Wednesday, April 17, 2013

Two Heads Are Not Always Better Than One

Date Aircraft Route of Flight Time (hrs) Total (hrs)
17 Apr 2013 N21481 5G0 (LeRoy, NY) - GVQ (Batavia, NY) - DSV (Dansville, NY) - 5G0 1.3 1136.2

Smooth was the operative word for the day as Warrior 481 conveyed me home from dinner, illuminated obliquely by an evening sun.

A week earlier, the Warrior was down for annual inspection, a critical time of examination and renewal of that which is worn.  After all, she's 34 years old.

I spent two days in the shop assisting: opening and closing inspection panels, removing portions of the interior, cleaning up the propeller, and degreasing the belly.  The usual stuff.  Plans for 2013 involved replacement of the piano hinges on the cowling, investigating evidence of an exhaust leak near the #1 cylinder, and complying with the recently enacted FAA Airworthiness Directive AD2013-02-13 on the stabilator control system.  This involved opening the conduit running along the center line of the airplane from front to back.  Removing the 2003 upholstery revealed the original factory carpeting from 1979 underneath,  still glued over the access panels.  Removing that nasty stuff was like picking at a three decade old scab (and nearly as fun).

While examining the cowling, it was obvious that the silicone baffle seal material was not sealing as tightly as it should.  We replaced these with larger pieces and subsequent test flights showed a healthy 20°F decrease in cylinder head temperatures across the board!

The exhaust leak, which I initially attributed to a bad gasket, actually resulted from a cracked exhaust pipe.  Jim ordered a replacement and welded it into the existing manifold.

I also replaced the oil return lines on cylinders #1 and #3 that were old and brittle.  In the process, I discovered that the primer line to cylinder #2 was broken.  I always learn something new during these inspections; I did not realize that a primer line ran to #2 - it is completely hidden by engine baffling.

A junior mechanic witnessing my discovery commented, "wow, I've never found anything that Jim missed."

"That's because Jim doesn't miss much," I told him with a heartfelt smile.

Because my engine is mid-time (almost 1000 hours exactly), I wanted to do a borescope analysis to check the condition of the cylinders, the valves, and their seats.  It was my first time using a borescope and Jim did a great job of orienting me to the landscape inside my engine.  I was a little surprised at how clean everything was, the gleaming interior only broken up by a small amount of carbon residue on the faces of the exhaust valves and pistons.  The valves and seats showed no evidence of thermal stress or damage.

"That's what a healthy engine looks like," noted Jim as we finished.  The extra peace of mind is great to have.

While I was otherwise occupied, Jim started draining the oil and I took a sample for metal analysis.  Sometime later, Jim noted that the engine was ready for fresh oil.  As I started pouring the second quart of oil, Jim walked by and said, "you DID close the oil drain before you started that, right?"

I looked and saw that the scrap oil bucket was fuller than it had been previously.  Rats.  When I change my own oil at home, I always close the valve and deal with the used oil before even pulling out the new - so it did not occur to me to check the valve, even though I should have.

Different people, different procedures (I still should have checked).

I retrieved the Warrior on the following Saturday, April 13.  She sported new piano hinges on a repainted cowling and Jim had even managed to remove a nasty oil stain from the passenger side carpet, which was a nice touch.  I gave the airplane a thorough preflight in the maintenance hangar before pushing out into the elements.  When I departed on runway 28, the AWOS was calling wind out of 260° at 17 knots gusting to 30.  It was a bumpy ride home.  On final approach to Le Roy, the wind was 12 knots gusting to 30, leading me to account for a hefty gust factor while landing.

Squeak (upwind wheel), squeak (downwind wheel)...just as nice as anyone could ask for.

When I turned the airplane broadside to the wind and shut down, my propeller stopped in a different position than usual, but I have seen this happen before in strong winds and did not give it much thought.

The next time I flew, on a lovely calm day, I discovered significant vibration at mid-range RPM and, upon shutdown, the propeller stopped in the same unusual position. I called Jim and suggested that my prop was not properly indexed.  Considering that he had done a dynamic balance on the powerplant two years before, it seemed a shame to undo all that work.

On the next nice flying day, they worked me into their schedule to make it right.  With the strong vibration at approach RPM, I had a wonderful excuse to do a power-off 180° landing from the pattern. At pattern altitude over Genesee County, the incredibly clear air yielded a vision of the Buffalo, Niagara Falls, and Toronto skylines beyond my windscreen plexiglass. The latter city was over 70 nautical miles away.

My diagnosis was correct; although spinner and propeller were indexed to the bulkhead, the bulkhead was not properly indexed to the crankshaft. We scratched our heads over how this happened.  When Jim and I reinstalled the propeller, the bulkhead was already placed onto the crank by another mechanic that had been assisting Jim.  He had not oriented the bulkhead to the crankshaft.  Jim and I did not check to see if the bulkhead was properly indexed before aligning everything to it.  A round of apologies were offered, but no real harm was done.

Cruising over Upstate NY on the way to Dansville for a bite to eat, I realized that the propeller indexing issue was exactly like me adding oil to the engine while the drain was still open.  It was a case of too many cooks spoiling the broth.  In both cases, people worked according to their usual practices without accounting for the way others do things.  Either issue could have been prevented with a rigorous "trust, but verify" approach.

The lesson here (or, perhaps, reminder) is that two heads (or more) are not necessarily better than one!

The same applies to two pilots flying together in the same airplane - if responsibilities are not carefully delineated, it is too easy for each to make dangerous assumptions about what the other guy may or may not be doing.

As for me, I'm happy to have my airplane back in tip-top condition and running cool and smooth.

And, having received my invoice, I am also happy that the annual inspection just happens to be scheduled right after my bonus payout each year!


  1. Chris,
    It sounds like a very thorough annual. Every year there are issue we must attend to, we just hope they aren’t too expensive. Great catch on the prop indexing, I’ll have to read more about that or ask the guys at the shop to explain it to me in detail.

    What a difference the new baffles make! Noticeable change on the Sundowner too, cooling is the key to keeping our powerplants healthy. Glad to see you’re back flying, 08Romeo is still in the avionics shop.

    1. I think they usually are thorough - they do a good job. In my case, the prop/engine were dynamically balanced in 2010, which occurs by adding weights to the bulkhead (similar to a tire). At this point, the bulkhead is no longer symmetrical (if it ever was), so everything needs to go back together in the same relative position.

      I've been complaining that my CHTs run on the high side, but the baffles appeared to be in good shape. By now, however, wear on the baffles made those portions that did not seal well obvious.

      I'm sure the upgrades will make the time 08R spent in the shop wholly worthwhile, Gary.

  2. As a renter, I've heard exactly zero about indexing before - great little lesson for me there. Glad it was a relatively easy fix!

    As to the oil filling, I think that's just the airplane owner's version of a transmission flush, right? :)

    1. Oh, yeah, I totally meant to do that! :-)

      As far as putting the prop on correctly, look up dynamic balancing sometime. The point is to check the balance of the engine/prop combination. If any imbalance is corrected by weights, then they need to be properly positioned relative to the entire system being balanced: both the prop and the crank.

    2. Certainly makes sense given the forces at play. After all, I know prop tips can go supersonic. Thanks for the impromptu lesson!

    3. Hah! Not on our airplanes (we would need really long props for that). Now the prop tips on a T-6,on the other hand, those come close (hence the distinctive growl).