VG-21 Squadron


Varga News:

September 2010

As I assume many of you know, several people worked on the resolution of a vertical stabilizer spar crack issue that resulted in the latest Service Bulletin and Airworthiness directive.


This episode of the news will discuss the process that got us from discovery of a serious problem to fixing it but first, we appreciate that Brian Tetrault would like to acknowledge and thank those responsible for the effort that it took to get his airplane back into the air again and to get yours repaired and flying safely again...


Vertical stabilizer spar reinforcement

As the owner of the Varga with the first vertical stabilizer spar crack, I wanted the Varga Community to know how much effort and tireless volunteer work went into finding a fix for our birds.  I have asked Max Bishop to publish this in the next newsletter unedited as I believe he would tend to minimize his part in achieving the end results.


The driving forces were Lee and Pat Beery and Max Bishop.  It started on July 6th, 2009 and finished up administratively at least on the 23rd of February, 2010.  There were one hundred and seventy pages of correspondence, twenty eight photographs, thirty four diagrams, an FAA Airworthiness Concern Sheet, an FAA Service Bulletin and an FAA Airworthiness Directive. The effective date of the AD is March 24th, 2010.


Lee and Max drew from their many years of experience in the industry.  They tackled the problem and were steadfast in pursuit of an equitable solution.  Their emails showed up on federal doorsteps practically each day.


Tom and Tina Wasson of Tom’s Aircraft Enterprises and Steve Colvertson of Steve’s Aircraft Repair both at Lampson Field in Lakeport, CA. gave much with their insight and innovative thinking.  Loren Perry, the current Type Certificate Holder, published the service bulletin that Lee and Max wrote.


On the Federal side were Brook Stewart of the Sacramento FSDO, Hal Horsburgh and Cindy Lorenzen of the Aircraft Certification Office in Atlanta .  For the FAA to approve of this fix, this quickly, all the key players had to keep the lines of communication open and the exchange of information flowing.  We thank them.


For a certain few, this was a labor of love and to them we owe a great deal.


Brian Tetreault N1901A

In addition to the thanks from Brian, Maintenance Item #25 has been added in which Lee Beery has written a short synopsis of the events and his own thank you for help along the way to the eventual creation of the Airworthiness Directive.



  (by Lee Beery)


This Maintenance Item is to give the VG 21 members some insight into the new AD 1020-04-14.  As you recall in the last NL, Max reported the problems found on the vertical stabilizer on several planes.  I will tell you briefly what transpired.


Being a licensed mechanic, I must report such findings to the FAA, which I did, and they promptly grounded the two planes [Brian Tetrault and Lee Beery's] .  The FAA Designated Airworthiness Representative for our area said the repair was beyond his authority and directed us to the FAA Designated Engineering Representative [DER].  The DER wanted $1600.00 for the fix on the primary aircraft and then $800 each for every aircraft that was repaired after that.  This left us with paying a huge price for his service or doing our own design work and getting FAA approval by using a “one time” field approval, a form 337.  It took four submissions of a 337 and 60 days. The actual time to disassemble the tail, fabricate, and install the doubler, reassemble the tail and check everything out was only about 14 hours.  There has never been so much activity at the Varga Service Center – ever!  Tom, of Tom’s Aircraft, spent many long hours working on this project.  Steve of Steve’s Aircraft Service provided a lot of insight as to how to work with the FAA.  Approval for the second Varga came within another twenty days.


I was told by more than one rep from the FAA that what we achieved was rare and could never be done in less than a year.  I’m sure this would have been true had it not been for Max Bishop who was called upon many times for information and we even called up retired aircraft engineers who I worked with before I retired.  The biggest thanks goes to FAA Engineer Horsburgh as he provided guidance the entire time.  There was a great deal of technical data going back and forth between mechanic ranks and engineering gurus.  Pat, of course, was doing all of the correspondence for me so many thanks to her. 


Max and I collaborated on producing a Service Bulletin for Augustair and I want you to know it was 3 pages long, not the 22 pages that were published.  On the negative side of all this, some individuals feel we created all this just to make this miserable and to spend their hard-earned dollars.  Guess you can’t make everyone happy! 


The following is Max Bishop's version of the Vertical Stabilizer issue: 


Where it all started and how and more than you ever wanted or needed to know…

I first learned about this problem years ago while I was Varga Aircraft's Engineering Manager just before Varga closed it's doors in June of 1982…

When someone notified Varga of cracks in a vertical stabilizer forward spar, on what I think may have been a Shinn, I investigated the problem and submitted a report to the FAA describing what I had learned and providing a potential solution, very similar I think, to what the current Service Bulletin provides… 

After the factory shut down, shop foreman Al Wilson and I were running a sheet metal business out of Varga Aircraft's hangar and I was still there when the report was returned to Varga with a reply from the FAA stating that, since this was the only instance of cracks like these that they knew of and that it should be detectable in a normal annual inspection, no further FAA action would be taken unless and until there were more reports of similar instances.

My report and the FAA letter may still exist somewhere in Varga's archives but, at this point, it's existence is irrelevant...

At the time, I was a bit worried that the problem might resurface again some day but, since it was out of my hands, I had no choice but to let it go...

In any event, I was not surprised to hear about a crack when I got an email from Lee Beery but I was surprised to learn that cracks had traveled across the spar web without being detected sooner. It was fortunate that there was no catastrophic failure in flight.  Fortunately, this was discovered in time there was ample opportunity to warn Varga, Shinn and Morrisey owners of the problem. That being the case, I think that I was not as alarmed as those who discovered it or as was the FAA when they were first told.  I will tell you why and continue a discussion about the cause but first I will digress a bit to give you a little perspective (both personal and historical) about cracks... Much of this may seem unrelated to the current issue... but I'll get there...  ;-)

In about 1978, I think, we began to get reports of cracks in elevator control horn flanges on airplanes. After some review of he reports it began to appear that most, if not all, of the airplanes with cracks were being used in flight schools or for rent by FBOs.

A service bulletin was issued requiring 25 hour mandatory inspections and an Airworthiness Directive soon followed.

One airplane owner was so concerned that he brought his airplane to the factory for us to test. One of the first things that we notices was that the aft fuselage was dented on each side. This appeared to mean that the elevator horn balance arms were vibrating very severely from side to side. But when we did a vibration survey, flight tests and load tests on the part, we couldn't find anything that showed the airplane or parts were loaded or operating outside of the what original design data said it should be and we could not repeat a vibration a severe as the ones causing the aft fuselage dents...

Even though we couldn't duplicate the problem at the time, we knew it was a serious issue so, on advice from n engineer whose opinion was respected by the FAA we changed the elevator horn from aluminum to steel to improve stiffness and strength. Vibration, flight and load test data was about the same as with the aluminum part and after the design change was accepted by the FAA, we started shipping replacement parts to owners who found cracks.

Unfortunately, after we began to ship the steel parts, even with the Service Bulletin and the AD in effect, there was a fatal accident caused by the failure of an elevator horn...

The airplane that crashed was one of five being used by a company with a Navy contract to test Cadets for suitability as pilots. My understanding was that each student got 15 hours of instructed flight and if good enough, the Cadet was qualified to go on to Navy flight school...

After we shipped new elevator horns to the flight school so that they could continue their program, I got a call from an FAA manufacturing inspector asking if I wanted to go to visit the flight school to help him investigate the problem... I accepted and when we got there, the first thing we did was review the aircraft logs and the four elevator horns that were removed from the airplanes that had had them replaced and were still in use. While the FAA guy examined the logbooks, I looked at the elevator horns we had been given. The logbooks did have all had the correct signoffs at the required 25 hour intervals. Unfortunately, though one of the service bulletin requirements was to remove the paint in the flange area in order to accomplish an inspection, first thing I noticed was that, on none of the four remaining elevator horns, had the paint been removed. 

After the FAA pointed this out to the manager of the company, I was called into his office for a private discussion... Apparently, he had called his lawyer to discuss the apparent discrepancy between the logbooks and the parts and, upon legal advice, I was told that, though I was allowed to stay on the premises, I would no longer be allowed to examine the planes or parts while the FAA representative finished his review so I wandered around in the fog on the ramp until it was time to go home...  ;-)

In the process of our search for a solution, we hired a vibration specialist (a guy named Sandy) to analyze the problem for us. Within a few days of our call to him, he came by with his test equipment, instrumented the back end of an airplane with accelerometers and strain gauges and climbed in the back seat with his recorder to do a flight test. When he reviewed the flight test data on his analyzer he quickly determined that the problem was a resonant frequency that was at about twice the elevator's natural frequency of about 1200 cpm that was so strong during an accelerated stall that the loads at the elevator horn flange, where the cracks were occurring, were greater than either the aluminum or steel material could handle over time. It turned out that the elevator horn/balance weight assembly was a near perfect tuning fork when excited by an accelerated stall when the engine speed was about 2400 rpm.

With this information in hand, Sandy suggested a company that could do redesign of the part for us so we contracted with them to do the job. 

Sometime later, along with a bill for $7,000, we were sent a drawing of a proposed elevator horn and balance arm assembly that was made from solid 4130 steel that weighed twice as much as the whole elevator.

Dismayed by the design I had in hand, I called Sandy to tell him that this was unacceptable and ask him what I should do... He told me that he had an out of state job to do in a couple of weeks and, on his way back in his Twin Beech, if I would come up with a few elevators designs that I thought might work, he would stop by and test them to see which was the best...

By the time he got there, I had 5 different elevator horn designs for him to test. The simplest (cheapest) was just an existing steel horn with gussets welded at each flange and the most complicated (expensive) was the elevator horn design that you now have on your airplanes. I don't remember what the 3 other variations were but I do remember that the test Sandy did was simple, fun and interesting...

Once he had his analyzer set up on a table in my office area, he had me attach each horn, in turn, to the table with C-clamps and after he attached a couple of accelerometers to the horn, he just whacked it with a hammer to see what it's natural frequency was... 

After the whacking... errr... testing was done, it was obvious to Sandy that any of the horns would work but, for political reasons (both FAA and customer), it was decided to go with the stiffest (and most expensive) design. 

From there we proceeded in the next couple of weeks to install a new horn on an airplane and have Sandy come back, instrument the new horn and do a flight test... The result was that the stress on the part went from over 90,000 psi in the old part to less than 10,000 psi in the new...

With that data in hand, we got FAA approval fairly quickly and began manufacturing and shipping the new parts as fast as we could.

OK... what was the point of this long preamble that apparently has nothing to do with the vertical stablizer? Well... mostly it's about lessons learned about vibration, fatigue and stress but it's a journey and I'll get there...

Here's another part of the journey.  

The Varga Taildragger was originally designed and built by one of our dealers named Hibbard Aviation. In trying to sell airplanes, Hibbard had gotten lots of  inquiries about a tailwheel Varga but, heavily into the certification process of the Model 2180 Varga couldn't afford the time an energy required to build and certify a taildragger as well so Hibbard chose to go the STC route and design and build their own.  It took many months but they were eventually able to convert a Model 2150A tricycle gear plane to a taildragger and get it certified. 

Interestingly, about the time that Hibbard finished there certification, a new partner in Varga brought an infusion in cash that allowed us to buy the tailwheel STC from Hibbard and add the 2150ATG to the 2150A and the 2180 model that had been recently certified.

Unfortunately, as it happened, the STC was for a 2150 and now, with the availability of the model 2180, all of our customers with deposit money in hand, wanted a 180HP taildragger instead of a 150HP one...

This meant that incorporating the taildragger into the production line required the addition of the Model 2180 to the STC and lots of extra work for Max and others.




From: Joseph M. Atkinson 
Sent: Thursday, April 01, 2010 1:05 PM
Subject: Completed Varga Stabilizer AD


Hi Max – in case you are keeping track, I just wanted to let you know what we found on my Varga 8417J, a 1980 model 2150A.  There were a total of 3 small cracks.  2 were in the left side bend radius, each about ½ inch in length, of negligible width and easily visible.  The 3rd crack was in the right side bend radius, about 3/16 in length, and was so slight in width so as not to be visible until exposed by the dye-penetrant.


Oddly, one of the left side cracks that was too low on the bend radius to be visible in the initial visual pre-removal inspection had previously been stop drilled.  There was only a short, cryptic reference in the aircraft log, from the 2002 annual inspection (I purchased the airplane in 2005), that stated “Stop drilled crack in stabilizer”.  My A&P said that due to its location, the prior stop drill could not have been performed without removing the vertical stabilizer.  There was no obvious evidence, either on the aircraft on in the logbook, that the tail had ever been removed prior to this week.  Moreover, that stop drill didn’t seem to touch the metal splice plate in even the slightest  way, despite the fact that the splice plate lies flush against the spar in that location, so the origin of that prior stop drill remains a mystery.


My A&P complied with the damage remediation requirements in the service bulletin, and the aircraft is now ready to fly again, which I hope to do this weekend.  Thanks again for all of your work in getting the word out.  


Joe Atkinson  







Max Bishop


I will continue provide the VG21 Newsletter on the web site and will expand and improve it as time and circumstances permit. Those members who request it will receive a hard copy.


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