Checkout_my_Six
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Gonna have to add em up....
Possible new AD for Piper PA28's
- Thread starter Marky_24
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This might be a stupid idea, but especially considering the PA28 is still in production is there any chance of a redesign/modification to strengthen the problem area?
Or use a progressive inspection?
SoCalPilot88
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SoCalPilot88
If the investigation reveals the design is insufficient, or if cracks are found in the fleet, the I-beam construction of the spar looks like it could accommodate an angled bracket at the fracture region. It would need to have a compound angle. The reinforcing bracket would transfer the load of the five existing bolt holes to the wing spar via additional holes drilled in the spar.
However, this design is stout and has had very little failures over the decades. If this was manufactured per the design requirements, and the aluminum material is heat treated properly with no inclusions or other flaws, there should be no reason to suspect this region of the wing unless there was a known overload condition.
drotto
Cleared for Takeoff
It is also a 60 plus year old design. It has (if I remember correctly) 2 reported failures outside of failures that were determined to have occurred because the airframe was overloaded due to pilot error. I found that about 33000 various PA28's and about 7800 PA32's have been built. So around 41000 planes have this wing spar setup, and who knows how many flight hours. That is a 0.005% failure rate that can be attributed possibly to the structure and was outside of pilot control.
In my mind that is a very reliable design.
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kgruber
Final Approach
You could design a wing strap and get an STC, like Saunders did for the King Air, and Beech copied.
"""Spar Straps
Way back when, there was some concern about wing bolts in the 90 series King Airs, and it was handled in a similar fashion to the 200s. Around that time, Dave Saunders of Avidesign, who had designed spar straps for a variety of aircraft, came up with a spar strap STC for older King Airs (if this sounds familiar, it was discussed in Tom Clements’ article in the December 2015 issue of King Air). It was marketed as an added safety feature and became popular enough to prompt Beech to design their own spar strap for the 90 series. Bear in mind, it was not required equipment, it was an option. There are plenty of 90s, many of them 30 or 40 years old, still flying safely without spar straps."""
http://www.kingairmagazine.com/article/wing-bolts/
"""Spar Straps
Way back when, there was some concern about wing bolts in the 90 series King Airs, and it was handled in a similar fashion to the 200s. Around that time, Dave Saunders of Avidesign, who had designed spar straps for a variety of aircraft, came up with a spar strap STC for older King Airs (if this sounds familiar, it was discussed in Tom Clements’ article in the December 2015 issue of King Air). It was marketed as an added safety feature and became popular enough to prompt Beech to design their own spar strap for the 90 series. Bear in mind, it was not required equipment, it was an option. There are plenty of 90s, many of them 30 or 40 years old, still flying safely without spar straps."""
http://www.kingairmagazine.com/article/wing-bolts/
Silvaire
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Better keep quiet. I think the 28-181's got left out at first but they are in there now.
I really don't yet understand how this works for a plane that has been used for flight training, but the logs mostly show an annual inspection, not a 100 hr inspection.
I'll use my PA28-181 as an example.
There are a total of 53 annual or 100 hr inspections in the logs. The plane was mostly used as a trainer, but the logs show only 14 100 hr inspections and 39 annual inspections. I looked through the title history and overlayed that with the annual completion and have at least 13 real annuals to private owners, which could leave a potential of 40 100 hrs. total time is 4771.
According to the formula, how many calculated hours do I have?
(14 x 100) + (4771 - (1400)/17= 1598 hrs
or
(40 x 100) + (4771- 4000)/17= 4045 hrs
Either way I am under the limit, but the calculated time is dramatically different. Even at the higher number, I have 16,235 more personal flight hours before I hit the 5000 mark.
I'll use my PA28-181 as an example.
There are a total of 53 annual or 100 hr inspections in the logs. The plane was mostly used as a trainer, but the logs show only 14 100 hr inspections and 39 annual inspections. I looked through the title history and overlayed that with the annual completion and have at least 13 real annuals to private owners, which could leave a potential of 40 100 hrs. total time is 4771.
According to the formula, how many calculated hours do I have?
(14 x 100) + (4771 - (1400)/17= 1598 hrs
or
(40 x 100) + (4771- 4000)/17= 4045 hrs
Either way I am under the limit, but the calculated time is dramatically different. Even at the higher number, I have 16,235 more personal flight hours before I hit the 5000 mark.
Tom-D
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I'll believe when the final version of this AD is written, you'll have 229 hours until your aircraft hits the magic mark.
Admittedly, I only scanned the proposed AD but as I interpret it the FAA only weights the 100 hour inspections negatively in the current writing of it. There will be shops/schools who will use this to their advantage; it will be up to you and your mechanic on how you want to proceed with your plane.
bflynn
Final Approach
Actually, better to speak up. We're talking about a hull design flaw which can make the wings fall off. It's a minor chance, but they found it in two airplanes at ERAU. If you have a PA-28, high time or not, I would think you'd be very, very interested in what's going on.
Just a reminder, wings falling off airplanes usually results is a bad ending. Ok, if you're a F-14, maybe you can fake it, but a PA-28 is not a F-14.
Not quite. It's not "53 annual or 100 hr..." Only 100 hr inspections. Most aircraft have an inspection done every 12 months (1 inspection annually). If an aircraft is used for compensation (training) then an inspection is due every 100 hours of operating time which could be once a week for the same 12 month period (52 inspections annually). The feds are trying to separate aircraft into groups based on individual 100 hr inspections and not annual inspections. But still too many variables to their AD plan to make a call as an "annual" sign-off is not technically a "100hr" sign-off.
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Lantraxco
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OldNewbie
High wings spread the shock loads through the braces from a wider leverage point, can't speak to the engineering math but it's something to keep in mind. With the low wing, one attaching point is all ya got. Another thought is the low wing Cherokee, et al., has the attaching points for the wings to spar box down in the muck, which may mean moisture, maybe salt, maybe deicing fluids can find their way in, all of which may contribute to corrosion which can accelerate fracture and failure. Of course maybe it's just that the hotshot young CFI's don't think it as cool to do illegal aerobats in a Cessna as it is in a low wing kite?
Tom-D
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Getting back to the AD:
As I understand the intent of this AD, it basically requires pulling the wings, and inspecting the area around the bolt holes and the size of the holes, attaching the wing to the spar carry thru.
this does not sound cheap or quick.
As I understand the intent of this AD, it basically requires pulling the wings, and inspecting the area around the bolt holes and the size of the holes, attaching the wing to the spar carry thru.
this does not sound cheap or quick.
Not necessarily. They make a number of specialized EC probes to inspect bolt holes as installed. They can pull one bolt at a time, check the hole, then reinstall the bolt. And so on. The AD only requires the lower spar cap bolt holes to be inspected. The main problem will be getting the bolts out.
Tom-D
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not when they are loose
Tom-D
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my comment was submitted.
Comment:Appendix 1 to the AD requires methods in excess to find cracks in this installation. requiring Eddy Current inspections by certified personal removes this AD from the capability of most A&P -IAs that do the annual or 100 hour inspections on aircraft not in training school environment.
Having certified persons with the equipment to complete this inspection will add expenses that are not considered in the cost computed by the FAA.
Secondly the complicated method of computing which aircraft this inspection will include will cause great confusion, when the standard of Total time on the Airframe will be just as effective. By placing the time requirement on the wing beam in all practically places a time life on the wing.
Comment:Appendix 1 to the AD requires methods in excess to find cracks in this installation. requiring Eddy Current inspections by certified personal removes this AD from the capability of most A&P -IAs that do the annual or 100 hour inspections on aircraft not in training school environment.
Having certified persons with the equipment to complete this inspection will add expenses that are not considered in the cost computed by the FAA.
Secondly the complicated method of computing which aircraft this inspection will include will cause great confusion, when the standard of Total time on the Airframe will be just as effective. By placing the time requirement on the wing beam in all practically places a time life on the wing.
drotto
Cleared for Takeoff
I actually disagree that tt is just as effective. The FAA is clearly trying to separate commercial flight school use from personal use aircraft. Flight school aircraft are used much harder and each hr of tt is not equivalent. A personal plane will mostly be doing point to point flights or local sight seeing. This involves 1 take of and landings per flight. For arguments sake this is 1 cycle per hour of flight time.
With my own plane I have done maybe 3 in an hour, but rarely do I just stay in the pattern and repeat cycles rapidly.
In a training situation it is not uncommon for pattern work where you can get as high as 6 maybe even 8 take off and landings per hour. That is 6 cycles, and the stress on the airframe for that 1 hour of flight time is not equal.
The 100 hr part of the equation is the most realistic statistic in the log to determine if a plane has ever been used for commercial purposes (I know is can be manipulated, and they will need to look into that). I personally think the divided by 17 part of the equation may be a bit generous ( do not kill me for that), and perhaps that number should be more in the 10 to 15 range. But I applaud the FAA for attempting to not financially kill private owners and risk partially grounding what has historically been a great airframe.
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hindsight2020
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Agreed. And not "has been", it is a great airframe. That Embry Riddle decided to socialize losses like the greedy piggies they are, does not take away merit from the airframe and thankfully in this case the FAA has found some modicum on nuance (even a blind squirrel finds a nut every now and again).
I've owned two PA-28s in my tenure in this hobby and have been delighted with the dispatch reliability and ease of airframe and engine mx of the type. The embedded opportunity costs is that it is popular with flight schools and as such we eat the losses when one craps their pants... and we all get told to wear diapers.
drotto
Cleared for Takeoff
I also would add to be previous statement, that if you count just tt as was suggested about and apply that "logic" to the FAA equation, it would mean that at about 5000 tt all PA28's would be required to have this possible invasive spar inspection. That would in effect be putting a 5000 hr lifespan on the plane, if the costs to inspect are in fact onerous.Agreed. And not "has been", it is a great airframe. That Embry Riddle decided to socialize losses like the greedy piggies they are, does not take away merit from the airframe and thankfully in this case the FAA has found some modicum on nuance (even a blind squirrel finds a nut every now and again).
I've owned two PA-28s in my tenure in this hobby and have been delighted with the dispatch reliability and ease of airframe and engine mx of the type. The embedded opportunity costs is that it is popular with flight schools and as such we eat the losses when one craps their pants... and we all get told to wear diapers.
Again, the FAA is not looking to ground a plane that has 33000 aircraft, but only 2 failures, and I think they found 1 other plane with cracks.
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Tom-D
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See ? already much confusion, and personal opinion inserted in how to read what the FAA intends
Tom-D
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No one is arguing how great an aircraft the PA-series are.Agreed. And not "has been", it is a great airframe. That Embry Riddle decided to socialize losses like the greedy piggies they are, does not take away merit from the airframe and thankfully in this case the FAA has found some modicum on nuance (even a blind squirrel finds a nut every now and again).
I've owned two PA-28s in my tenure in this hobby and have been delighted with the dispatch reliability and ease of airframe and engine mx of the type. The embedded opportunity costs is that it is popular with flight schools and as such we eat the losses when one craps their pants... and we all get told to wear diapers.
Tom-D
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We all know that the high time aircraft are the ones the FAA is worried about because they are the ones most likely to be the the ones in training environment. Lots of CFIs teach in their own aircraft then rent it to their students, Renting is not considered a commercial activity. but will put as much stress and time as a flight school.
Plus many of these aircraft get an annual at 100 hours, even when the inspection occurs at 8 months.
Put a 1 time inspection on all A/C that have 5000 hours, then reduce it to at annual check for looseness.
simtech
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Going through my logs Ive found a few "100 hr" used in place of an annual when clearly its been a year and not even 100 hours passed. Yay me... My plane was never a trainer but was in a club way back when.
The one item that is not very prominent in this discussion is that this will be the 2nd time an AD is issued, the 2nd time wing spar times will be factored, and the 2nd time the Feds/Piper are trying to segregate aircraft by operation type on the PA-28 family. The 1st was in 1987 when a pipe-patrol aircraft had a lower spar cap failure in flight. At that time the trigger wasn't 100hr inspections but aircraft that operated at 1000' AGL continuously.
AD87-08-08 required the wings removed for a spar inspection at the magic 5,000 hr mark. However, after 500+ inspections no more cracks so the FAA suspended the AD and the inspection went back to the SB level. The docket lists 2 previous Piper SBs (which are linked in post #35) that explains this more.
I'd recommend those PA aircraft owners possibly affected to enter a docket comment in favor of a more reasonable inspection that can be accomplished at field level by an A&P like fluorescent dye check or a 10x visual of the bolt hole area with the bolt removed. And while I like the factored approach to this inspection too many variables exist to make the current formula workable. Maybe a straight X+Y=Z factor based on ownership type may work better or the number of total inspections per year as a factor with 1 per year being the control or base to calculate from.
Just remember how important those fuel selector decals were recently.
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drotto
Cleared for Takeoff
I had forgotten about the previous AD that was suspended. I knew about the 87 crash
. The FAA is trying to avoid a repeat of the AD, realizing that a previous 5000 tt inspection directive was pointless.
There seems like there is a way to change the formula so all inspections are counted not just 100 hr. That is reasonable. That will hit older airframes hard, but you can argue that is logical.
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Tom-D
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All of them, the annual retirement does not go away just because it had a 100 hour.
Tom-D
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Progressive inspections still must be completed each year.
True. But the context of that comment and the one responded to was if an operator signed off all their inspections as "annuals" or used a progressive inspection there would be no "100hr inspection" history in the aircraft logs as specifically defined in the proposed AD.
Tom-D
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This is why A/F TT is the only way to sort out the loose wings. One time inspection on all PA-28 with over 5000 hours.
Checkout_my_Six
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disagree....Tom.
landing cycles causes fatigue....not total time.
landing cycles causes fatigue....not total time.
Tom-D
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Checkout_my_Six
Touchdown! Greaser!
no....that's not correct.
Tom-D
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For this purpose it certainly is.no....that's not correct.
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Hang 4
I’ll bite, how do landing cycles get counted?
drotto
Cleared for Takeoff
For small planes they aren't, that is the issue here. The high landing cycles are the likely cause of the failure. With this equation the FAA is trying to estimate landing cycles.
The most reliable statistic they could find that would predict if a plane would have higher landing cycles is if it had been used for commercial purposes, and in the case of the PA28 this would be as a trainer. They are assuming training planes have more landings. By assessing if the plane was used as a trainer ( using the 100 hr inspections), the FAA is saying that plane will have increased landing cycles. The more 100 hr inspections, the more use as a trainer, the more landing cycles. Thus more stress on the wing spar and a higher chance of failure. Thus a PA28 used as a trainer is going to have harder hrs than a private plane.
The 100 hr is being used to estimate landing cycles, because they have no better way of doing it. Unlike commercial jets, we have no recorded cycles. It is imperfect, and will likely miss high cycle planes that private owners used a lot in the pattern, as well as club and CFI owned planes that have been used often for training, but may not have been subjected to 100 hr inspections.
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