Cessna Twin Spars

[Sparweb]

Has anybody been following the developments in this impendiing Airworthiness Directive, or, better yet, directly involved?

http://www.cessnatwinssparcorp.org/news.html

http://www.cessnatwinssparcorp.org/pdf/nprm2002ce05ad.pdf

I've been poking into this story for a week now, and I'm still not clear on what's motivating the FAA to impose a Damage Tolerance analysis on an aircraft that wasn't type-certified with that in mind. (So are plenty of Cessna owners.)

In the bigger scheme of things, are DT philosophies suddenly going to be imposed on older aircraft as a broad-brush way to keep them from falling out of the sky? Occasionally, these old war-horses do succumb to fatigue failures, but more often it's the typical pilot/mechanic/inspector/weather/stupidity failure cycle that brings any aircraft down, new or old.

Are there similar rumblings from the FAA against aircraft other than these Cessnas?


Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

 

[crackman]

Steven

Its been a long time since Aloha, but the FAA has finally issued the mother of all damage tolerance rules. The FAA issued the Aging Safety Rule on Dec. 6 2002 which went into effect on Dec. 6 2003. It essentially requires all 121 and 129 operators carrying 9 passengers or more (those under must still have a SID but can be based on fatigue) to have damage tolerance based inspection program and all repairs (past and present) must also be DTA. The fleet impacted by this is very large and includes the Cessna 410. In addition, mandatory audits will be required on a period basis. Here is a link to the Federal Registry with the published rule.

http://a257.g.akamaitech.net/7/257/2422/14mar20010800/edocket.access.gpo.gov/2002/pdf/02-30111.pdf

Much activity on this topic. I am currently part of an industry group (ARAC) tasked with developing the guidelines for the implementation of the program.

As a personal note, I have reviewed the Twin Spars info. I do not believe the analysis is going to help them much in improving the numbers however I do think that they could benefit tremendously by pulling together and developing their own modification at a reduced cost. I think that is where they need to concentrate their efforts. After so many incidents with fatigue, the FAA has all the justification for their rulings and plus the industry has know about it since 1978 (707 Lusaka accident) and really driven home after the 1988 Aloha accident. And more recently the China Airlines crash as a result of a fatigue failure from a repair in 2002.

Here's a link to some info on this latest crash. By the way this crash cited the need for more aging aircraft rules:

http://articles.findarticles.com/p/articles/mi_m0UBT/is_15_17/ai_100405167

Hope this info has helped


James Burd
FAA DER - Structures/Damage Tolerance

 

[Sparweb]

The China Airlines was a disgrace to the maintenance personnel involved - and should not be so to the regulatory authorities, except those who are charged with enforcing existing rules. CI had plenty of opportunities to detect the crack, but deliberately chose not to. No amount of SID's or bulletins from Boeing would have changed that.

I had read parts of that final rule before, but hadn't realized that aircraft with <9 seats would also be affected. (More reading to do, I suppose) It looks like Cessna is 100% on board with the philosophy, because they participated greatly in the research and development of the SID for the 400's, including FEM models and full-scale tests, whereas I have yet to see a competing manufacturer do the same. Perhaps they are, but aren't as public about it. Now that I mention it, though, I do recall seeing an Office of Aging Aircraft Report on testing of Beech 1900's, so maybe there is more happening that I realize.

Help me make the link between an airline in China and the airworthiness rules in the USA: foreign airlines must demonstrate that they comply with FAA part 129 in order to to fly scheduled service to the continental US? Does that mean that the FAA was partly responsible for not noticing the sloppy maintenance practices at China Airlines?



Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

 

[crackman]

I agree wholly with the poor maintenance and its a disgrace that a "temporary" repair was allowed to stay on the aircraft for 22 years.

As for the SSID being able to cover, that is exactly the point. Up to now, none of the OEM SID's address modified structure. All of the PSE inspections are for green aircraft only. In fact, depending on the OEM, some SID PSE inspections only cover a very specific location (even down to 3 or 4 fastener holes). Some of these philosophies assume that the most critical location will crack first and therefore inspecting it will safely cover the remainder of the area. NOT SO. Also, for the pre amendment 45 aircraft with SIDs, there is no FAA requirement at all to even do damage tolerance for anything other than the physical PSE location and most ADs on SIDs dont even mention a requirement for assessing the impact of repairs to PSEs.

Anyways, the fuselage pressure boundary repair assessment rule that went into effect in 2002 (FAR 121.370) has thresholds for doing the assessment. However, depending on the airline, it may or may not have been completed at this point. In fact, note taht the rule went into effect the same year China Airlines crashed. Maybe if it hadnt taken 14 years since Aloha to get the rule passed......

Also, the intent of the fuselage pressure boundary RAP was always intended as just a first step trying to address the structure with the most numerous repairs. Repairs to wing spars, engine mounts and flap tracks are just as critical. It shouldnt take a wing flying off (in the case of the Cessna 410 and the C130A firefighter) to convince people of this.

I have seen several hundred service related fatigue cracks in my years of experience and in almost every case the cracks could certainly have been either detected by DTA based inspections or avoided by placing a life limit on the component. All repairs should be required to meet the same level of safety as the baseline structure. No self respecting DER would ever have approved the China Airlines repair for DTA. Also, from what I know, the repair was only approved as "temporary" (ie time limited) which is only a "recommend approval" for any DER which also means it should have been approved by the cognizant FAA ACO. Unfortunately, prior to this rule, there is little requirements for tracking the status of any permanent or "temporary" repair. That is left up to the operator.

The new rule I believe will be a significant improvement. Other than the DTA requirement, it places a mandatory inspection of all repairs. If anything else, each one will get a very close inspection by an FAA inspector. Remember, many but not all operators still believe "if it aint broke dont fix it". (and if the doubler covers up the damage, oh well) Also, not all repair stations are created equally. So at least this will require a physical inspection. The issue at this moment is how to phase this requirement into the fleet.

Just as a final thought, how long should we really allow aircraft to fly? The answer is - As long as their safety is ensured. Many old aircraft never even had a fatigue test. I dont know about you, but as much as I like B17s, I still wouldnt want one crashing thru my roof.(did you note the AD issued just a couple of years ago by Seattle ACO to all B17 aircraft for mandatory mods to the wings due to chronic fatigue cracking?)

One of the upcoming rules includes establishing a Limit of Validity. Basically this is the equivalent of a 2 lifetime fatigue test divided by a scatter factor of 2. This LOV would limit the operation up to that point until an extended fatigue test or substantial analysis and component testing could be completed to establish a new LOV. Essentially this would ensure a service life up to LOV without widespread fatigue cracking.

As for the link with the US, the FAA considers all accidents in their evaluations. In fact, when an accident occurs overseas but involves a US manufacture aircraft, most of the time the local version of the NTSB will notify and forward all information to the cognizant FAA ACO. And in almost every case, the FAA will contact the OEM and inititate an investigation due to the possible impacts to the US operated fleet. By the way, the JAA/EASA is in the process of adopting a similar version of the FAA Aging Safety rule but even more stringent from what I hear.

James Burd

 

[Sparweb]

Since the UK already established life limits on imported aircraft of US manufacture long ago, it would be no surprise to see the JAA drawing its own line in the sand.

Speaking of international authorities, I realize that it would be worthwhile to find out if Transport Canada is going to rubber-stamp the FAA AD on the Cessnas when it comes out. And whether they are pursuing similar objectives on some Canadian TC'd aircraft.


Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

 

[aviat]

Looks like the AD has been canceled!

http://www.ramaircraft.com/Wing-Spar-Information/Wing-Spar-Information.htm

 

[Sparweb]

I had the feeling all along that it was the lawyers at Cessna pedalling the hardest...

In time we'll learn why the FAA has chosen to do as they have and then we will see if more will come of this - in regards to Cessnas, or other manufacturers.


Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

 

[aviat]

Steven
Avweb has a new story on their eletter on an emergency AD on cessna 402C and 414A spars

http://www.avweb.com/eletter/archives/avflash/356-full.html#189227