Life Limits

[Denver98]

My first jet was a TWA DC-9-30 built in the late ‘50s.  The check airman showed me the history of the airplane, it had 110,000 hours and 115,000 cycles on it.  Nevertheless, I was very excited to fly it.    As far as Douglas was concerned, if you can maintain it, you can fly it.  

[GeeBee]

Yep old Donald Douglas built them tough. The 707 was done at 75K, DC-8 had no life limit.

 

[Hector]

Interesting point GB...
For composite plane parts... the inspection technology would need to ‘see’ through the materials... to make sure the fibers are still attached to the composite’s matrix...
There are probably some weaker or more critical sections that would need this type of X-ray (?) vision...
Similar to looking for mini stretch marks that may not be showing at the surface...
PP thoughts only, not a mechanic...
Best regards,
-a-

We use MAUS ultrasonics scan to inspect F/A-18 wings skins (composite) for voids, disbonds, delaminations. It is not unusual to find some voids or small areas of delamination but these can be tracked to see if they grow. Inspections can be put in place to ensure safety. Cirrus could, if they want to, institute a fleet leader program at some point through their dealer network whereby they inspect high time aircraft to see how well the composite structure is aging and use the data to extend the life limit.


Sent from my iPad using Tapatalk

[GeeBee]

Military aircraft are completely different risk models. One, you have depot level trained maintenance, IOW you have someone on the end of that scanner who has standardized training. Two, you have little in the way of liability and if there is, you have either sovereign immunity or unlimited funds. You don't have to bet the company that the guy doing the inspection really knows what he is doing with that fancy equipment. Further while you can check for voids, disbonds and delamination, it is difficult to detect fiber degradation. While I have great respect for NDT process, it is not. a magic elixir because often the process is flawed, misunderstood or over aggrandized. One need only look at United 232 or Delta 1288 to understand that fact. You can't see the flaw if the process is flawed, no news is just that, no news. When I get back a crankshaft from magna flux with a yellow tag, it only means no cracks detected, it does not mean there are no cracks. There is a reason why Beech decided to buy back all those Starships and poor performance is not the only one, check the box on fiber degradation. Boeing right now is in the process of heavily leveraging the company for a design error.  With the statute of repose at 18 years, there is no reason for Cirrus or any other manufacturer to go beyond a 1000 hour a year equivalence. There is absolutely nothing in it for them.

 

[jaylw314]

On 1/30/2020 at 3:28 AM, misamajoco said:

Do Mooney aircraft have life limits?  For example, the F-18 was designed with a life expectancy of XX hours, however there is are service life extension programs to get them an additional XX hours of service life.  Does the same apply to GA aircraft, specifically Mooney’s?  Yes, I understand Mooney’s are not flown as aggressively as a Hornet and there is not as much stress being induced on the airframe.  However, there are a number of Mooney aircraft that are 50+ years old and I have seen some airframes advertised with as much as 7000+ hours on them which leads me to this question.  Obviously corrosion would have an affect on the life of these aircraft, but is there a requirement to look for cracks or fatigue indicators on an airframe that has more than 5000, 6000 or 7000 hours on it?

Mike Busch did a webinar on metal fatigue (hoping someone else has the link, if I can find it later I'll post it).  Aluminum fatigues from stress cycles, and he suggested the frequency of stresses in airframe components is so low that the life limit of the aluminum is in the tens to hundreds of thousands of hours.  In the motor and firewall forward, with the motor vibrating at 2500 rpm, it might be a different story.

Of course, that doesn't take into account the shape of the components (which might produces stress risers), cracks or corrosion.  

[PT20J]

There used to be a traffic reporter in the SF Bay area in the late 1980's that flew a J that was maintained by Top Gun. Tom Rouch told me that he called the factory when the traffic plane got to 10,000 hours and asked if there was anything special he should look for and Mooney said that only a normal annual inspection was required -- but let them know if he found anything because they'd never seen an airframe with that much time on it. That airplane is still flying and I've seen the current owner post on MS.

I wonder who's Mooney has the highest time? Anyone else with 5 figures?

Skip

[Mooney in Oz]

7 hours ago, PT20J said:

I wonder who's Mooney has the highest time? Anyone else with 5 figures?

About 2005 I saw a J that had ~13,000 airframe hours parked at Gold Coast (Coolangatta) airport. It was from Western Australia.  I believe it is still flying.

[CapPJ]

This is a very interesting topic. I am also looking at purchasing a 201 with just over 10k TTAF hours and was wondering about the limits. This AC was used by the airlines and had good maintenance according to the logs. In contrast another 201 I saw only had 4K TTAF but over the last few years had been flown less than 10 hrs per year average. Last 3 months not even flown. I feel the 10K still a better choice but was wondering if anyone has that many hours on their Mooneys and if so what are your thoughts?

[RoundTwo]

11 minutes ago, CapPJ said:

This is a very interesting topic. I am also looking at purchasing a 201 with just over 10k TTAF hours and was wondering about the limits. This AC was used by the airlines and had good maintenance according to the logs. In contrast another 201 I saw only had 4K TTAF but over the last few years had been flown less than 10 hrs per year average. Last 3 months not even flown. I feel the 10K still a better choice but was wondering if anyone has that many hours on their Mooneys and if so what are your thoughts?

Sounds like the white with green stripe KAL one. 

[gmonnig]

2 minutes ago, CapPJ said:

This is a very interesting topic. I am also looking at purchasing a 201 with just over 10k TTAF hours and was wondering about the limits. This AC was used by the airlines and had good maintenance according to the logs. In contrast another 201 I saw only had 4K TTAF but over the last few years had been flown less than 10 hrs per year average. Last 3 months not even flown. I feel the 10K still a better choice but was wondering if anyone has that many hours on their Mooneys and if so what are your thoughts?

I wouldn't be turned away from a higher time airframe! My last plane had 9600hrs on it and was commenting on by several A&Ps that it was one of the cleanest 1960 Comanches they've ever seen. When I sold it, I had all the inspection panels off the plane for a prebuy. After looking in the engine, he looked inside the plane and couldn't believe what he was looking at. Wrote a check and shook hands. Whole thing took 20mins. My logic is the plane was 62yrs old but averaged 154hrs a year since new! No years of down time to rot, every bolt had been gone through a dozen times over. It's all about how people loved the plane before! My bosses Cessna has 36,000hrs on it. It was a pipeline plane and only had one owner. He's had it for about 10yrs but it's a beautiful 172.

[ArtVandelay]

17 minutes ago, CapPJ said:

This is a very interesting topic. I am also looking at purchasing a 201 with just over 10k TTAF hours and was wondering about the limits. This AC was used by the airlines and had good maintenance according to the logs. In contrast another 201 I saw only had 4K TTAF but over the last few years had been flown less than 10 hrs per year average. Last 3 months not even flown. I feel the 10K still a better choice but was wondering if anyone has that many hours on their Mooneys and if so what are your thoughts?

I’d be more worried about it being used for training, carefully checking landing gear, main spar, and all control rods.

[Hank]

43 minutes ago, CapPJ said:

This is a very interesting topic. I am also looking at purchasing a 201 with just over 10k TTAF hours and was wondering about the limits. This AC was used by the airlines and had good maintenance according to the logs. In contrast another 201 I saw only had 4K TTAF but over the last few years had been flown less than 10 hrs per year average. Last 3 months not even flown. I feel the 10K still a better choice but was wondering if anyone has that many hours on their Mooneys and if so what are your thoughts?

Someone here has / had a J that was used for radio traffic reporting and had 10K hours on it. He reported that the plane flew well, had no unusual problems and completed annual every year without anything major.

Good luck, and let us know how it goes!

[CapPJ]

1 hour ago, ArtVandelay said:

I’d be more worried about it being used for training, carefully checking landing gear, main spar, and all control rods.

Good point and thanks for the advice. Will make sure this gets special attention in PPI.

[CapPJ]

4 hours ago, RoundTwo said:

Sounds like the white with green stripe KAL one. 

That's the one! 

[Justin Schmidt]

On 2/1/2020 at 5:10 PM, CharlesHuddleston said:

Better yet, have you seen some of MY landings!!! 

[Aerodon]

On 1/30/2020 at 8:21 AM, kortopates said:

The only GA airframe that I am aware of with a life limit is the Cirrus SR20 & SR22 airframes with a 12,000 hr life limit. Probably more to do with it being certified under Part 23 than anything else. 

Piper Tomahawk and Piper Seminole have wing life limits.  Around 11,000 hours IIRC.

LET Blanik L13 sailplanes have wing limits too, around 5000 hours IIRC.

Piper Aerostar have windshield limits - 5400 hours IIRC.

Aerodon

 

 

[MikeOH]

I would not be concerned with 10K+ hours from a fatigue point of view, but would want to focus on what has been replaced over the years: heim joints, hinges, jackscrew...i.e. those items that move and wear.

[Will.iam]

Boeing hated the DC-8 so much because they had no life limit so companies like UPS and ATI would not let them go and why would they? They were paid off and making them money. Boeing 757 didn’t offer them anything but fuel savings and less engine maintenance but that didn’t offset a new note. Finally boeing offered a huge discount if they would “trade in” their dc-8 which boeing promptly destroyed so that other companies could not buy them for used parts, forcing other companies to trade in sooner than later. Boeing could make a limitless airframe but that’s bad for continual money income. Just like how software now has switched to a monthly subscription instead of purchasing a version. Hence the moniker”they don’t make them like they used to” because designing something that has limits or doesn’t last past the warranty increases profit. Just saw a water bottle the other day with an expiration date on it! How does water expire? It doesn’t but put an expiration date on it and people with throw away the bottle and buy another and that’s good money for the water bottling company. 

Edited May 2, 2023 by Will.iam

[Schllc]

On 2/2/2020 at 10:39 AM, GeeBee said:

 Further while you can check for voids, disbonds and delamination, it is difficult to detect fiber degradation. 

 

While in college I built, rode, and raced bicycles.
This was during the infancy of mountain biking and huge leaps were being made in frame and component design.
The demands for lighter materials, was at the same time bicycles were being subjected to much more hostile stresses, and aluminum and carbon fiber rushed to the front of the pack. 
All of a sudden frames started failing. At first in was aluminum, in the high stress areas like the crank housing or headset(where the forks go to the handlebars), or the rear axle frame mounts, this material fell out of favor and carbon rose. But then random failures started occurring and without warning. We are talking total catastrophic failure.
Unlike with aluminum which would have a slow decline to the point you knew a failure was imminent, but even then a large degree of function remained so you could get home, carbon fiber just failed completely rendering the bike unusable. 
if you look today you will see most are made of aluminum or steel. 
I would not suggest carbon fiber is inferior or unable to be used reliably, but I will submit that the homogeneous nature of their construction will always be a challenge to properly inspect, and the failures will be much the same, albeit hopefully much less frequent. 
There is very little strength left after the modulus of elasticity of carbon fiber has been exceeded,  but more importantly that value after failure is unpredictable and wildly varying, while metal is much more predictable.  
To be fair,  bicycle companies don’t have to document and test things the way aircraft manufacturers do, but the base nature of the material is the same….

 

[A64Pilot]

So fas as I know no CAR 3 airplane has life limits. Except when those are imposed by AD, one I’m most familiar with most is main spar life limits on Thrush Crop Dusters. FAR 23 requires life limits.   I can’t quote Chapt and Verse but the Thrush S2R-T660 is the only fully FAR 23 crop duster and it has several life limited components, all in the wing. I wasn’t there when that aircraft was Certified.

CAR 3 has some verbiage along the lines of fatigue must be considered where FAR 23 requires it to be calculated or similar language. You get very different “scatter factors” from analysis and testing. For instance Analysis gave the new wing spar life limit of 29,000 hours, but with the H-80 we instrumented the aircraft and I went out and flew test points and testing moved the life limit to 60,000 hours, we could have gotten more but doubling it sounded good and why bother? FAA drug us into being FAR 23 compliant with wing spars as the old design had failed, killing people and was the subject of several AD’s, the new spar was a terminating action.

I said fully FAR 23 compliant because it’s normal if you Certify something new under CAR 3 because it’s an existing design for the FAA to force you into FAR 23 in some instances so you meet some FAR 23 standards but still have a CAR 3 airplane.

Mooney has I believe some recommended replacement intervals like the unavailable no back spring, but it’s not life limited. Life limited means you must whether you fly part 91 or not.

FAA is of the opinion that everything fatigues and will eventually fail, but that’s not true. If for example I gave you a rail road spike and told you to bend it back and forth by hand it will never break, because you can’t impart enough force by hand to fatigue it. If an FAA person ever tells you that everything fatigues, ask them what the 172’s wing spar life limit. Apparently if flown within certified limits it’s outside of the fatigue cycle. So it’s possible to build something that doesn’t fatigue.

But it’s incorrect to state that aluminum won’t fatigue for 10’s of thousands of hours, older Air Tractor aluminum wing spars fatigue and break way before then. Nothing magic about aluminum, Titanium? Yeah there may be some magic there, but good ole 4130 or better 4340 steel can be made to where it will outlast the airplane, just takes a re-design.

https://www.federalregister.gov/documents/2008/04/28/E8-9058/airworthiness-directives-air-tractor-inc-models-at-300-at-301-at-302-at-400-and-at-400a-airplanes

[Greg Ellis]

On 5/1/2023 at 4:20 PM, Aerodon said:

Piper Tomahawk and Piper Seminole have wing life limits.  Around 11,000 hours IIRC.

LET Blanik L13 sailplanes have wing limits too, around 5000 hours IIRC.

Piper Aerostar have windshield limits - 5400 hours IIRC.

Aerodon

 

 

I thought the Rockwell Commander 112/114/115 had wing life limits as well so a quick search showed that they do.  Page 11 of the following FAQ page.

Commander Aircraft FAQ

 

[carusoam]

On 5/2/2023 at 6:46 AM, Schllc said:

While in college I build, rode, and raced bicycles. This was the infancy of mountain biking and huge leaps were being made in frame and component design.
The demands for lighter materials, was at the same time bicycles were being subjected to much more hostile stresses, and aluminum and carbon fiber rushed to the front of the pack. 
All of a sudden frames started failing. At first in was aluminum, in the high stress areas like the crank housing or headset(where the forks go to the handlebars), or the rear axle frame mounts, this material fell out of favor and carbon rose. But then random failures started occurring and without warning. We are talking total catastrophic failure.
Unlike with aluminum which would have a slow decline to the point you knew a failure was imminent, but even then a large degree of function remained so you could get home, carbon fiber just failed completely rendering the bike unusable. 
if you look today you will see most are made of aluminum or steel. 
I would not suggest carbon fiber is inferior or unable to be used reliably, but I will submit that the homogeneous nature of their construction will always be a challenge to properly inspect, and the failures will be much the same, albeit hopefully much less frequent. 
There is very little strength left after the modulus of elasticity of carbon has been exceeded,  but more importantly that value after failure is unpredictable and wildly varying, and metal is much more predictable.  
To be fair,  bicycle companies done have to document and test things the way aircraft manufacturers do, but the base nature of the material is the same….

 

Seeing if @aviatoreb is around for this one…

 

best regards,

-a-

-a-

[DXB]

Despite the relatively modest hours (5k) on my 55 year old M20C, one thing that worries me about this geriatric bird is that the spar must be inspected annually for continued airworthiness - seemingly a very reasonable requirement. However, there is a portion of the spar that cannot readily be inspected.  There was someone here who stripped his tanks for reseal only to find a corroded spar under the sealant that totaled the airframe.  That part of my spar is now hidden by bladders, and I'm sure no one looked under the sealant before they were put in. 

[A64Pilot]

28 minutes ago, DXB said:

Despite the relatively modest hours (5k) on my 55 year old M20C, one thing that worries me about this geriatric bird is that the spar must be inspected annually for continued airworthiness - seemingly a very reasonable requirement. However, there is a portion of the spar that cannot readily be inspected.  There was someone here who stripped his tanks for reseal only to find a corroded spar under the sealant that totaled the airframe.  That part of my spar is now hidden by bladders, and I'm sure no one looked under the sealant before they were put in. 

You know I hate to say it, but there are a lot of things like that.

We magnaflux connecting rods and crankshafts during overhaul, but it’s just not realistic to do so any other time and rods and crankshafts do occasionally let go from cracking.

You takes your chances when you buy a ticket, we do what we can to reduce risks, but you can’t drive them to zero.

But in your case I’d take solace in knowing what the main spar failure rate is, and what the cause was. Have any failed without being subjected to extreme overload?

[aviatoreb]

59 minutes ago, carusoam said:

Seeing if @aviatoreb is around for this one…

 

best regards,

-a-

-a-

Much of what you say is true but some is not my experience at all.

I have been around bikes a long time since about 19, and now I am ...oh my gosh... just turned 56...and I used to ride what was then the leading edge stuff - and I broke A LOT of stuff being larger than the standard sized rider.  I used to be once upon a time a national level track racer - velodrome.  I remember when disc wheels were things you only saw in magazines and I somehow managed to get a Russian built carbon fiber disc wheel when I was racer at the Colorado Springs velodrome and some national team member had somehow gotten it also in a barder.  I loved that thing and thought I looked so cool with it, until I traded it for something else.  I think that was a rubberized sleek shiny skin suit with long sleeve arms and ridges on the should to trip the Flow.  Who knows if any of that stuff helped but we sure looked good!

..and I still ride...less fast, but with a much bigger wallet!

So in my lifetime I have broke a total of 4 cranksets - I am here to tell you that when aluminum gives way it just snaps abruptly.  I musta been a beast peddling too hard - hahaaa

I've broken several framests, and seen several framesets break.  I am not counting the ones that break because you crash them.  My favorite stupid frameset trick was once in the Davis 4th of July criterium, 1988? and I was third wheel coming out of the last corner which is absolutely perfect positioning to make a run at the line, and like 100 guys behind me. I stood up to crank out my spring and the chain stay separated from the down tube and then that caused the rear wheel to bend sideways, and from there I was going sides ways and both my tires rolled off (glue on tubulars) and well then ... crashed.  And a bunch of guys crashed on top of me.  In fact it turns out, didn't know until a year later, that one guy broke his shoulder and held a grudge against me and I ran into him in a race in Napa Valley the next year, wherein he pulled along side me and started punching me!  Good thing I was lots bigger than him.

I have broken soooo much stuff over the years - of all materials, steel, aluminum, titanium, and carbon fiber.  frames, wheels, pedals, cranksets, forks, seats, seat posts, and on and on.  :-O. Sometimes leading to crashes.  Sometimes just to nuisances - like having to peddle home 10 miles with only one crank.  Or no seat standing up.  Anyway since a long time, weight is the last thing I am looking for when I purchase a bike or a part - I am looking for a robust build.  And a lot of my stuff is custom built extra beefy - "Clydesdale" build.

Carbon is no better or worse than the other stuff.  None.  Its how well its engineered.  And good engineers a this point understand very well how each of these materials is stressed, ages, and so forth and how much margin to build in when selecting materials and selecting how much to build and over build into their designs based on expected stresses.  My 25 year old son is exactly the same size and build I was when I was his age.  I think he is 210 right now and he measures watts which I was not able to do back in the day since the technology didn't exist yet - he sprints at 1750 watts.  He has been riding the same carbon fiber Cervelo since he got it when he was 18 and its holding up great.  He is an aeronautical engineering PhD student and well aware of how to inspect his bike for signs of onset of failures so I am confident in him.  He did once break a pedal - by Saris power pedal - and that caused a crash and a broken wrist.  I kinda wish he hadn't followed this hobby of mine.  :-O

Edited May 3, 2023 by aviatoreb