Its written in the AD you linked:
(2) Before further flight after completing the action in paragraph (g)(1) of this AD, calculate the factored service hours for each main wing spar using the following formula: (N × 100) + [T-(N × 100)]/17 = Factored Service Hours, where N is the number of 100-hour inspections and T is the total hours TIS of the airplane.
Something seems wrong with this formula... Is the FAA saying inspections and not time are making our planes less safe? because that's what the math says.
My privately operated 1986 PA-28 with 200 hours per year and a 4 lapsed annual every year resulting in 25 inspections in 33 years has a factored service hours of 2647.
My privately operated 1994 PA-28 with 200 hours per year over 25 years receiving only annuals has a factored service hours of 2647.
My for hire 1994 PA-28 with 200 hours per year that spent the first 10 years privately operated receiving a total of 40 inspections has a factored service hours of 4058.
My for hire 1994 PA-28 with 200 hours per year over 25 years receiving both annuals and 100-hours has a factored service hours of 5000.
My for hire 2002 PA-28 with 250 hours per year over 16 years receiving both annuals and 100-hours has a factored service hours of 5000.
Note the oldest plane is 33 years old is 8 years older than the next 3 and 16 years older than the last plane but it has the same or lower number of factored service hours in its life span despite having the same total number of hours as the 1994.
The newest plane is 8-16 years younger than the other 4, has flown 1,000 less total hours in 16-17 years of service at only 4000 hours but has a factored service hours that is 25% higher than actual time flown which is nearly double the factored service hours of the plane that is twice its age and has 1000 more flight hours.
For that matter, if I fly my privately operated 1994 PA-28 for 5000 hours and have 0x 100 hour inspections done and then sell my plane to a flight school who immediately does a 100 hour in order to put it on their flight line, the factored service hours immediately jumps to from 2647 to 2741 hours without having actually flown a single hour more, all because an additional inspection was performed.
All of this because of a PA-28R that had an inflight wing separation resulting in a deadly crash during a commercial checkride at a school that was on an Approved Progressive Maintenance Plan so it isn't even doing 100-hour inspections.
I also read that the NTSB has attributed the accident to metal fatigue of a bolt which affixes the wing to the aircraft. That said bolt showed no sign of visual corrosion or pre-existing damage and that cracks in the same bolt in another PA-28R owned by the same school and identified as potentially at risk were only detected thanks to eddy current inspection which involves observing the electromagnetic properties of a surface for minute disruptions in the flow of current to find microscopic cracks and impurities.
Based on the fact the FAA is trying to rake the airframe over the coals. You can try and act like it won’t do anything, but you and I both know that if you try and sell your plane and it has not received this AD inspection, any buyer with more brains than money would balk.
The FAA has tried before and this isn't the first PA28R to have an inflight wing separation. It happened back in the 80's or 90's I think but no one could conclusively determine the precise cause of the wing separation (which is still the case with this latest incident; they know the how but not the why) nd a lack of further findings in inspections to comply with an AD issue at that time, the AD was ultimately rescinded.
NTSB has weighed in on the proposed AD - they are suggesting a much smaller footprint of aircraft in scope - Removes every fixed gear, 4 cylinder PA 28. Also they mention the risk of the bolt removal vs. the potential gain from the inspection. Lastly, they point out some of the limitation of the FAA formula.
So Piper is against it, NTSB is against it, except in limited circumstances.. I really hope this gets modified and cools the hype.
Again the cracks found on this bolt are so microscopic it takes eddy current inspection to find... Stressing the bolt with metal on metal hits with a wrench or other tools and torquing of the bolt in removal and reinstallation, seems like a sure fire way to create microscopic cracks to me.
