What are the chances of a structural failure in a GA aircraft?

[rickair7777]

The Zodiac aircraft is a perfect example. A kit aircraft, built perfectly by the manual, and yet, there have been many fatal accidents with an inflight breakup. The aircraft wing flutters, and undampened, leads to vibrations that fail the wing inflight. This is an engineering flaw of the airplane, and a recommendation has been put out to ground these until the problem is fixed.

I was assuming that the design was good...undamped resonance can destroy anything from airplanes to rockets to bridges and buildings.

 

[avbug]

Structural failure is a broad term.

I've seen spars crack, but I've seen the step snap off behind a wing, too. Both are structural failures...to which one do you refer?

I have no idea what the "chance" is that it will happen, but rest assured that it does, and will happen. Perhaps to you, perhaps not, but it does happen.

Numerous airplanes require airworthiness directives to replace or inspect spar caps. Few of them have been exposed to undue stress. I've seen cracks occur on a number of aircraft which weren't exposed to aerobatics or severe turbulence, but which cracked none the less.

Some years ago I maintained a fleet of 200 series Cesssnas. I found the vertical stabilizer attach brackets and points cracked, on every single airplane. The failed parts were aluminum, and after investigating the issue, the parts were re-fabricated in steel...which is how you'll find nearly all of them today. The cause of the cracking? Most likely pilots performing slips. Same thing they'd always been taught was safe...and is a lot harder on a structure than most realize. Never the less, a simple, standard general aviation technique.

Cracks and failues can result from overtightening a fitting (airplanes have lost wings that way), undertightening a fitting, using the wrong size bolt (saw a landing gear fail that way), from vibration, corrosion, metallurgical imperfections, and a host of other reasons. Two airplanes I used to fly both lost wings in flight, killing all on board. A large transport I used to fly experienced cracking throughout many of it's primary structural members. Two other light airplanes I flew had cracked spars, discovered by inspection...one completely cracked through in three places.

I couldn't tell you about the "chance," but that mechanical things will break, and parts fail; this isn't news.

 

[imacdog]

The Zodiac aircraft is a perfect example. A kit aircraft, built perfectly by the manual, and yet, there have been many fatal accidents with an inflight breakup. The aircraft wing flutters, and undampened, leads to vibrations that fail the wing inflight. This is an engineering flaw of the airplane, and a recommendation has been put out to ground these until the problem is fixed.

I thought a number of those failures had to do with the aileron cables not being rigged to the right tension? Still, it is not good to have the results that this plane has had.