A WEAK LINK?

February 2000

With a 1000 hour gear check done on my 1959 PA-24 only a year ago, I thought this years annual inspection would be a snap. Everything went well; the engine and airframe were all o.k., and it was time for the gear check. The plane was on jacks for the IA to have a look.

So, into the cockpit I went. Master "on", and up went the gear, with the IA under the plane watching how everything worked. Then, he asked for gear down. Then up. Then down... and said there was something unusual he wanted me to see. With the gear half down, I got under the nose so he could show me. He pointed to the clevis at the end of the left drag link on the nose gear and showed how it would move if pressure was put on the nose wheel. He wanted me to see what he had observed with the gear in motion so we traded places; him in the cockpit and me under the plane. Sure enough, as the gear retracted, there was movement on the end of the drag link as the gear neared the up position and stopped. I could actually see a slight movement in the clevis.

This is the drag link clevis we were looking at

We discovered the drag link clevis had no torque. It was loose, in spite of being held in place by an "updated" reinforcement bracket that had been installed 34 years ago in compliance with AD 65-25-03, and Piper Service Letter No. 445, dated April 21, 1965. An earlier Service Letter No. 336, also done, called for a heat treated clevis marked "HT".

Updated reinforcement bracket per Piper SL 445 (above)

Heat treated clevis marked "HT" per SL 336 (below)

The 1000 hour gear inspection, only recently done, does not call for the clevis torque to be checked. It "looked" okay at that time, and the AD for the clevis had been complied with and was not recurring. Everything was legal. But, the drag ling clevis was loose, and it was difficult to detect. It was an unsafe condition. How long had it been loose? I don't have a clue; I've had the airplane for 21 years and as far as I know the clevis torque had never been checked. A more important question is; how long would it have gone before breaking? Thoughts raced through my mind about what could happen to my brand new prop and having to tear into my freshly rebuilt O-540 if the clevis broke... not to mention the sheet metal repairs.

But, perish the thoughts; we had to get on with fixing that loose clevis.

The clevis is shimmed with one or more shims between the clevis and drag link to give it the proper spacing for connection with the push-pull rod. On the early PA-24s, the clevis is threaded into the drag link and must have a torque of 13 to 40 foot pounds when it is aligned with the drag link. It is then held in place by a "drag link clevis reinforcement bracket" as shown in SL 445. Apparently, over the past 34 years, the shims have worn enough to relax the torque and cause looseness in this connection. Another thin shim was fabricated and added to make the connection tight and restore the nose gear to a relatively safe condition.

From now on, checking for looseness in the drag link clevis will be a standard part of my annual inspection by watching for it as the gear retracts. Since finding my loose clevis, I've heard of others. One shop that regularly sees Comanche gear estimates up to 80 percent are bad.

Mine was. How is yours?

 Glenn Plymate ex-ICS 2658