Saga of the 337 Annual

Normally an Annual is not a very involved process.  You run the engine(s), check the airplane systems, pull lots of panels and then inspect, inspect, inspect.  An IA will always find something, even if the plane has not flown since its last annual - there is always something to correct.  This is an annual which neither the owner or myself thought would be too far out of the ordinary.  The owner purchased the airplane a year ago and it had a fresh annual then.  He flew it for a year and brought it to me when its annual came due.  Now I have included a lot of pictures below because as the annual progressed, so did the "problems" encountered.  Clicking on any picture will "full size" the picture - then use your "back" button to resume the "saga".

Front Engine    This is a Mattituck remanufactured engine with only 400 hours on it.  Cylinders two and four have low compression and are leaking past the exhaust.  Staking the exhaust port does not correct the issue and a borescope confirms the exhaust valves have burn marks.  Off come the cylinders and out to Gibson they go.  Note, the exhaust ports were starting to erode; more on this below.

Rear Engine    This is also a Mattituck remanufactured engine with only 400 hours on it.  Cylinder four is leaking past the exhaust.  Staking corrects the issue; we re-run the engine and the compression again; all is good.  Borescope is clean.

While checking the rear engine it is discovered the cowl flaps don't work.  Seems the feedback cable (which was just replaced seven months ago) is bad; the end unraveled [part number S1244-17].  Figures, the warranty is six months from Cessna.  Need a new cable - and when the cable failed the motor sheared its pin.  Thank goodness the pin sheared as the motors are a cool $1,500 to replace.

Rear Exhaust    What is that ? Other than de-paneling the rear engine and doing the compression check I really haven't started the inspection of the engine area.  But looking down at the rear exhaust there is a crack in the mounting flange.  Further investigation the muffler is cracked along the mounting flange - this is a new muffler that was installed with the new engine.  Seems during the last annual the muffler had been pulled and re-installed - the problem is the mechanic "torqued" the rear mount bushing preventing the muffler from swinging.  Not only did the muffler crack along the flanges but the left exhaust stack flange was cracking. 

Well, seeing this one has to wonder about the rest of the exhaust.  Hmm, checking the torque on the exhaust stacks revealed most were not proper and several of the stacks had blown gaskets.  Fortunately, cylinder exhaust faces were not eroded.  Before sending the rear muffler and flange off to Dawley for repair I decided to go do the inspection of the front exhaust system.

Geeze, guess what ?  Same mechanic.  Both the left and right firewall mount bushings were over torqued which cracked the lower mounting clamps ($30 each) and caused the exhaust stacks to pull three exhaust studs and blow five of the six exhaust gaskets.  Here you can see the broken left and right clamps next to a new clamp.

With these broken clamps the mufflers were now hanging down and resting on the cowl flaps.  Not good for the cowl flaps.  You can see where the mufflers wore into the cowl flaps.  Good news is the mufflers were not damaged and the rest of the front exhaust was in good shape.  As this annual proceeds you'll understand why any good news is important.

So the compression checks are done, oil is drained, plugs have been removed for cleaning, two cylinders on the front engine have been pulled and sent off, the front and rear exhaust systems have been completely removed as there are two studs which need to be fixed and all the gaskets need to be replaced.  The rear muffler has been sent out for repairs. 

When I pulled the number 4 and number 6 cylinders I got a small surprise on the baffling.  Whomever installed the engine didn't pay close attention to how the baffling should be installed.  While I don't have pictures of this the cylinder base baffles for 2 and 6 were reversed.  While it may not seem like much it will explain the hot running cylinders.

As I was pulling the number 4 and number 6 front cylinders it became extremely clear why the front engine prop didn't cycle the way I felt it should during the engine checks; it was slow and sluggish.  I had it on my list of things to look at and while pulling the cylinders it became very apparent why the front prop did not cycle as it should.  Not the best looking prop control cable around.  A quick check of the throttle and mixture cables revealed that if I'm gonna change one I might as well change all three.  A call to Don at Commodore and I've got three cables on the way for the plane.

Now the owner of the plane has had a few calls from me on the plane so far.  Again, I'm doing the annual inspection - in my book that means I inspect and when I find things wrong I inform the owner and it is their call if it gets fixed or not; of course, I let them know what is required for me to sign the plane off as "airworthy".  If they don't want something fixed, that is on them as I can always sign it off as un-airworthy and then provide them with the list of items making the plane un-airworthy.  So I have called the owner several times now; he is not happy with the exhaust (fix it); not happy with the cylinders (fix 'em); not happy with the cables.  While I explained the throttle and mixture cables could still be considered "airworthy" my recommendation was to change them.  Fix it.

Above the left main gear there is a slight ripple.  The owner and I have seen this before and it appears to be from a bounce where the gear came up and touched the sheet aluminum above it.  Rivets all look good and a respected shop up north had recently replaced the brake line which runs right along the gear leg.  They didn't think much of it so no one else did.  The area still looked as it had the last time I saw it, slight wrinkle, no popped rivets, etc.  I stuck a borescope up the gear leg and found an angle bracket inside cracked all the way through.  Huh, this isn't good.  The interior was de-paneled and you can't get to the bracket from inside - the ONLY way to get to the bracket is to remove the skin.  Called the owner and explained the issue - fix it.

The first picture shows where the crease is and circled at the bottom is the location of where the L bracket was cracked behind the skin.  The skin was drilled off as were all the internal stiffeners; everything had to be cleaned, inspected and painted - there was a fair amount of corrosion.  You'll also see a lot of red around the gear - everything got ZyGlo'd.  In the last picture you'll see a good amount of corrosion.  When the interior was removed the carpet (relatively new) was deteriorating - the owner does a fair bit of volunteer work for the various animal rescue organizations.  Urine is extremely corrosive and in a short amount of time a few accidents have caused a good amount of corrosion.  Yes, the bill is getting very large now.  337s will normally have a black sound deadening material glued to the floor.  This is from the factory and while it may help deaden sound as the plane ages and the glue holding it down fails it actually becomes a catalyst for corrosion as now moisture (urine is moist) can get trapped under the material and attack the flooring.  If you look closely at the last picture above you'll see the corrosion going under the seat rail - the seat rail was removed and  the floor underneath was not pretty.

Another issue was the pilot emergency window needed to be removed so I could get a clean shot at several of the rivets holding the skin.  One would think that a quick tug on the emergency release handle would be all it takes.  Wrong in so many ways.  There are three pins which hold the window in - pulling the emergency release handle pulls the three pins and the window should fall out.  All three pins were corroded - two were finally removed after soaking for two days in Mouse Milk; the third was not coming out, I ended up cutting it out.  Ok, now the window should just fall out - it didn't.  I couldn't even budge it.  There are tangs which the window rests on which are supposed to hold the window in place - the operative word here is "rest on".  Someone had actually bent the tangs around the frame thinking these are there to "lock" the window in place - there was no way this window was coming out; how they even managed to get it in is beyond me.  After several hours of choice words and careful bending and prying the window was out.  Geeze.

To skin the side of the plane the left lift strut has to be removed.  The control cables run up the lift strut so it was not a surprise that one of the cable guides was chewed up.  Heck, surprises are becoming common place with this annual.

 Right about now I am starting to keep the camera handy.  Seems everything looked at has a problem which needs to be fixed.  Ok, the interior is out the side skinning of the plane is moving along - I need to open the gear doors and finish de-paneling the plane.  The gear doors are opened, lets inspect the wheel wells and get them closed back up; maybe we can at least get one area of the inspection checklist done. 

I started the wheel well inspection at the, well, the nose.  Makes sense.  Ohh, you gotta be kidding me !!!  This is not good.

Looking closely at the above pictures you will see how the right rear engine mount tower and the inner right skin of the nose gear tunnel are buckled.  The Nose landing gear down lock casting is actually pulled down 3/8 of an inch.  On top you can see where the tunnel side wall is buckled behind the engine mount tower also and in the last picture you can see where the doubler has pulled rivets.

This isn't a phone call - I asked the owner to stop by so we could talk.  I showed him the damage and let him have a seat.  How was a really great question he had.  Most people would think this was from a bad landing - heck, I thought so at first also.  But looking at the damage there is no way this was from a hard landing - the damage is all wrong for it to be a landing issue.  The force to do this damage could only come from towing the plane.

Then things started to make sense.  Not long after the owner purchased the plane the right brake assembly jammed itself inside the right wheel destroying the brake, the wheel and the axle.  When the axle was removed the plate which supports the brake assembly was cracked and had failed.  Investigating the "crack" the inspection showed that the plate had been cracked for a reasonable amount of time - possibly before the owner purchased the airplane.  I have had a few 337s and have watched folks tow and ground handle them - to the point of watching people "push" the plane back and have it sit on its tail.  What happened to this 337 - most likely someone towed the plane with the brakes locked - and they towed it for a really good distance.  Far enough to heat and crack the brake and far enough to keep continued force on the nose gear and actually "pull" the downlock casting down.

Ironically, I had to fly to California with a friend to bring a 337 back to Delaware.  Guess what, we found the right rear tower had a slight buckle - nothing as severe as what this plane had, but a buckle never the less.  Not too long after that I went to Florida and picked another 337 up there - no problems with that one.  If you own a 337, don't let anyone tow it and when you tow it be really careful.

I gave the owner two choices at this part.  If he turned this into the insurance company there was a really good chance they would just total the airplane.  To fix this problem you have to literally take the complete front end off the airplane and remove a good portion of the nose gear tunnel.  Parts would be hard to get and time consuming to fabricate.  I'm a one hanger operation and while I have lots of time on my hands this is not my full time job.  While I can fix the plan it would be done on my schedule (parts permitting) or we could button the plane up and ferry it to one of the big shops.  While the big shops would not be cheap they could probably fix this in four to six months.  The owner didn't hesitate knowing that bringing it to a big shop would run the bill up to the point where he would just total the plane. 

So begins the new chapter of this annual.  First, remove the front engine and start drilling the front end off.  We need to get into the damage and see how far it goes.  If you look very closely at the downlock casting in the pictures below you can see how it is lower on the co-pilot side than on the pilot side.

As the disassembly progresses you can see how the damage begins to become more pronounced.  With the above we already have a bad downlock casting, the front and rear pieces of the right rear engine mount tower are bad, the engine pan [SHEET 1551010-7] is bad (pulled rivets) and the top doubler [DOUBLER-RH 1552003-4] is bad.  Oh, and the right skin of the tunnel is bad.

Boy, simply amazing how cleaning something up will really show the amount of damage.  The side skin for the tunnel is really in sad shape.  Looking at the third picture you can also see that the interior doubler is also bent in the worst possible place.  Both the side skin and the interior doubler run into the cabin and actually form the tunnel in the cabin next to the pilots right leg and the co-pilots left leg.  Yes, to get to those rivets you have to also take up the flooring on the co-pilot side.  Oh, this just keeps getting better. 

Now to go find the parts. 

Here are the parts needed to fix this:

As one might imagine it was going to be a long hard road to find all the parts.  The support and channels were the easiest to find.  The tunnel skin was turning out to be a major problem.  While I couldn't locate the engine floor pan skin I wasn't overly worried about it; the hardest part would be making the flange for the oil pan.  The tunnel skin though was not going to be a fun fabrication.  I called out to several places and while some had them used they would need to be drilled off.  When you look closely at this piece drilling it off is no easy task - you must remove a whole lot of stuff both inside and outside the airplane including the co-pilot flooring, rudder pedals, heater ducts, nose gear, etc, etc, etc.  Not fun or cost effective just to get the piece.  So I did some computations and put a package together and called Cessna.  The plan was to fabricate the front part of the skin and then splice it.

The Cessna engineering team had this for a week (not bad at all) and then called me back.  They approved plan - no further modifications required; go ahead - fabricate and splice.  Wow.  As I started to get all the ducks in line to make this piece I tried one more source that I had heard about (I'll keep this secret for now.)  Sure enough after three days of searching they found a new surplus skin.  Never fails, does it.  They shipped it up to me and all the fun stuff I mentioned above began (remove the nose gear, rudder pedals, etc.) 

Now, why even bother if Cessna had approved the splice plan?  Simple, I would much rather put the plane back the way it should be than using some alternate means.  Splicing would be a whole lot easier but that isn't how the plane came from the factory.  Since I got my hands on the skin I would install it.

We're going to detour here for a moment.  The nose tire has a slight gash in it warranting its change.  Gotta pull the wheel to work the nose issue and to inspect the bearings.  Off comes the tire and, hmm, sounds like sloshing.  The rims are split and the inside of the wheel has a fair amount of water in it.  The only way to get this much water is to power wash the plane I can can assure you the current owner did not power wash the plane.  As you might expect the inside of the wheels have corrosion and the bearings are shot. 

Stay tuned - more to come ...