No self-locking nut shall be used on any bolt subject to rotation in operation unless a non-friction locking device is

used in addition to the self-locking device.''

 

this is a quote from the Design Standards for Advanced Ultralight in Canada,,.. which the CTSW is.

 

but.. are these bolts subject to rotation..since they are in a ''ball' that is..?

[Tom Baker]

The whole point of having the ball is so the bolt can be tightened down so it doesn't rotate. When the ball freezes up then you have an issue. Part of my inspection procedure is to make sure the ball end can rotate.

[Doug G.]

The maintenance manual as well as accepted practices say not to reuse Nylock (self-locking) nuts.

[Doug Hereford]

Tom,

You beat me to it. I agree with your point about the ball inside a rod end. I like to refer to these assemblies as bearings (many IPCs do to). As long as

the bearing performs as designed, the fastener is not subject to rotation. That is why I said that I am very curious as to why Corey's situation happened

(inspect the bearing).

 

The standard airworthiness world obviously does not trust the rod end bearing, as it requires additional safety features.

 

One point on Loctite: In my opinion, Loctite is a very poor choice for use in situations where a fastener may be subject to rotation. It is not designed to work in these cases. Another draw-back to its use in aviation is the fact that it cannot be visually inspected for condition. There is no substitute for

mechanical safety features on critical systems.

 

Doug Hereford

 

PS, I have reused fiber lock nuts, and other types of lock nuts many times. That being said, good judgment must prevail. If the locking

feature is not working, the fastener should not be reused. I have also found (on a number of occasions) where a new, out-of-the-box fiber

lock nut is either missing the fiber ring, or it does not perform correctly..................Moral of the story is to ensure that the

fastener you are installing meets its design requirements whether new or not.

[Tom Baker]

Unless they have replaced the elevator cable on this airplane, which I don't think has happened. The nut likely would not have been removed and reinstalled.

[Doug Hereford]

Which tends to rule out a maintenance induced condition.......This makes the situation even more concerning. Back to Safety Directive?

[Runtoeat]

Jacques, thanks for the pictures.  Regardless whether someone files a form or not, I'll be checking these fasteners on my CT.

[Anticept]

The bearing rotates freely.

 

As for locktite: maybe that's not an ideal function, but it will work until we hear back from flight design. Plus, a little dab of torque seal helps to see if it's rotated.

 

Also, the bellcrank does not have a bushing from what I saw. It can grab the bolt and rotate it. There are washers between the nut and bellcrank to reduce friction, but I still don't like it, and would prefer a castle nut and cotter pin.

[Doug G.]

I seem to recall something negative about using locktight on Nylock nuts, it came from Brian Carpenter. Did anyone else hear that?

[Anticept]

It was probably considered to be a "cheap fix" for worn fiber nuts. If a fiber nut can be moved by hand fully engaged, it's junk and should be thrown away.