Over the past two years we have seen a remarkable surge in orders for single aisle airplanes. Much of this has been driven by fuel prices. But there has also been an issue bubbling under – airplanes in many fleets are getting older.
Pat Duggins (http://www.patduggins.com/) is an expert on aging airplanes and spent some time explaining the issues. You might be surprised what you learn from this.
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Has to make you wonder about startups with 737-400s. I name no names.
Very interesting take. Still, Helios was a really different cause. I am not second guessing Mr Duggings (hell I am not even in the industry) if (*if*) he implies it was in it’s root a design issue of the 737 with too much grandfathering certificates. But the “direct” root if I can call it that way, was a wrong switch setting, read not doing the proper checklists. It had absolutely nothing to do with riveting up the side of the 737. But it might have with his basic take on aging design.
Oh no… I am shocked to bits after listening to this podcast.
This grandfathering right must be stopped.
I can only hope that the ongoing case http://aje.me/s3Xq4C for the NG’s is completely out of order, otherwise this can only contribute to more horrible news.
The plot thickens… watching againg the al jazeera documentary on the allegations over the NG, Pat Duggins is actually featured in it! There is also plenty of info in the web around similar issues with his name involved. Is this the same person?
When the 737 was designed, Boeing was able to benefit from the lessons learned from the Comet catastrophes. On the original design of the Comet, if a crack started to develop there was nothing to stop it from propagating. On all subsequent designs they introduced a new technique of assembly that would prevent any crack developing from spreading too much. It would be contained and stay localized.
In the case of the Aloha Airlines incident this measure was not effective in preventing the tear-up of the skin because there were too many areas that were developing cracks simultaneously. It was not a case of one crack propagating out of control, like in the case of the Comet for example, but a bunch of cracks “looking for each other”. When the time was ripe they all gave in unison.
In regards to the Helios Airways crash, the airplane did not depressurize in flight. As a matter of fact it was never pressurized at all. The airplane took off with the pressurization system selected to “manual” for ground operation. Or said another way, the pressurization of the airplane did not come on automatically like it normally does, because the selector switch was not on “automatic” for flight operation.
Before the flight the airplane had gone through a maintenance routine to check the pressurization system, and to accomplish the task the selector had to be positioned to “manual”. Normally the technician is supposed to put the selector back to “automatic” for flight operation. But this was not done, and the pilots never checked it either.
So as the airplane reached altitude the pilots fell asleep because their airplane was not pressurized. Actually, all onboard fell asleep except for one flight attendant “would be pilot” who had done an oxygen mask. He survived until he used up the last bottle of oxygen. And the airplane itself stayed in the air until it ran out of fuel.
Following the accident there was an inquiry that lasted seven years. In the end the maintenance engineer (technician) was sentenced to ten years of prison because he had left the selector switch to “manual”. The maintenance procedure calls for putting the selector switch back to “automatic” after the check is done.
Today the crew would be warned by an alarm if they attempted to take-off with the airplane pressurization system in “manual” mode.
One of the things said in this podcast is that the new airplanes are tested for fatigue. I’m just wondering then, why the wing cracks on the A380 were not discovered during testing. It is somehow by coincidence when investigating the wings of the Qantas A380 with the engine blow-up that the cracks were discovered, Any ideas?
Comet: Realization that fatigue is a big issue in aluminum aircraft
Aloha Airlines: Realization that corrosion fatigue is worse than just fatigue: the birth of the term ‘aging aircraft’; long term, a big driver to composites as on the 787 and 350.
Helios crash: nothing to do with explosive decompression. Eg see http://en.wikipedia.org/wiki/Helios_Airways_Flight_522
Southwest: best I know, two sudden decompression incidents: one in 2009, one in 2011. 2009 attributed to production problems best i remember, 2011 attributed to inspection problems, hence FAA emergency AD.
I am not aware of any other sudden decompression incidents. Am happy to be corrected.
Is this a design problem? By definition everything is a design problem, as you can always make it stronger and better to avoid a failure. But that misses the point: aircraft design is intended to incorporate inspections (with redundancy to catch errors) into the process of catching the damage before it becomes critical. In both cases of sudden decompression, unforeseen errors lead to a critical event which was still NOT catastrophic, in other words the design was damage tolerant as it should have been!
Personally, I found the credibility of the speaker to be severely diminished when he used the Helios incident as an example.
Who is Pat Duggins and what is his goal?
He said Boeing changed the “737 crown” thickness on the Classic, but then said, “they didn’t change the pressure vessel.” Isn’t that “crown” part of the “pressure vessel?” He said, they, “put a 16 foot long doubler,” on the fuselage. Isn’t that part of the “pressure vessel?”
“How many incidents have we had since the SouthWest decompression issue?” “I don’t know.”
He goes on and one about how planes are showing up in the bone yards because airlines can’t afford to fix them any more. Isn’t that normal? And, of course, we see airlines scrap old planes for new just for fuel efficiency and nothing more.
So, it seems this guy is not an much of an aviation expert. It seems like he’s a self anointed expert trying to use this “pressure vessel” and normal airframe fatigue as a way to promote himself from blue collar mechanic to white collar consultant.
Of course, how many 737 Classics are flying around the western world for us to worry? And, since he admits “flying is safer than driving a car,” what’s the point?
If he was a member of, say, the NTSB for years and years, I’d believe him. I don’t.
Structure cracking on A380 was secondary so there was no need for specific inspections even if cracking occurred during the tests.
Immediate attention is usually directed to Principal Structural elements (PSEs) or your primary structure. Since the elements that cracked are not part of the primary structure priority was, most probably, given to the structure that was defined to be primary.