shaboogamoo bob Posted February 18, 2003 Report Share Posted February 18, 2003 I am one of the lucky mechs who has one of the lemon B3's that have roll pin failiers in the torque tube. My failiers happen on an average of 66 hours after install of a new or repaired MO1. I know of several other companies that fight this obvious design flaw. Anyone out there with the same frustration? Its too bad they didn't use the same torque indication as in the 1B or 1D1 engine. The French have our last Mo1 and our Freewheel shaft in France(hiccupp) right now giving it a look. There is a new repair scheme that puts a collar over the roll pins and also drills the pin holes a little deeper. Lets hope this works. I need a hug. Shaboo Quote Link to comment Share on other sites More sharing options...
Lu Zuckerman Posted February 18, 2003 Report Share Posted February 18, 2003 How exactly are the roll pins failing? Consider yourself hugged. Quote Link to comment Share on other sites More sharing options...
shaboogamoo bob Posted February 19, 2003 Author Report Share Posted February 19, 2003 Where to begin. Inside the linking tube is the referance shaft which has a castlated assy. and is matched with another castlated assy.on the freewheel shaft (I think). The castilations are facing each other and are "engaged" for the lack of better words.These are picked up by a mag sensor which converts the interuptions of the castlations into a synthetic a/c signal and at zero torque or at rest the referance shaft and forward shaft castilations are at equal distance. My basic caveman understanding is to think of a heavy cable at rest and then twist it with torqe. The cable is attached to one end of the assy and the other side is attached to the Freewheel shaft.As torque increases the distance between castilations changes sending a different signal to the T4 conformation box mounted on the linking tube then on to the DECCU. The roll pins in question hold the aft castilated assy onto the reference shaft. The roll pins have been coming loose, sheering or coming out all together. This is what drives the BFF inspection to check the mo1 and mo5 mag plugs. You are looking for full or parts of roll pins. Most of our failiers have the roll pins working loose but once we found half of a roll pin on the mo1 mag plug. The repair scheme that TEC is talking about places a collar around the outside of the reference shaft on top of the roll pins to give them added support. The roll pins are spring steel and are mounted through an aluminum housing. The CHP in Redding Ca had either 8 or 9 roll pin failiers on one bird alone! OK forgive me on my spelling Quote Link to comment Share on other sites More sharing options...
Large Toole Posted February 19, 2003 Report Share Posted February 19, 2003 Good posting bob, we operate 4 of the AS-350 B-3's for EMS. S/N 's 32xx thru 32x5. The first torque tube roll pin failure was 3 years ago. It was discovered while inspecting MO1 chip plug. The pin was attracted to the chip plug after it dislodged itself from the torque tube. Just as you described in your posting. Sounds like you have been there and done that. The second failure was on another airframe and engine combination 14 months ago. First indication was the repeated failure messages after flight. I'd have to go back to my records for message code numbers. Anyway-borescope inspected torque tube and pins thru the mag pick-up hole revealed one pin dislodged and on its way out from the shaft. We haven't had this problem re-appear for a short time since. Maybe we are due...PBH...PBH...PBH... Quote Link to comment Share on other sites More sharing options...
Lu Zuckerman Posted February 19, 2003 Report Share Posted February 19, 2003 I tried to follow the description of the installation and it appears that like other applications the roll pins secure two elements together and when in operation there is a shear load across the roll pin. The roll pins either break or, they come out. Here is the problem as I see it and, there may be several parts to the problem. 1) The shear loads may be higher than anticipated.2) The roll pins are not made of the correct material for the application3) The roll pins were not properly heat-treated. In this case the roll pin material can end up being too brittle or, it can be too soft. Roll pins are a common piece of aircraft hardware and they are basically a spring and as such have the same failure characteristics as a spring. Because of their commonality the airframe manufacturer will purchase them in high numbers. Also because of their application (non-critical) the airframe manufacturer will not specify batch testing of the roll pins. I work in Reliability, Safety and Maintainability and one of the things I do is prepare Failure Modes Effects Criticality Analyses (FMECA). One of the things that must be considered in that analyses is what is known as “Batch Sensitivity” which means that if one part of a given type can fail then all parts of that same batch can also fail. This could account for all of the failures of the roll pins that are being reported. Placing a cover over the roll pin does not solve the problem. They can still fracture or get loose but they can’t come out. Aerospatial should re-evaluate the design loads and/or check the remaining roll pins for proper material and heat treat and if they find a problem, they should purge the pins from the supply and production systems. I would like to aadd the following: When the roll pins fractured did the fracture occur across the diameter of the roll pin or did it occur across the length of the roll pin. If it occurred across the diameter it could mean that the shear loads are high as well as the possibility of faulty heat treat and if they occurred along the length it is a sure sign that they are too BRITTLE. The brittleness is caused by excessive hydrogen in the metal. The hydrogen is removed using a vacuum process after heat treat. If this is not done you get hydrogen embrittlement. :cool: Quote Link to comment Share on other sites More sharing options...
shaboogamoo bob Posted February 19, 2003 Author Report Share Posted February 19, 2003 Our roll pins usually just back out 1-2 mm. The one that did break off and was found on the mo1 chip plug came off at a 45 degree angle and is at the very end going in about 3 mm. There has been discussion about frequncy causing the damage either from the main gear box or the engine itself in particular the MO4 has been reported to have been at upper limits. Thats very interesting what you have stated here. Great follow up. Shaboo Quote Link to comment Share on other sites More sharing options...
Large Toole Posted February 20, 2003 Report Share Posted February 20, 2003 I went today and looked it up.Here is the Turbomeca Service Bulletin for Arriel 2 engines."No. 292 72 2081 dated original issue 07.11.2002. Incorporation of modification TU 81A. Purpose- To prevent liberation or loosening of the torquemeter phonic wheel securing pins. Description- This modification consists in adding a retaining ring around the securing pins of the torquemeter phonic wheel on the power shaft assembly."Its goes on for 7 more pages with the usual Turbomeca verbige. I can e-mail a copy to any one that is curious.Hope your next engine has TU 81A complied with. The Large One... Quote Link to comment Share on other sites More sharing options...
Bell214B Posted February 20, 2003 Report Share Posted February 20, 2003 You can also find Turbomeca SB's etc. since 2001 on www.turbomeca-support.comYou have to ask for a log-in and it may take a couple of days. Quote Link to comment Share on other sites More sharing options...
Large Toole Posted March 16, 2003 Report Share Posted March 16, 2003 The Turbomeca North American Customer 4th. annual symposium slide show(powerpoint)that was held on December 18, 2002 in Las Vegas, Nevada has a good picture and illustration on slide #110 of the Arriel 2B torque tube pin failure and repair scheme. Regards...the large one... Quote Link to comment Share on other sites More sharing options...
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