TALESPINNERS - February, 2003

Bugs and Ice
by Bob Porter

Bugs & Ice.  Not two terms that usually go together.  As a matter of fact, when you think of one, the other is probably pretty far removed from your mind.  In the summer when you are cleaning bugs off the plane, the only ice is in your favorite beverage.  In the colder months when ice becomes part of your weekly vocabulary, bugs are in bug heaven or their cocoons or wherever they go when they no longer commit suicide on the leading edge of your aerial chariot’s wings.  But recently, I came across a couple of examples where the two have a common thread, damage.

I recently completed a damage assessment on a Cessna 208B, Caravan.  Let me set the scene for you.  The pilot of the 208 was descending from 10,000 feet into Standiford field at Louisville, Kentucky.  The contract flight, hauling cargo for UPS, had originated in South Carolina and was terminating in Louisville.  Shortly after beginning the descent the pilot heard a “pop.”  A few minutes later he heard another “pop’.  The plane had a slightly different feel to it but nothing that would constitute declaring an emergency.  The controls felt a little different but he couldn’t physically locate any problem.  Looking out the windows, everything looked normal.  The landing went without incident and when the pilot exited the aircraft, he began looking around.  At first, everything appeared normal.  Then he climbed up on the pilot’s door ledge and looked at the top of the wings.  Imagine his surprise when he saw what looked like the Jolly Green Giant had stepped on the tops of the wings.  The right wing was worse than the left.  But the tops of both wings were sucked into the fuel nacelles.  An inspection of the under side of the wing revealed fuel leakage and some slight deformation.

I traveled to Standiford to inspect the aircraft.  I have not seen anything remotely close to the type of damage I saw when I stood on the doorsill and looked down the wings.  Imagine looking down the top of a wing and seeing the top skins sucked down to the bottom skin.  Not a very technical way of putting it, but the visualization is there.  The company who owns the aircraft sent their mechanics to help determine the cause and Cessna was also contacted.  The inspection of the fuel vent system found the debris of a mud-dobbers nest in the main vent line that affects both tanks.  Keep in mind; the caps on these tanks are non-venting. Now the interesting point is that this flight was conducted long after mud-dobbers season.  The plane is normally based at McCollum field in Kennesaw, Georgia (my old stomping grounds).  This plane is a workhorse and flies on a regular basis.  So what happened and why on this flight and not other flights?  A check of the aircraft flight logs revealed that this plane normally flies very short and low altitude flights of less than an hour.  On the flight in question, the plane had been full of fuel, on a long flight at an altitude of 10,000 feet.  As the descent was started into Louisville, the tanks were now low on fuel, the plane was descending from thin air to thick air and the engine fuel pump was working like a machine possessed to keep kerosene going to the burner.  The result, the tanks and fuel structure could not withstand the negative pressure and the wings collapsed.  Aircraft Structures, in Edna, Oklahoma, did the repairs.  The wings suffered extensive spar, rib and skin damage.  The header tank at the pump was also sucked in.  Cost to repair, $123,101.48.  The Cessna technical representative told me that this is the second example of such damage.  The system is designed with a small secondary opening deep in the vent line plumbing in case such blockage occurred near the wing opening.  But in this case, the little buggers climbed past the secondary opening to make the nest.  The owner inspected his fleet and found three more planes with vent blockage.

Don Reasoner keeps very simple plugs in his tank vents while the RV-6 is parked.  They have red flags on them to make sure they are pulled during the preflight.  This is a very good practice to follow any time of the year.  The next time you are on a flight line, notice how many pitot covers you see.  Now think about how many fuel vent line covers you see.  I can keep a plane in the air without the pitot system.  Without fuel, the glide path is predetermined in the POH.

My next example is a little (a lot) less dramatic but frustrating all the same.  It was the day after Thanksgiving and I had a flight scheduled in the company C-182.  The plane is housed at Lebanon-Warren County in a very nice enclosed T-hanger.  As you may recall, it was very cold that day and on the previous Thanksgiving night.  This particular plane has five quick drains in each wing.  The drains are the flush type. I took samples from four of the drains on the left wing with no problem.  As I took a sample from the fifth drain on the trailing edge near the fuselage, I felt a slight crunch when I pushed the sampler into the drain.  After I removed the sampler, the fuel just kept on coming in a steady drip.  Nothing I did would make it stop.  I tried pushing up and down with the sample to see if I could get the drain to reset.  Fuel just kept dripping.  I shook the wing.  I pulled the fuel cap off.  Fuel just kept coming.  I tried the sampler again.  More fuel.  Since it was the day after Thanksgiving and before 8:00 AM, no one was around the airport.  By now the puddle was getting pretty big on the hanger floor and I had 45 more gallons to go.

I pulled the plane out of the hanger and started the engine.  My thought was that maybe the vibration of the plane would help reset the drain.  I was convinced it had dirt wedged in the seat and was stuck.  I needed to go over to Highland County and I was hoping that mechanic would be in.  As I landed at HOC and taxied up to the hanger, I noticed the drain was still dripping.  Damn, more fuel.  The mechanic was in and he took a quick look and said he had another drain.  Another gentleman in the office overheard my conversation.  He heard me say that I felt a crunch when I pushed the sampler in the drain.  He asked the mechanic to get his air hose out with the blow nozzle attached.  He came out to the plane and told me to take the cap off.  He put the blow nozzle to the drain and gave it two or three quick burst.  The fuel stopped immediately.  The problem. Evidently there was a little slug of ice in the fuel that had formed around this drain since it is the lowest in the wing.  When I pushed the sampler in moving the seat up, the ice moved in under the seat causing the crunch I felt.  Interestingly enough, I have never seen even a hint of water in any of the samples I have taken from either wing.  Whether it was just coincidence that this particular load of fuel had some water I don’t know.  I have not seen any water since.  Bugs and ice.  Both can be a nuisance.  Either one can cause a lot of damage given the right circumstance.

Copyright © 2003 by Bob Porter.  All rights reserved.

More Photos from the January Fly-Out

Definitely looks like winter in Ohio!

Canadian Trainer?

The lunch crowd was small this month.

All photos by Bob Porter.