My trim system failed yesterday!
 

As I levelled off at 2500' yesterday, I needed some down trim so I pushed the button...WHOA!!...it pitched UP!

The trim indicator bars worked but not the real trim, so I immediately landed. On the ground, I looked over my shoulder at the trim tabs and heard the trim motor running, both up and down, but no motion of the two tabs, so I got out and walked back there.

Grabbing a trim tab, I moved it up and down, the other one accompanying it!

After I removed the tail fairing, the two cables were still attached to the bellcrank but when I reached in there, it moved up and down, when it shouldn't, since it's a pivot point for the trim servo.

Crawling in the tailcone, we saw the AN-4 bolt, castellated nut and a couple of washers lying close to each other! We searched and searched for a cotter key back there but never found one! We put the bellcrank (F-1095B, page 11-9) back in place and this time, cotter-keyed the bolt, since it's a pivot point, and tried the trim and it worked normally.

My gut instinct tells me that there never was a cotter key installed and this airplane has 5+ years and over 500 hours on it and that the nut, then a washer, then the bolt, all progressively fell out over the years and had never been checked during condition inspections!

For all of you -10 guys, remember, it's a rather difficult area to inspect because it's underneath the supporting structure and you probably have to crawl back there to really check it over well.

The airplane, nevertheless, stayed quite controllable, although with considerable forward pressure to hold the nose down, since the tabs had moved downward when I first pushed the "down" button, instead of up, because the whole assembly moved toward the front of the airplane, pulling the tabs down, and the pitch up.

Whew! Yes, I did say a "Thank You" prayer:)

Best,

Wow
 

Glad you're safe! Sobering lesson, thanks for sharing.

My Goodness Pierre!! NOT FUN!! Glad you are OK and thanks for reporting this. I'm going to check my -4 for all attachments. I'm in middle of inspection time. This gives me added incentive to be cautious & focus on what I'm looking at. You've done us all a great service.

Thank you & happy flying,

The Waddington Effect
 

Be very careful flying your airplane after an annual/condition inspection. NO passengers on the "acceptance" flight.

Here's why:

http://livingstingy.blogspot.com/201...on-effect.html

Best,

Whew!
 

+1

Congrats Pierre! You dodged a large caliber OOPS. Much easier hearing from you how it happened than reconstructing the pile of aluminum without your help! At least, the fellas at the NTSB use that phrase...

Carry on!
Mark

:eek:


Annual coming up....extra attention will be paid there.

Thanks for the lesson Pierre!

I've added this particular item to my "checklist" just to be sure its not missed during an annual. I think if I were you, I'd probably be looking at the rest of the control attachements just to be sure there wasn't a similar condition somewhere else.

As for the "Waddington Effect", I agree a post maintenance flight test is never a bad idea. It was required in my old job when any task was performed that could effect flight characteristics where ground testing could not ensure proper operation (flight control rigging for example).

However, some folks may interpret this to mean (and take literally), "if it ain't broke don't fix it". The whole premise of aircraft maintenance and inspections is not to wait till something breaks to fix it. Things wear out over time and most failures show evidence of pending failure, preventave maintenance is a critical part of aircraft safety and reliability!

I just did my annual. In that area I use a mirror and a flashlight. I then take pictures with my iPhone at all the angles needed to see everything by just reaching in from the back. I can then review on the spot or at home for confirmation that all is well. Pictures work great in many areas. Reaching in to confirm jamb nuts are tight is a must to.

It is nice to know that the tabs did not flutter. :eek: thanks for testing:D

Glad it worked out well, bet the heart was sure racing.

I agree, cell phone camera's are great for inspecting hard to see area's!