I was reading many of the responses to the question about TTAF that had been posed.
There is a fellow at our airport who has a former pipeline patrol Cessna 182 with about 17,000 hours on the airframe.
The utility company that owned it previously began to get a little concerned with the fatigue life of the wings when the airplane hit 10,000 TT.
The story goes that they contacted Cessna and asked what the design life of the wings is.
Supposedly, when they told the Cessna engineer that the airplane had been used for low level patrol work all of its life, and that it had spent those 10,000 hours in the low-level turbulence, the Cessna guy got scared - real scared. They were advised to replace the wings.
They did, and the airplane is now in private hands and enjoying more high level cruising flight, but still has 7,000 hours on the new wings.
No amount of maint. will delay or dispell fatigue problems, unless you can see the beginnings of cracks everywhere along the wing, inside and out, for every little bit of the entire wing; which you can't. I suppose that the wings could be x-rayed, like Beech 18 spars are, but that's not a practical solution.
High time airframes
Moderators: GAHorn, Karl Towle, Bruce Fenstermacher
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eichenberger
- Posts: 51
- Joined: Mon Sep 09, 2002 8:27 pm
Anecdotal evidence such as this is not worthy of repetition in my view. Certification requires that aircraft components be either "life limited" (which our Cessnas are not), fail safe, or "on condition" which means there must be a proscribed inspection program. The only proscribed inspections for our Cessnas are visual, and there has never been an inflight failure of a strut-braced Cessna wing. Not even among some that have been horribly neglected.
But I'm sure Cessna will be happy to sell you anything they have in stock.
But I'm sure Cessna will be happy to sell you anything they have in stock.
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eichenberger
- Posts: 51
- Joined: Mon Sep 09, 2002 8:27 pm
I'm not too prideful to admit error, but I'd like to be shown the accident report on the accident "down south" or any other that found the cause of the accident to be inherent structural failure of a strut-braced Cessna wing.
I'm not referring to where someone went past red-line in a spiral and then pulled the tail off in a banked pull-up, that resulted in a pile of sheet metal in a smoking hole somewhere. I'm not talking about the 180 in Mexico that lost it's wing because it was screwed onto the fuselage with ordinary hardware-store bolts. I'm talking about an aiplane that properly assembled, storm-related or not, was caused by the failure of wing structure.
I read every accident report I can get my hands on, and my belief is that's never happened.
I'm not referring to where someone went past red-line in a spiral and then pulled the tail off in a banked pull-up, that resulted in a pile of sheet metal in a smoking hole somewhere. I'm not talking about the 180 in Mexico that lost it's wing because it was screwed onto the fuselage with ordinary hardware-store bolts. I'm talking about an aiplane that properly assembled, storm-related or not, was caused by the failure of wing structure.
I read every accident report I can get my hands on, and my belief is that's never happened.
>> there has never been an inflight failure of a strut-braced Cessna wing.
George, maybe this one fits your criteria, a 185 in Alaska, 3 years ago:
http://www.ntsb.gov/ntsb/brief.asp?ev_i ... 1135&key=1
"Evidence indicated the airplane broke apart in-flight."
George, maybe this one fits your criteria, a 185 in Alaska, 3 years ago:
http://www.ntsb.gov/ntsb/brief.asp?ev_i ... 1135&key=1
"Evidence indicated the airplane broke apart in-flight."
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rudymantel
- Posts: 451
- Joined: Sat Nov 23, 2002 4:03 pm
I just checked that NTSB site and the right wing separated from the fuselage of the 172 on 11/29/02. However, the preliminary report stated that the right wing's strut to fuselage fitting was found without a nut that secures the fitting to the fuselage. Hmmm- might that have had something to do with the failure ?
(Our 170's are built differently from the 172- On the B model the bolt securing the strut to the fuselage goes through the landing gear box fitting in the front and through a series of doublers and two spacers at the rear.
The spacers are tied to either side of a bulkhead and doublers by three blots and nuts. )
Rudy
(Our 170's are built differently from the 172- On the B model the bolt securing the strut to the fuselage goes through the landing gear box fitting in the front and through a series of doublers and two spacers at the rear.
The spacers are tied to either side of a bulkhead and doublers by three blots and nuts. )
Rudy
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eichenberger
- Posts: 51
- Joined: Mon Sep 09, 2002 8:27 pm
To me there is no doubt that strut braced Cessnas are strong. Given the fact that the 172 is the all-time most popular airplane ever built, and with the abuse that many have received during their lives, the fact that they stay together is obvious.
I intended, in my first post to this thread, to simply relate what Cessna had to say to one person.
Of course, Cessna likes to sell parts, and their position may be influenced by that. However, in my experience, most engineers aren't marketing people, and the engineering side of most all manufacturers isn't so swayed by financial considerations.
Thanks to Rudy - I didn't realize the differences in the strut mounting hardware bewtween a 170B and a 172.
I intended, in my first post to this thread, to simply relate what Cessna had to say to one person.
Of course, Cessna likes to sell parts, and their position may be influenced by that. However, in my experience, most engineers aren't marketing people, and the engineering side of most all manufacturers isn't so swayed by financial considerations.
Thanks to Rudy - I didn't realize the differences in the strut mounting hardware bewtween a 170B and a 172.
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rudymantel
- Posts: 451
- Joined: Sat Nov 23, 2002 4:03 pm
The pipeline aircraft suffered a failure due to improper maintenance. (It was assembled incorrectly at the lift strut.) It also was not a particularly high-time airplane having only about 7,000 hours or so.
The Alaska airplane is an interesting study. I remember that one and if I recall correctly there were several issues involved. One, (Cessna's view) is that the airplane was incorrectly and (unapproved by them) improperly modified with a STOL mod that radically changed the flight control system and altered the stall characteristics of the aircraft to the point of detriment to the manuevering speed. Two, the pilot was suspected of attempting to extend flaps in order to create drag to counter severe vertical accelerations in a thunderstorm. Cessna legal dept. was careful to point out that the aircraft is not designed to handle negative G's with flaps extended, and the wreckage indicated that negative G's was a contributing factor to the accident. They also pointed out that the extension of flaps, due to the (Cessna) unapproved STOL modifications, simultaneously extended/drooped the ailerons which increased flight load factors on the wing.
I realize that Cessna is likely to have all sorts of legal argument to belay liabilities, but I believe they had a plausible claim that the wing, having been modified to decrease stall speeds, suffered from increased flight loads imposed by turbulence that an unmodified aircraft would not have experienced. This was further complicated by improper operation of flaps, a fact that further weakened the non-original design. (I'm not sure that the severity of those storms wouldn't have destroyed a battleship if it were airborne, however. I'm not trying to claim that Cessna's are T-storm proof. I just have a lot of faith in the strut-braced design to deal with high flight times when properly maintained. Twenty-thousand hours are no strain on a strut-braced Cessna. I'd be willing to fly one that had 50,000 hours if it were corrosion free and was not improperly repaired or modified.)
The Alaska airplane is an interesting study. I remember that one and if I recall correctly there were several issues involved. One, (Cessna's view) is that the airplane was incorrectly and (unapproved by them) improperly modified with a STOL mod that radically changed the flight control system and altered the stall characteristics of the aircraft to the point of detriment to the manuevering speed. Two, the pilot was suspected of attempting to extend flaps in order to create drag to counter severe vertical accelerations in a thunderstorm. Cessna legal dept. was careful to point out that the aircraft is not designed to handle negative G's with flaps extended, and the wreckage indicated that negative G's was a contributing factor to the accident. They also pointed out that the extension of flaps, due to the (Cessna) unapproved STOL modifications, simultaneously extended/drooped the ailerons which increased flight load factors on the wing.
I realize that Cessna is likely to have all sorts of legal argument to belay liabilities, but I believe they had a plausible claim that the wing, having been modified to decrease stall speeds, suffered from increased flight loads imposed by turbulence that an unmodified aircraft would not have experienced. This was further complicated by improper operation of flaps, a fact that further weakened the non-original design. (I'm not sure that the severity of those storms wouldn't have destroyed a battleship if it were airborne, however. I'm not trying to claim that Cessna's are T-storm proof. I just have a lot of faith in the strut-braced design to deal with high flight times when properly maintained. Twenty-thousand hours are no strain on a strut-braced Cessna. I'd be willing to fly one that had 50,000 hours if it were corrosion free and was not improperly repaired or modified.)
A local Flying service tore down their C-185 for rebuild at 10,000 hours due to fatigue cracks in the upper wing skin.The local A&P IA says it is not uncommon to see fatigue cracks in wing skins of cessna aircraft with 10,000 hours. Not likely to fall out of the sky but something to watch for with those kind of hours.
Yep, in the early '70's I flew for a subcontractor pipeline patrol and we had inherited a 140A from Humble Oil and Refining (Exxon). It had 23,000 when we got it, and I put another 1,000 or so on it. It may have had it's outer wing panels re-skinned due to cracks from low-level stresses. (They oil-can some in flight.)
Beech has a special purpose inspection for aircraft with more than average time spent below 10,000 feet.
They've got to be inspected and maintained, for sure.
Beech has a special purpose inspection for aircraft with more than average time spent below 10,000 feet.
They've got to be inspected and maintained, for sure.
George, where did you come up with that additional info on the 185 breakup (eg. Cessna's point of view)? I don't think I ever saw anything more that the official NTSB report.
fwiw, there is a 180 in Ketchican with well over 20,000 hrs on it and still doing fine. What's more amazing is that almost all of those hours are on floats, in salt water!
fwiw, there is a 180 in Ketchican with well over 20,000 hrs on it and still doing fine. What's more amazing is that almost all of those hours are on floats, in salt water!
A local attorney friend, also a pilot, subscribes to several journals including an aviation law review, and sends excerpts to me that he thinks I'd find of interest.
(I used to receive copies of several pubs including NTSB Reporter and Aviation Law Review when I was chief pilot of an AMEX subsidiary. Our legal department would forward memo's and excerpts to me they thought I'd find of interest. (I used to post them on the local airport bulletin board until we got accused of copyright infringements.) Anyway, if you are really interested in such things and have deep pockets you might think about buying a subscription. But be forewarned,...they are in it for the money. They're not cheap.
(I used to receive copies of several pubs including NTSB Reporter and Aviation Law Review when I was chief pilot of an AMEX subsidiary. Our legal department would forward memo's and excerpts to me they thought I'd find of interest. (I used to post them on the local airport bulletin board until we got accused of copyright infringements.) Anyway, if you are really interested in such things and have deep pockets you might think about buying a subscription. But be forewarned,...they are in it for the money. They're not cheap.
In the June, 2003 issue of the Cessna Pilot's Assoc. magazine, Vol 20, No 6, page 6739, Tech Topics, there is an article on purchasing older airplanes. In part, under "High Time Airframes" the author (Mike Busch) writes:
"Very high-time airframes are another matter, however. We used to think that Cessna airframes would pretty much last forever if adequately protected from corrosion. That may still turn out to be true for the strut-braced singles, but in recent years there has been increasing concern over the useful fatigue life of cantilever-wing airframes,..."
Cantilever wings depend highly upon wing spar cap integrity for their strength. That cap is not easily inspected or repaired should it be found cracked. In fact, just discovering the crack can be a problem with such designs.
The strut braced wing is very different in it's flight load paths and has much less stress placed on it. In fact, the all-metal wing has the single-strut because the ribs and skin form a torque-box that resists twisting. The earlier rag-wing, like most ragwings, have dual lift struts because the internal wing structure cannot resist strong twisting moments during overload conditions. The STOL kit that was installed on the Alaska-crash C185 actually increased wing-twisting moments beyond that originally planned for in the design, due to the "drooping" of ailerons when flaps are extended, even fractionally. The combination of loss of negative-G strength in the original wing design when flaps are extended, coupled with the further twisting moments imparted by the STOL kit that the drooped flight controls caused (neither intended nor planned for in the original Cessna design, and at least partially resulting in the STOL modification not being approved by them) contributed to the twisting failure of that wing when the pilot was believed to have improperly applied flaps while in severe up/down drafts in that storm front. (Did he incorrectly think that applying flaps would create sufficient drag to slow the airplane down, thereby improving it's chances of surviving severe turbulence?)
From the accident report: "The wing spar had forward twisting at the bottom of the vertical spar web at the wing lift strut fitting. The wing aileron connect/droop push-pull tube had upward bending and was separated from the aileron bell crank."
The STOL mod and it's drooped trailing-edge devices may have increased twisting on that wing. In any case, Cessna almost never approves aftermarket mods to their airplanes for reasons such as this.
I don't mean to "monday-nite quarterback" that poor pilot's presumed actions. (And he probably thought (incorrectly in my opinion) the STOL mod, having been STC'd, would not be a structural problem.) I'm just hopeful that more folks will realize that modifying these airplanes is not always an improvement in all ways, and that proper operation of the airplane is important in unusual conditions. (Keep those flaps retracted in turbulence, and don't chase altitude. Just keep it right-side up and pointed straight ahead and below 115 mph/100 kts. You'll be out of it in a mile or so.) Just another one of my goofy opinions derived over almost 4 decades of discovering myself still alive after some pretty interesting unintentional encounters with mother nature.
"Very high-time airframes are another matter, however. We used to think that Cessna airframes would pretty much last forever if adequately protected from corrosion. That may still turn out to be true for the strut-braced singles, but in recent years there has been increasing concern over the useful fatigue life of cantilever-wing airframes,..."
Cantilever wings depend highly upon wing spar cap integrity for their strength. That cap is not easily inspected or repaired should it be found cracked. In fact, just discovering the crack can be a problem with such designs.
The strut braced wing is very different in it's flight load paths and has much less stress placed on it. In fact, the all-metal wing has the single-strut because the ribs and skin form a torque-box that resists twisting. The earlier rag-wing, like most ragwings, have dual lift struts because the internal wing structure cannot resist strong twisting moments during overload conditions. The STOL kit that was installed on the Alaska-crash C185 actually increased wing-twisting moments beyond that originally planned for in the design, due to the "drooping" of ailerons when flaps are extended, even fractionally. The combination of loss of negative-G strength in the original wing design when flaps are extended, coupled with the further twisting moments imparted by the STOL kit that the drooped flight controls caused (neither intended nor planned for in the original Cessna design, and at least partially resulting in the STOL modification not being approved by them) contributed to the twisting failure of that wing when the pilot was believed to have improperly applied flaps while in severe up/down drafts in that storm front. (Did he incorrectly think that applying flaps would create sufficient drag to slow the airplane down, thereby improving it's chances of surviving severe turbulence?)
From the accident report: "The wing spar had forward twisting at the bottom of the vertical spar web at the wing lift strut fitting. The wing aileron connect/droop push-pull tube had upward bending and was separated from the aileron bell crank."
The STOL mod and it's drooped trailing-edge devices may have increased twisting on that wing. In any case, Cessna almost never approves aftermarket mods to their airplanes for reasons such as this.
I don't mean to "monday-nite quarterback" that poor pilot's presumed actions. (And he probably thought (incorrectly in my opinion) the STOL mod, having been STC'd, would not be a structural problem.) I'm just hopeful that more folks will realize that modifying these airplanes is not always an improvement in all ways, and that proper operation of the airplane is important in unusual conditions. (Keep those flaps retracted in turbulence, and don't chase altitude. Just keep it right-side up and pointed straight ahead and below 115 mph/100 kts. You'll be out of it in a mile or so.) Just another one of my goofy opinions derived over almost 4 decades of discovering myself still alive after some pretty interesting unintentional encounters with mother nature.