I was just discussing the SAIB with partner IA here at work. The fact that the FAA actually put out some information is impressive in itself. Back in Jan/Feb I was calling some contacts and emailing trying to get this exact information. Obviously SMS takes a back seat at the FAA for information posting. . With todays tech this information should be made available in real time. I was really pissed at some stonewalling, but hey, only most of a year to get it out.
Cmill7: my take is this. If you are under the factored hours, your discretion. Caveat is there is a "possibility" of doing damage to the holes any time you take them out. On some planes will be a crap shoot but just keep in mind. On my picture above , that warrior had 17000 hours. But as noted, many are showing up with issues well before that. Would i do it on mine if not required? Most likely especially now we see that these are NOT isolated events.
NOW here is the kicker.
When the NPRM came out I commented that the scope was way too narrow. My research of damage and totaled aircraft from many sites showed breaks of spars ,,, RIGHT AT SUSPECT HOLES on aircraft where wings broke off due to hard landings or just runway incursions. The last one i found was a pa32, rgt wing broke after runway excursion! My suggestion,,, this goes for EVERYONE.... If in your logs, you have ANY event that required wing removals, any event such as wing hit that required leading edge skin replaced, or even any hard landing that flattened a strut, ( or broke a gear off heaven forbid) you are most certainly a candidate for bolt hole inspection. I would also suggest at the next annual inspection, ask maintenance to remove sidewall panel enough to check security of the wing FWD mount bolt. IF this is loose,, next do the wing bolts eddy current. Aft spar bolts easy to see.
The FAA ignored my comments and phots i sent. And now we are at this point. I wish this were just isolated numbers, but Jims numbers, just from his group, are alarming.
So maybe a a plane that has 17,000 hrs, and never experienced a hard landing is fine, but one with 4800 and is poorly landed repeatedly, is going to develop cracking. I’ve only flown one other Cherokee other than our Archer, and it was a short orientation flight, so my experience is limited. Do the Hershey wing aircraft tend to land smoother than the tapered wings? My understanding is the tapered wing was introduced to improve stall characteristics, does that mean it is more likely to thunk onto the runway and float less? Just pondering what all this means.
HI Spike, seeing that we are seeing a wide range of hours, yes it could be possible for a lower time aircraft to develope cracking IF it has been subject to certain types of unusual damages. Overall the design is safe, its been around a long time but I am thinking that damage tolerance , something we know more about now, may not be as wide as everyone thought. My circle of IA buddies feel the same way that if you have had, or experience a event out of the ordinary, may be prudent to do spar inspections.
Will leave the flight characteristics between wings for other experts to chime in on. LOL
The 17000 hour spar above, due to damage in the holes, would have been unable to perform a bolt hole eddy current. Not to mention, holes so worn as to make bolts a loose fit. I told the FBO to get it out of fleet. They did. I didn't want anybody else's name on it.
I have many hours in both the tapered wing and Hershey bar PA28's.
It's often said that when the Hershey bar wing is done flying, it's done, and if you're not down, you'll arrive with a thump. The tapered wing has a higher aspect ratio, floats better and therefore tends to land easier.
My opinion: when a pilot employs proper technique, the Hershey bar PA28's can be landed just as gently. On the other side, treat it wrong, and you can thump a tapered wing onto the runway too.
It's up to the pilot to adapt his/her technique to what the airplane needs.
I contacted the FAA to mention 2 things regarding the SAIB,
RE The PA44: not only do the wings have a life limit, the wing spar carry through and attaching structure also is included in the same limitations, this totals the aircraft.
RE number of failures chart: In figure 3 the number of inspected aircraft of each model would be helpful information, as well as average factored service hours of models tested vs models with discrepancies.
I did not mention, but I really would like to know what the final outcome was on the "suspect" aircraft mentioned in the SAIB with less than 4000 hours.
The FAA factored service life calculation does not use age at all. I have run the numbers on my plane for 6000 hours wing total time in service. The FAA method results in 2235.3 FSH whereas the EASA method results in 866.67 FSH. If my PA-28 was 20 years old, the EASA FSH would be 4133.
I believe hard landings could be a factor in these wing spar failures based upon the prominence of lower forward bolt hole cracks. A loose fastener at the forward attach point was also suggested in the past by a few people.
The factored factor , while it seemed strange in the beginning, made sense after running the numbers on a couple of fleet planes versus normal use planes. In GA, we do not keep track of landings and takeoffs like we do here in the airlines. Some amazingly clever FAA person came up with the formula to emulate what TO and Landing cycles calcs might look like for 'training " aircraft if we actually did keep track that way. Hence the kicker is number of 100hr inspections ( req for training) to be a key factor in the calc. Now of course i have never had a hard landing,, but we all know airplanes that have! So if every plane had a g meter and a requirement to insp after a hard landing,,, things might be or could be different. The only way i know you had a hard landing if if you tell me or i see the wrinkles.
At airline, pilot write em up and we can verify with FDR data to be sure, which also guides which inspections are needed.
I have just join the "Piper Owners" and seriously considering buying a '71 PA-28R 200 with 3700 hours owned by the current owner for the past 40 years here is Australia. Despite the AD I have no immediate concerns about the integrity of the PA28 family of aircraft.
Before going ahead I wanted to get some perspective on the wing spar AD, which is worth bearing in mind, but wonder if what the FAA are trying to do is cater for somewhat abused aircraft that have slipped through the cracks - no pun intended.
While it can be determine what type of life an aircraft has had, with some accuracy, we are unable to determine how the aircraft was treated and how well it was maintained. Furthermore, not all hours are equal with respect to fatigue. For example, you could have two aircraft with similar hours one used for training, lots of touch and goes, and one, say, solely used for transport. What we don't know is the cycles, how well the aircraft was maintained eg were the tyres inflated correctly, if the oleos were at the right pressure, what the average operating weight of the aircraft was, the number of hard or heavy landings etc etc. Unlike the airlines and charter operators GA flying is largely an honour system with no objective means of monitoring what is actually happening to the aircraft on a daily basis.
I used the term "abused" earlier which I would characterise as anytime a hard landing is not recorded, anytime line maintenance, ie daily inspections are just signed off, anytime maintenance is not carried out correctly, or if the aircraft was operated outside of the envelop, just to name a few.
In recent times I witnessed, inter alia, a couple of things which I think bears testament to what I'm driving at. While participating in gliding ops I saw a glider hit a gable marker, land hard and then ground loop into a fence. To my horror this glider was back in the air 30 minutes later. The second thing was just the other day, with an aircraft I was interested in, where the owner refused to undertake a recommended bulk strip of an engine after metal was found in the filter. He elected to take the aircraft off the market and start flying it again without further reference. These two examples are not an oranges compared to oranges analysis with the AD but an illustration of the mentality of some people and, I would hope, is what the majority of owner/operators have to contend with.
Back to the AD, and thinking out aloud here, given the thousands of aircraft affected surely we can come up with something better than second hand wings or 300 day lead times for replacement spars. I would have thought that some enterprising aircraft fabricators could produce these to the original spec and improve on the design ie, to be more damage tolerant. I'm assuming that a lot of the damage in the hole is caused by steel bolts fitted into an aluminium spar as indicated by the scratching and scoring that is occurring. Someone with more engineering knowledge than me could answer this but is it feasible to ream the hole and fit bushing to alleviate the direct damage to the spar. I suspect this might become a chicken and egg story, but is the scratching and scoring in the hole always present with cracking. Maybe bushings containing some form of indicating dye might work here.
As a final point one can't help to express some disappointment with the FAA in all this who seem to be somewhat reactive to these problems. It shouldn't be enough that the solution is inspection and replacement. More needs to be done. While all the talk amongst pilots is about looking after the engine and all things that propel us, in my opinion there is less talk and emphasis about the thing that carries all the load. If the engine fails then the airframe still flies and carries us safely back to earth. However, if the airframe fails no amount of thrust and cursing is going to save the day. Non-moving parts does not mean no wear and tear. Where public safety is concerned we know to the second what an airliner is doing and any given point in time and space. But what do we know about GA aircraft apart from TTIS, Engine hours SMOH and Prop hours SMOH. Well ...nothing much more than a subjective point of view on how the aircraft was operated. "Caveat Emptor" starts to ring true. Maybe it's time we consider, more intensively, aircraft cycles and exceedances such as landing "g", overspeeds and overloading. The aggregate of all these plus time contribute to airframe micro failures. This might be a holistic way to come up with factored hours instead of the gross all encompassing way the FAA has proposed this ...but I guess that's all the FAA has to go on as well which is a failure in and of itself.
In conclusion maybe there needs to be a rethink on how GA aircraft are monitored and surveyed because the current system has a lot of (Swiss cheese) holes if you get my drift. Maybe there is an argument to not only record hours as the only important metric that determines fatigue but to record and report all aircraft cycles - one touch and go or one landing equals one cycle. Furthermore, non resettable "g" meters should be fitted to all aircraft but, at a minimum, to all aircraft engaged in ab-initio training with that meter staying with the aircraft for the rest of its life. A smart person with a slide rule should then be able to come up with a better formula that produces a more considered aggregated factored hours to calculate component life. More difficult engineering problems have been solved in the past. While I understand money is tight I am sure the industry has the ability to produce the required components at the economies of scale that makes it a viable proposition and non event for the average owner.
These things usually play out because of some form of unreported abuse of the aircraft. Unfortunately it turns up hours if not years later and some unsuspecting pilot usually suffers the consequences. When an incident occurs a psychology plays out where the stakes are either personal embarrassment, deliberate violation discovery or a financial burden that prevents the true nature of how an aircraft has been treated throughout its life. Furthermore, and, moreover, it is anathema to me that any regulatory authority would be asking for answers from the very imperfect system it oversees, that caused the problem in the first place, for advice. When an incident occurs or an an aircraft is abused it is a human instinct to either keep quiet or as we say in the Australian vernacular, "she'll be right". Unfortunately that attitude to minimise an event does not work in aviation.
Realizing this is an older thread, BarneyW raises some good thoughts I am sure shared by many of our readers. However, here in the US, if the FAA issues an AD, that is a MANDATORY call to action for the owner/operator. The AD must be followed to the letter, or if there is an alternative method of compliance suggested AND APPROVED, that will do as well. All we can really do is comment when, thankfully asked, during the proposed Notice of Proposed Rule Making. I applaud the FAA for soliciting those comments!
On a related note, I often wondered why there are 12 bolts holding on the wing spar if, when only one fails, the entire structure is in danger of coming apart?! Was 12 not enough to provide a generous margin of safety, normal loads considered?
Another point to ponder; in the helicopter world, there is a load limit on the main rotor bearings. If that limit is exceeded, as determined by letting the rotor RPM go too high, the manufacturer has very specific rotor hub inspection requirements. Airplanes have load limits too, but I know of no inspection required if the pilot exceeds structural airspeed limits. To BarneyW's point, In both cases, heli or fixed wing, it is still an honor system that the "transgression" be reported and possible damage be investigated. For example, how many have inadvertently extended flaps above the white arc? After 50 years of flying; guilty as charged, and a voluntary inspection by an A&P/IA followed. But who knows how many time the previous owner did this? As Harry Potter said, "Its.... Complicated."
Regards,
Mike
Michael Jay Jones (MikeJJ)
Piper Owners Aviation Director, Forum Moderator, Author
Thanks Mike I appreciate the input and the points you made. I guess part of my post was philosophical and the other based in reality. Yes I get it that the ADs are mandatory but interestingly the aircraft I am looking at is not required to do it as it falls well short of the hours, factored or otherwise. I'm half tempted to get it done anyway but I got the sense that the cure is worse than the disease that being the potential damage to the area in trying to knock out bolts that have (in jest) bonded at the molecular level after 53 years.
Anyhow we'll see how it goes with the pre-purchase inspection.
In typical government and FAA procedure. In other words, they are not using their own SMS requirements to disseminate information, We really don't have any current datahow many defective spars we have seen across the fleets. That being said, Barney, take a look at my previous comments in his thread to get an idea where I stood and where I stand on the current State of this issue.
I told the FAA in the NP. R. M that they did not go far enough based on my research of scouring decades of accident, aircraft and pictures from salvage sites. I gave them the data and the photos and they ignored it.
You are both correct in the fact that we Use the honor system for recording events to general aviation aircraft , really, there's no way around that and there are many cases I have seen of poor recording and or actual cover up of potential damage. The only recourse, a buyer or owner has is to have a very knowledgeable mechanic. Research the log books and correlate to what he sees on the aircraft . if there is any doubt, just do the A. D and get the piece of mind as well as documentation that there are no detectible defects. My current view of the FAA is that they are very ineffective if only reactive at this point based on personal experience as well as current events in the industries. And I don't see this trend going in the right direction
Mike I'm not sure what the criteria is for being an "older thread" but correct me if I'm wrong the AD is required for aircraft having reached either 5000hrs TTIS or 5000hrs factored. It is therefore feasible that there are a number of aircraft every year that will be captured by this AD so it's going to be a topic for discussion for quite some time. Would you agree?
Carl from my aviation experience I learnt quite some time ago that the FAA started outsourcing their services to delegates for engineering and most likely other surveillance activities.
I guess the burning question I have for owners who own or about to buy, relatively speaking, a low time Cherokee, would they still carry out the AD and why?
You're correct and stating that this will be an ongoing issue with all the affected cherokees For every year. There will be new groups of aircraft that fall under the AD either total hours or factored hours. The problem I'm trying to deal with right now is the fact that the people the write airworthy Distractives are probably the least qualified people because they never worked on the airplanes . I'm dealing with that a much larger environment.
As I mentioned, you have to correlate log books with what you see on the airplane, especially if it technically is not do yet, we've had several ownetson our field do the ad prematurely with no issues. Yes, you can cause issues by improper bolt removal. The biggest problem with the NDT which is something I do at work, is if you have corrosion or scoring in the bore that makes it hard to distinguish a defect from the background noise. On some aircraft, it could be a Crap shoot. There's no easy answer and each aircraft. I would say is it's own. Particular case to analyze
Continuing the intermittent discussion on this topic, which has understandably gone dormant pending further direction from the FAA.
Mike, in relation to your question about fastener redundancy, my purely speculative response is that the problem in question has very little relation to the number or sequence of bolts. The photos suggest that the failure mode totally circumvents any redundancy offered by the additional rows of bolts, unfortunately. The crack propagates across the width of the spar, inboard of the other bolts. Therefore, when the crack completes, the wing separates with all the outboard spar fasteners still securely attached to the now-separated portion. Please, someone feel free to correct me if I am way off base with my understanding of this.
Barneyw, a conundrum indeed. The non-zero risk of a spar crack has to be weighed against the non-zero risk of a false positive and the non-zero risk of inducing secondary damage and bolt hole wear from the inspection itself.
Importantly, with regard to the eddy current inspection, do we have a firm (or even loose) handle on the number needed to "treat" vs the number needed to "harm?" I'm no aerospace engineer, but in medicine, we have learned the hard way many times over that shotgun, blanket, and "common-sense" approaches to testing tend to do more harm than good when analyzing outcomes on a population level.
(As an aside: A couple of you in this thread helped me out with my NLG incident a couple months ago, at which time I had considered stepping away after it was totaled by insurance... well, a month later, I decided I had stepped away long enough lol. Under contract for a Turbo Arrow III with TTAF 3200 and FSH < 200, which is what led me to this thread.)
Regarding "doing the AD early" with regard to the eddy current inspection.
Recently a friend did the AD on a PA28-161 200 hours early, and was given an AMOC from the FAA. The general rule seems to suggest that you should be in the window where 90% of the specified "life" should have passed. Otherwise, you will need to do the eddy current inspection again after the defined service life interval.
I'd be very interested to see why and what the AMOC was for. You are under no obligation to perform a AD before any specified time , thats owner discretion... Carl
I believe I posted this comment previously (more than 3 years ago) but pulling those bolts from the wing spar DOES impact the integrity of the wing. Previous ADs and, as I've read, a few of the subsequent accidents were attributed to the removal of those bolts which compromised an, otherwise, sound wing spar.
Is this Piper suggesting a lifetime limit or am I misreading? thinking of buying a PA-32 with 8000TTIS (wing spar AD’EC test performed and passed) and curious to know if it’s got 4000 hours before getting turned into a Coke can. (not that I’m likely to live long enough to see it)
Comments
Scott, thanks for the comments.
I was just discussing the SAIB with partner IA here at work. The fact that the FAA actually put out some information is impressive in itself. Back in Jan/Feb I was calling some contacts and emailing trying to get this exact information. Obviously SMS takes a back seat at the FAA for information posting. . With todays tech this information should be made available in real time. I was really pissed at some stonewalling, but hey, only most of a year to get it out.
Cmill7: my take is this. If you are under the factored hours, your discretion. Caveat is there is a "possibility" of doing damage to the holes any time you take them out. On some planes will be a crap shoot but just keep in mind. On my picture above , that warrior had 17000 hours. But as noted, many are showing up with issues well before that. Would i do it on mine if not required? Most likely especially now we see that these are NOT isolated events.
NOW here is the kicker.
When the NPRM came out I commented that the scope was way too narrow. My research of damage and totaled aircraft from many sites showed breaks of spars ,,, RIGHT AT SUSPECT HOLES on aircraft where wings broke off due to hard landings or just runway incursions. The last one i found was a pa32, rgt wing broke after runway excursion! My suggestion,,, this goes for EVERYONE.... If in your logs, you have ANY event that required wing removals, any event such as wing hit that required leading edge skin replaced, or even any hard landing that flattened a strut, ( or broke a gear off heaven forbid) you are most certainly a candidate for bolt hole inspection. I would also suggest at the next annual inspection, ask maintenance to remove sidewall panel enough to check security of the wing FWD mount bolt. IF this is loose,, next do the wing bolts eddy current. Aft spar bolts easy to see.
The FAA ignored my comments and phots i sent. And now we are at this point. I wish this were just isolated numbers, but Jims numbers, just from his group, are alarming.
48 yrs A/P IA DAL aircraft inspector. 172N
So maybe a a plane that has 17,000 hrs, and never experienced a hard landing is fine, but one with 4800 and is poorly landed repeatedly, is going to develop cracking. I’ve only flown one other Cherokee other than our Archer, and it was a short orientation flight, so my experience is limited. Do the Hershey wing aircraft tend to land smoother than the tapered wings? My understanding is the tapered wing was introduced to improve stall characteristics, does that mean it is more likely to thunk onto the runway and float less? Just pondering what all this means.
HI Spike, seeing that we are seeing a wide range of hours, yes it could be possible for a lower time aircraft to develope cracking IF it has been subject to certain types of unusual damages. Overall the design is safe, its been around a long time but I am thinking that damage tolerance , something we know more about now, may not be as wide as everyone thought. My circle of IA buddies feel the same way that if you have had, or experience a event out of the ordinary, may be prudent to do spar inspections.
Will leave the flight characteristics between wings for other experts to chime in on. LOL
The 17000 hour spar above, due to damage in the holes, would have been unable to perform a bolt hole eddy current. Not to mention, holes so worn as to make bolts a loose fit. I told the FBO to get it out of fleet. They did. I didn't want anybody else's name on it.
48 yrs A/P IA DAL aircraft inspector. 172N
Spikecarter;
I have many hours in both the tapered wing and Hershey bar PA28's.
It's often said that when the Hershey bar wing is done flying, it's done, and if you're not down, you'll arrive with a thump. The tapered wing has a higher aspect ratio, floats better and therefore tends to land easier.
My opinion: when a pilot employs proper technique, the Hershey bar PA28's can be landed just as gently. On the other side, treat it wrong, and you can thump a tapered wing onto the runway too.
It's up to the pilot to adapt his/her technique to what the airplane needs.
Jim "Doc Griff" Griffin
PA28 - 161
Chicago area
I contacted the FAA to mention 2 things regarding the SAIB,
RE The PA44: not only do the wings have a life limit, the wing spar carry through and attaching structure also is included in the same limitations, this totals the aircraft.
RE number of failures chart: In figure 3 the number of inspected aircraft of each model would be helpful information, as well as average factored service hours of models tested vs models with discrepancies.
I did not mention, but I really would like to know what the final outcome was on the "suspect" aircraft mentioned in the SAIB with less than 4000 hours.
The FAA factored service life calculation does not use age at all. I have run the numbers on my plane for 6000 hours wing total time in service. The FAA method results in 2235.3 FSH whereas the EASA method results in 866.67 FSH. If my PA-28 was 20 years old, the EASA FSH would be 4133.
I believe hard landings could be a factor in these wing spar failures based upon the prominence of lower forward bolt hole cracks. A loose fastener at the forward attach point was also suggested in the past by a few people.
John Schreiber
A&P, IA, CMEL
978mhz.com
The factored factor , while it seemed strange in the beginning, made sense after running the numbers on a couple of fleet planes versus normal use planes. In GA, we do not keep track of landings and takeoffs like we do here in the airlines. Some amazingly clever FAA person came up with the formula to emulate what TO and Landing cycles calcs might look like for 'training " aircraft if we actually did keep track that way. Hence the kicker is number of 100hr inspections ( req for training) to be a key factor in the calc. Now of course i have never had a hard landing,, but we all know airplanes that have! So if every plane had a g meter and a requirement to insp after a hard landing,,, things might be or could be different. The only way i know you had a hard landing if if you tell me or i see the wrinkles.
At airline, pilot write em up and we can verify with FDR data to be sure, which also guides which inspections are needed.
48 yrs A/P IA DAL aircraft inspector. 172N
Hi All
I have just join the "Piper Owners" and seriously considering buying a '71 PA-28R 200 with 3700 hours owned by the current owner for the past 40 years here is Australia. Despite the AD I have no immediate concerns about the integrity of the PA28 family of aircraft.
Before going ahead I wanted to get some perspective on the wing spar AD, which is worth bearing in mind, but wonder if what the FAA are trying to do is cater for somewhat abused aircraft that have slipped through the cracks - no pun intended.
While it can be determine what type of life an aircraft has had, with some accuracy, we are unable to determine how the aircraft was treated and how well it was maintained. Furthermore, not all hours are equal with respect to fatigue. For example, you could have two aircraft with similar hours one used for training, lots of touch and goes, and one, say, solely used for transport. What we don't know is the cycles, how well the aircraft was maintained eg were the tyres inflated correctly, if the oleos were at the right pressure, what the average operating weight of the aircraft was, the number of hard or heavy landings etc etc. Unlike the airlines and charter operators GA flying is largely an honour system with no objective means of monitoring what is actually happening to the aircraft on a daily basis.
I used the term "abused" earlier which I would characterise as anytime a hard landing is not recorded, anytime line maintenance, ie daily inspections are just signed off, anytime maintenance is not carried out correctly, or if the aircraft was operated outside of the envelop, just to name a few.
In recent times I witnessed, inter alia, a couple of things which I think bears testament to what I'm driving at. While participating in gliding ops I saw a glider hit a gable marker, land hard and then ground loop into a fence. To my horror this glider was back in the air 30 minutes later. The second thing was just the other day, with an aircraft I was interested in, where the owner refused to undertake a recommended bulk strip of an engine after metal was found in the filter. He elected to take the aircraft off the market and start flying it again without further reference. These two examples are not an oranges compared to oranges analysis with the AD but an illustration of the mentality of some people and, I would hope, is what the majority of owner/operators have to contend with.
Back to the AD, and thinking out aloud here, given the thousands of aircraft affected surely we can come up with something better than second hand wings or 300 day lead times for replacement spars. I would have thought that some enterprising aircraft fabricators could produce these to the original spec and improve on the design ie, to be more damage tolerant. I'm assuming that a lot of the damage in the hole is caused by steel bolts fitted into an aluminium spar as indicated by the scratching and scoring that is occurring. Someone with more engineering knowledge than me could answer this but is it feasible to ream the hole and fit bushing to alleviate the direct damage to the spar. I suspect this might become a chicken and egg story, but is the scratching and scoring in the hole always present with cracking. Maybe bushings containing some form of indicating dye might work here.
As a final point one can't help to express some disappointment with the FAA in all this who seem to be somewhat reactive to these problems. It shouldn't be enough that the solution is inspection and replacement. More needs to be done. While all the talk amongst pilots is about looking after the engine and all things that propel us, in my opinion there is less talk and emphasis about the thing that carries all the load. If the engine fails then the airframe still flies and carries us safely back to earth. However, if the airframe fails no amount of thrust and cursing is going to save the day. Non-moving parts does not mean no wear and tear. Where public safety is concerned we know to the second what an airliner is doing and any given point in time and space. But what do we know about GA aircraft apart from TTIS, Engine hours SMOH and Prop hours SMOH. Well ...nothing much more than a subjective point of view on how the aircraft was operated. "Caveat Emptor" starts to ring true. Maybe it's time we consider, more intensively, aircraft cycles and exceedances such as landing "g", overspeeds and overloading. The aggregate of all these plus time contribute to airframe micro failures. This might be a holistic way to come up with factored hours instead of the gross all encompassing way the FAA has proposed this ...but I guess that's all the FAA has to go on as well which is a failure in and of itself.
In conclusion maybe there needs to be a rethink on how GA aircraft are monitored and surveyed because the current system has a lot of (Swiss cheese) holes if you get my drift. Maybe there is an argument to not only record hours as the only important metric that determines fatigue but to record and report all aircraft cycles - one touch and go or one landing equals one cycle. Furthermore, non resettable "g" meters should be fitted to all aircraft but, at a minimum, to all aircraft engaged in ab-initio training with that meter staying with the aircraft for the rest of its life. A smart person with a slide rule should then be able to come up with a better formula that produces a more considered aggregated factored hours to calculate component life. More difficult engineering problems have been solved in the past. While I understand money is tight I am sure the industry has the ability to produce the required components at the economies of scale that makes it a viable proposition and non event for the average owner.
These things usually play out because of some form of unreported abuse of the aircraft. Unfortunately it turns up hours if not years later and some unsuspecting pilot usually suffers the consequences. When an incident occurs a psychology plays out where the stakes are either personal embarrassment, deliberate violation discovery or a financial burden that prevents the true nature of how an aircraft has been treated throughout its life. Furthermore, and, moreover, it is anathema to me that any regulatory authority would be asking for answers from the very imperfect system it oversees, that caused the problem in the first place, for advice. When an incident occurs or an an aircraft is abused it is a human instinct to either keep quiet or as we say in the Australian vernacular, "she'll be right". Unfortunately that attitude to minimise an event does not work in aviation.
Looking forward to any comments.
Cheers
Realizing this is an older thread, BarneyW raises some good thoughts I am sure shared by many of our readers. However, here in the US, if the FAA issues an AD, that is a MANDATORY call to action for the owner/operator. The AD must be followed to the letter, or if there is an alternative method of compliance suggested AND APPROVED, that will do as well. All we can really do is comment when, thankfully asked, during the proposed Notice of Proposed Rule Making. I applaud the FAA for soliciting those comments!
On a related note, I often wondered why there are 12 bolts holding on the wing spar if, when only one fails, the entire structure is in danger of coming apart?! Was 12 not enough to provide a generous margin of safety, normal loads considered?
Another point to ponder; in the helicopter world, there is a load limit on the main rotor bearings. If that limit is exceeded, as determined by letting the rotor RPM go too high, the manufacturer has very specific rotor hub inspection requirements. Airplanes have load limits too, but I know of no inspection required if the pilot exceeds structural airspeed limits. To BarneyW's point, In both cases, heli or fixed wing, it is still an honor system that the "transgression" be reported and possible damage be investigated. For example, how many have inadvertently extended flaps above the white arc? After 50 years of flying; guilty as charged, and a voluntary inspection by an A&P/IA followed. But who knows how many time the previous owner did this? As Harry Potter said, "Its.... Complicated."
Regards,
Mike
Thanks Mike I appreciate the input and the points you made. I guess part of my post was philosophical and the other based in reality. Yes I get it that the ADs are mandatory but interestingly the aircraft I am looking at is not required to do it as it falls well short of the hours, factored or otherwise. I'm half tempted to get it done anyway but I got the sense that the cure is worse than the disease that being the potential damage to the area in trying to knock out bolts that have (in jest) bonded at the molecular level after 53 years.
Anyhow we'll see how it goes with the pre-purchase inspection.
Cheers
Barney and Mike.
In typical government and FAA procedure. In other words, they are not using their own SMS requirements to disseminate information, We really don't have any current datahow many defective spars we have seen across the fleets. That being said, Barney, take a look at my previous comments in his thread to get an idea where I stood and where I stand on the current State of this issue.
I told the FAA in the NP. R. M that they did not go far enough based on my research of scouring decades of accident, aircraft and pictures from salvage sites. I gave them the data and the photos and they ignored it.
You are both correct in the fact that we Use the honor system for recording events to general aviation aircraft , really, there's no way around that and there are many cases I have seen of poor recording and or actual cover up of potential damage. The only recourse, a buyer or owner has is to have a very knowledgeable mechanic. Research the log books and correlate to what he sees on the aircraft . if there is any doubt, just do the A. D and get the piece of mind as well as documentation that there are no detectible defects. My current view of the FAA is that they are very ineffective if only reactive at this point based on personal experience as well as current events in the industries. And I don't see this trend going in the right direction
Carl
48 yrs A/P IA DAL aircraft inspector. 172N
Hi Carl thanks for the input.
A few things of note.
Mike I'm not sure what the criteria is for being an "older thread" but correct me if I'm wrong the AD is required for aircraft having reached either 5000hrs TTIS or 5000hrs factored. It is therefore feasible that there are a number of aircraft every year that will be captured by this AD so it's going to be a topic for discussion for quite some time. Would you agree?
Carl from my aviation experience I learnt quite some time ago that the FAA started outsourcing their services to delegates for engineering and most likely other surveillance activities.
I guess the burning question I have for owners who own or about to buy, relatively speaking, a low time Cherokee, would they still carry out the AD and why?
Cheers
You're correct and stating that this will be an ongoing issue with all the affected cherokees For every year. There will be new groups of aircraft that fall under the AD either total hours or factored hours. The problem I'm trying to deal with right now is the fact that the people the write airworthy Distractives are probably the least qualified people because they never worked on the airplanes . I'm dealing with that a much larger environment.
As I mentioned, you have to correlate log books with what you see on the airplane, especially if it technically is not do yet, we've had several ownetson our field do the ad prematurely with no issues. Yes, you can cause issues by improper bolt removal. The biggest problem with the NDT which is something I do at work, is if you have corrosion or scoring in the bore that makes it hard to distinguish a defect from the background noise. On some aircraft, it could be a Crap shoot. There's no easy answer and each aircraft. I would say is it's own. Particular case to analyze
Carl
48 yrs A/P IA DAL aircraft inspector. 172N
Continuing the intermittent discussion on this topic, which has understandably gone dormant pending further direction from the FAA.
Mike, in relation to your question about fastener redundancy, my purely speculative response is that the problem in question has very little relation to the number or sequence of bolts. The photos suggest that the failure mode totally circumvents any redundancy offered by the additional rows of bolts, unfortunately. The crack propagates across the width of the spar, inboard of the other bolts. Therefore, when the crack completes, the wing separates with all the outboard spar fasteners still securely attached to the now-separated portion. Please, someone feel free to correct me if I am way off base with my understanding of this.
Barneyw, a conundrum indeed. The non-zero risk of a spar crack has to be weighed against the non-zero risk of a false positive and the non-zero risk of inducing secondary damage and bolt hole wear from the inspection itself.
Importantly, with regard to the eddy current inspection, do we have a firm (or even loose) handle on the number needed to "treat" vs the number needed to "harm?" I'm no aerospace engineer, but in medicine, we have learned the hard way many times over that shotgun, blanket, and "common-sense" approaches to testing tend to do more harm than good when analyzing outcomes on a population level.
(As an aside: A couple of you in this thread helped me out with my NLG incident a couple months ago, at which time I had considered stepping away after it was totaled by insurance... well, a month later, I decided I had stepped away long enough lol. Under contract for a Turbo Arrow III with TTAF 3200 and FSH < 200, which is what led me to this thread.)
Welcome back! 😀
Jim "Doc Griff" Griffin
PA28 - 161
Chicago area
Good choice @traumamed 😄
Karol Zadora
PA28RT-201T Turbo Arrow IV
Seattle Area
Welcome back!
Eric Panning
1981 Seneca III
Hillsboro, OR (KHIO)
Regarding "doing the AD early" with regard to the eddy current inspection.
Recently a friend did the AD on a PA28-161 200 hours early, and was given an AMOC from the FAA. The general rule seems to suggest that you should be in the window where 90% of the specified "life" should have passed. Otherwise, you will need to do the eddy current inspection again after the defined service life interval.
John Schreiber
A&P, IA, CMEL
978mhz.com
I'd be very interested to see why and what the AMOC was for. You are under no obligation to perform a AD before any specified time , thats owner discretion... Carl
48 yrs A/P IA DAL aircraft inspector. 172N
I believe I posted this comment previously (more than 3 years ago) but pulling those bolts from the wing spar DOES impact the integrity of the wing. Previous ADs and, as I've read, a few of the subsequent accidents were attributed to the removal of those bolts which compromised an, otherwise, sound wing spar.
Take a look at this recently released service bulletin.
Is this Piper suggesting a lifetime limit or am I misreading? thinking of buying a PA-32 with 8000TTIS (wing spar AD’EC test performed and passed) and curious to know if it’s got 4000 hours before getting turned into a Coke can. (not that I’m likely to live long enough to see it)