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Door latch mechanism failure and repair


FredG

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While flying today, I noticed it was unusually windy inside the plane and then observed that the passenger door was not fully closed(!).  

 

I landed and found that one of the three tapered "tips" of the door latch mechanism (I would call them tapered or beveled latch pins, myself, but FD calls this part a "tip") was no longer protruding from its forward position on the door when the latch handle was in the locked position.  

 

I removed the door and opened the inspection panel and found that the small cross-drilled pin ("SBB04x11" according to the parts manual) holding the "tip" to the "forward rod" had come loose.  Ordinarily this pin is kept in place with a cotter pin.  I could not get the forward rod out through the inspection port (too long), so after fishing the pin out of the bottom of the door, I installed the tip on the rod and inserted the cross pin and a new cotter.  

 

Getting the "tip" through its hole in the forward part of the door required some dental floss and a bit of tape, not to mention a borescope.  About an hour of cursing and a small amount of blood later, the door latch mechanism was as good as new (or better, I hope).

 

I guess I should inspect the left door for a similar impending failure.  Note that if the tip were to separate from the rod while in the locked position, it might be possible for the door to be stuck shut regardless of the position of the latch handle. I would not be happy with such a problem.

 

For your information, only!

 

Fred

2006 CTsw

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Hi Fred,

 

I agree. PITA fix.

 

I have done 2 of these. One bottom pin and one front pin. The front pin was a major PITA and it was done at a Page, AZ Fly-In a few years back.

I haven't looked, but wouldn't a borescope and mechanical fingers through the inspection panel be easier?
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Dick,

 

Once the door is off the plane, getting the loose parts isn't especially difficult (tilt and shake).  One problem for me is that I was unable to get the forward rod out of the opening in the door (after removing the inspection cover).  I did not remove the bolt holding the door closing lever bell crank, so I can't comment on whether that would have helped.  In my case, all the work was done inside the door through the inspection hole (the work was simple stuff, but tedious because of the limited work space).

 

The part requiring some creativity was getting the tip back through the forward guide hole in the door.  Holding the rear end of the rod doesn't help because there is a pivot between the rod and the tip.  Note, there is only a millimeter or two of clearance between the diameter of the tip and the size of the hole in the door which serves as its guide.  So, for that I used a small pice of masking tape (not even full wrapped around the tip) to hold a strand of dental floss so I could gently guide the tip through the hole.  Anything larger than floss or another slender thread will block easy passage of the tip through the hole.  

 

In all, the repair is more tedious than technically difficult, if that makes sense.  

 

Fred

2006 CTsw

E-LSA

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I agree with Fred.

It isn't worth removing any parts for an inspection. You will regret it.

getting a bad part out is fairly easy. Putting parts back in is the PITA. There is no room to work and the parts and holes through the door don't line up straight so trying to fish everything through will challenge you temper. I always lube at every inspection door pins and holes to reduce any binding and stress on parts.  

 

An ounce of prevention here is worth 50 lbs. of fix.

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An ounce of prevention here is worth 50 lbs. of fix.

I always lube at every inspection door pins and holes to reduce any binding and stress on parts.  

 

Again . . . food grade lithium?

Oops . . . please pardon me, I meant silicone.

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Ha, the food grade lithium might help some of us with our mood!

 

I put some quality moly-based grease on the pivot points and a very light coat on the "tips".  Any lube that will stay put and not harden should work, I think.  

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The reason for food grade silicone is most of them don't have harsh solvents, distillates or other harsh chemicals that may damage plastics. I use either 3m silicone food grade paste and the majority of the time I use INOX (form Ace Aviation or online) food grade silicone spray for all our moving parts.

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The reason for food grade silicone is most of them don't have harsh solvents, distillates or other harsh chemicals that may damage plastics. I use either 3m silicone food grade paste and the majority of the time I use INOX (form Ace Aviation or online) food grade silicone spray for all our moving parts.

 

Thanks Roger.

My door latch seems a bit stiff, that lube should make a big difference.

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Roger, the INOX I'm familiar with is lanolin based and is food grade. It comes in sprayable liquid and believe also a paste?  I think you turned me on to INOX.  It isn't sold here in Michigan and I have to buy it in Ohio.  It says good down to -20F (or maybe -40F?) and is the only lubricant that completely quiets my screw drive garage door opener by preventing chattering during the winter months.  Even low temp Lubri-plate doesn't do this.  I use INOX on all my CTSW moving parts.

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Roger, the INOX I'm familiar with is lanolin based and is food grade. It comes in sprayable liquid and believe also a paste?  I think you turned me on to INOX.  It isn't sold here in Michigan and I have to buy it in Ohio.  It says good down to -20F (or maybe -40F?) and is the only lubricant that completely quiets my screw drive garage door opener by preventing chattering during the winter months.  Even low temp Lubri-plate doesn't do this.  I use INOX on all my CTSW moving parts.

 

Are you sure that's not hand lotion? . . . :)

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