Cessna 172S in-flight breakup

Cessna 172S in-flight breakup

Hmmm...
http://www.ntsb.gov/ntsb/brief2.asp?ev_ … amp;akey=1

describes a 172S which broke up in flight March 21, 2003.  I haven't been able to find any articles or narrative on this except through the NTSB.  Two eyewitnesses saw the in-flight break up of this aircraft, tail number N219ME, from Elite Flight Center in Georgia.

This seems like it would be more interesting.  With many thousands of 172s and millions of flight hours over 50+ years, through thunderstorms, illegal amatuer aerobatics, hard landings, etc. this is the first reported in-flight airframe breakup of a 172 I have ever read (and it's one of the "new Cessna" models, right?  Not a 20+ year old 172).  Isn't the 172S one of the ones with the infamous, exhaustive 13 sumps? 

This seems like an extremely newsworthy item, but I haven't seen COO or CPA articles on this.  Can someone point me to any news on this?  In terms of general aviation accidents of airplanes with standard airworthiness certificates, this is the most surprising report I have ever read (given the awesomely robust history of the 172).  Sure, if this was a Bellanca or a 35, I'd hardly blink, but a 172?

Anyone have any references to followups?  Did Cessna ever have any comment?  I would imagine a lawsuit was filed...

Mark Boyd

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Re: Cessna 172S in-flight breakup

By the way, in my initial post I put the initials for the
C e s s n a   P i l o t s  A s s o c i a t i o n and the
newsgroup posting program translated it in an
unexpected way. 

I meant this as a serious post, and I want to make clear
that I am interested in honest and helpful feedback
from any source.

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Re: Cessna 172S in-flight breakup

Mark, the NTSB write-up is unusually comprehensive and cites two witnesses who say the airplane was in a steep nose down attitude (45 - 90 degrees) and building airspeed.  While the report doesn't draw any conclusions as to why the airplane was in such an unusual attitude, it doesn't take very long for any airplane - even one as draggy as a 172 - to build up airspeed, exceed Vne, and overstress the structure when in such a dive.  The report indicates observation of features in some of the structure consistent with stress fractures.

For such a comprehensive report, it's notable that no "Probable Cause" is included.

It'll be interesting to see if the families of the instructor and/or student attempt some sort of defective product litigation against Cessna, and if so how they assert a defective product and deflect responsibility from pilot error.

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Re: Cessna 172S in-flight breakup

I couldn't tell from the report if the NTSB thought the stress was from negative G's (meaning a dive may have caused an overstress) or from positive G's (and perhaps the dive was the RESULT of a partial separation, rather than the cause).  Did the strut fold from positive or negative G's?  Did the wing break first or the strut attach point?  I'm not really expert enough to tell from the report the implications...

Even if it is a negative G overstress (beyond the limits of the airframe), the fact that breakup has never happened before in the millions of flight hours is still quite surprising to me...

The most interesting part really is the lack of publicity or comment on this...

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Re: Cessna 172S in-flight breakup

I couldn't tell either from reading the report. Positive Gs exceeding the structural load limit of the airframe could have resulted if they were much over Vne and tried to pull out of the dive.

It's not unusual for GA accidents, regardless of the cause, to escape widespread publicity until the lawsuits get filed.  That usually takes several months or even years.

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Re: Cessna 172S in-flight breakup

FWIW, on another website, an Atlanta-based pilot posted that he had heard second hand from a local A&P mechanic that a fuel truck had struck and damaged one of the wing struts, and that there was an improper repair when the strut was replaced.

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Re: Cessna 172S in-flight breakup

Stan,

  I am very interested in the specifics of that.  Please either post or e-mail me the website info.

Mark Boyd

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Re: Cessna 172S in-flight breakup

mark boyd wrote:

By the way, in my initial post I put the initials for the
C e s s n a P i l o t s A s s o c i a t i o n and the
newsgroup posting program translated it in an
unexpected way.

I meant this as a serious post, and I want to make clear
that I am interested in honest and helpful feedback
from any source.


Mark,
The COG webmaster configs anything that has to do with the CPA in the CPA--See it did it automatically!  It is nice that we belong to an organization that doesn't do such things with their website.

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Re: Cessna 172S in-flight breakup

Just speaking as to why there is no probable cause statement - I would guess it is waiting for the Board to rule on it.  If you look at the other mishaps that occured that month most of them are still in prelim mode.  The ones that are final are non-fatals.  They always release the factual report before they release probable cause.

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Re: Cessna 172S in-flight breakup

I checked the 172SP we just put on line at the Santa Cruz Flying Club and it is a 2000 model SN 172S8646, N717SP.  The breakup was a 2000 model SN 172S8478, 172S.  At least they aren't real close serial numbers!  But they are the same year, so I'm looking forward to the final report.

The report seems to indicate the bolts attaching strut/wing and strut/lower airframe were present and attached.  As for using the wrong bolt or not putting a nut on it, again, the bolt itself doesn't seem to be the failure point since the strut was still attached.  Granted a loose bolt or wrong installation might cause an interesting twisting or vibration or torque, but it seems the bolt itself was not the separating failure point.

"The right wing separated with a section of the center fuselage bulkhead. The main spar was bent in a downward direction and separated 4 feet outboard of the wing attachment point."

"The right wing strut remained attached to the wing strut attach point and separated at mid span. The fuselage bulkhead structure separated with the remaining section of the lower right wing strut. The fracture surface of both struts exhibited down necking with a 45-degree fracture surface. The aileron control cables were attached to the aileron bell crank. Both aileron and flap cables exhibited evidence of broomstrawing."

I've seen a 172 that was overturned by heavy wind.  The struts were both collapsed mid-span by the negative G of inversion.  An exciting question is whether this happened before or after impact with the ground.  Another exciting question is if negative G's were the cause of the accident or if a structural failure occured before the dive.  The main spar "bent in a downward direction" may be included here as an indicator.  I'm simply not experienced enough to tell if this means before the impact with the ground or after... 

If the plane's right strut really was hit by a truck, and the "repairs" completed during the annual were improper, that would be of course tragic for the two victims, but a relief to me and other 2000 year 172 cessna pilots who are concerned about possible manufacturing defects.

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Re: Cessna 172S in-flight breakup

Don't let the "downward" bend in the spar become a red herring.  Think about how this wing is constructed.  Before it was all-metal, the rag-wing had a double strut configuration, with a forward strut extending upward to the front spar, and the rear strut attaching to the rear spar.  When the wing was redesigned to all metal, the stiff box-sections formed by the ribs resist the twisting stresses created by lift, so a single strut was allowed on the front spar only.
Now consider this:  A very strong positive lift has the effect of applying a twisting motion to the wing lifting at the rear spar.  The only thing preventing it is the stiff box sections of those inter-bay areas formed by the ribs.  But if the wing is overloaded say, in a hard pull up, creating excessive positive G's, that wing will eventually fail with the trailing edge failing upward, forcing the leading edge downward.  That area outboard of the strut attach point will be hit on it's topside by a very strong relative wind, which will cause the wing to fail downward.
  This is the scenario presented by the accident report.  "Necking", or stretching of the spar due to high tension loads, followed by wing failure from a failing wing structure and downward bending of the outer wing panel.

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Re: Cessna 172S in-flight breakup

P.S.- The question I have in my mind regarding this accident, is: How many students and pilots have been stepping on that strut refueling and checking fuel caps?  I believe Cessna made a poor decision to include steps on the strut, which lead pilots to believe that is an OK practice.  It's not.

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Re: Cessna 172S in-flight breakup

I have the refueler trained to use the ladder when I'm watching.........If I take off the step he'll probably put his boot on the strut.

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Re: Cessna 172S in-flight breakup

Thank you to all of the posters who have given their thoughts to the post.  This has been VERY interesting, as usual.

Mark Boyd

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Re: Cessna 172S in-flight breakup

Help me understand the prohibition on stepping on the strut to check for fuel & that the fuel cap is secure.

I usually use a step ladder but have occasionaly been caught without a ladder and used the strut.

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Re: Cessna 172S in-flight breakup

The wing strut is designed to support the wing primarily in tension.  It also offers some small support in compression.  It is strongest in tension like most metals) and weakest in compression.  While on the ground it is supporting the wing in compression.  Stepping on the strut places a side-ways burden on the strut and it's end-fittings that it was not designed to accept.  Repeated abuse from using it as a step  is like repeatedly bending the paper-clip, except in a more insidious manner since aluminum does not need to actually bend in order to receive and store stress.  Subsequent in-flight loads and turbulence will also place alternating tension/compression loads on that weakened strut.
  You can project in your own mind what that does to it's life limit.
(How many have ever taken a long (48" or greater) straight-edge to their struts?  You'd be amazed at how many show light (air-space) along their upper surfaces, caused by bending from using the strut as a fueling step.  And just because it isn't actually bent, doesn't mean it hasn't been stressed.)
  If you do step on it, only do so at it's juncture with the lower fuselage, and only do so in order to steady yourself, ...not to support your weight.  Get a ladder if you need to support weight.

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Re: Cessna 172S in-flight breakup

George,

Thanks.  I agree, it's best to avoid stepping on the strut.

I'm not sure I buy everything you said, technically, but it would be hard to argue without the design of the strut handy.  As far as storing energy in metals, any metal (not just aluminum) in tension or compression is storing energy.  Any you are right you may not observe any deflection.  If you mean residual stress from being bent (cold worked) that would be accompianed by a change in metal properties.   In other words the metal yielded and you have plastic deformation.  That would basically require some repair or replacement for it to be airworthy. 

If most (the center portion) of the strut is tubular in design it would explain a lot and I would be very reluctant to step.  Any denting would make it prone to buckling.   It's odd that cessna would design a step if it is not OK.  The attachment parts to the wing and at the juncture of the fuselage looked solid to me. So I agree if you have to step on it, the juncture with the fuselage is best. 

You stated it wasn't designed for stepping.  I would be surprised if Cessna didn't actually consider stepping forces.  Have you seen the calculations for the design?  It is not unsual in designing structures or attachments to take in consideration abuse by people.  I know of a designs of equipment, like valves, instruments, etc., where the design would consider people in the field as potentially stepping on the equipment.  Nevertheless, you would caution anyone from stepping on the equipment.

Well I'm not sure I feel so good about this anymore.  I have no way of knowing how many peoply may have stepped, jumped and bounce on and off the strut over the last 30 years!

Happy trails......

Seriously though - Thanks again for the info.

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Re: Cessna 172S in-flight breakup

I know with the hundreds of floatplanes around here the strut step is used all the time.

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Re: Cessna 172S in-flight breakup

While the TECNICAL aspect of this in-flight break-up is interesting and worthwhile discussing for all Cessna pilots, it's with quite some mixed feelings that I followed the publicity aspects and hunger for legal consequences in this thread. I hope those same pilots will not complain about the cost of aviation in general and the price of Cessna replacement parts in particular in future threads.

Michel

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