Owners of Piper PA-28 and PA-32 models have been hit with a series of airworthiness directives over the last year, including one related to main-spar corrosion, but the latest AD stems from a fatal accident in 2018 when a Piper Arrow conducting flight training lost a wing and killed the FAA examiner and student. The Arrow was 11 years old but had accumulated more than 7,600 hours, exclusively in the training environment.
The most recent AD calls for inspections of the lower spar caps at the bolted joint to the carry-through structure inside the cabin for aircraft with more than 5,000 hours time in service and applies to more than 5,400 aircraft. The accident Arrow’s wing failed due to a fatigue fracture at the “bolted joint” along the lower spar cap, according to investigators. The AD is effective on Feb. 16, 2021, and affects PA-28 and PA-32 aircraft from the PA-28-151 Warrior up to the PA-32RT Saratoga. It also includes all Arrow models, but not the PA-28-236 Dakota or the lighter non-taper-wing PA-28 series.
According to the FAA, “Because airplanes used in training and other high-load environments are typically operated for hire and have inspection programs that require 100-hour inspections, the FAA determined the number of 100-hour inspections an airplane has undergone would be the best indicator of the airplane’s usage history. Accordingly, the FAA developed a factored service hours formula based on the number of 100-hour inspections completed on the airplane. This AD requires calculating the factored service hours for each main wing spar to determine when an inspection is required, inspecting the lower main wing spar bolt holes for cracks, and replacing any cracked main wing spar.” In short, the inspection portion of the AD applies when any given airplane has accumulated more than 5,000 “factored service hours,” a determination that had to be made within 30 days of the AD’s implementation by reviewing the logbooks and counting the number of 100-hour inspections determined to be associated with flight-training use. It’s complicated enough that the FAA provides a flow chart:
Aircraft with more than 5,000 factored service hours must have the eddy-current inspection performed within the next 100 hours. The test is said to cost just more than $1,000 per aircraft, though a wing-spar replacement is estimated at more than $12,000 each wing. What’s more, the FAA says it will not issue ferry permits to those aircraft found to have cracks; they will have to be repaired locally or disassembled and taken to an appropriate service facility. Finally, the FAA is calling this AD an “interim” measure, suggesting that data from the field could change the minimum number of service hours.
No surprises here. Yet.
The design could be better.
As a long time owner of a PA-28 I find this AD to be more about liability.
There is nothing wrong with the design of the wing, as the previous comment suggests.
There are a few of the ‘Hershey’ bar 140’s/160/180 Cherokees in my neighbourhood that have in excess of 20,000 hours on the air frame. There is a whole lot more to the story that being said here.
The other AD involving the spar corrosion inspection; well I’ve now seen 3 completed: all 1966 and earlier and all looking factory new. The Pipers are a reliable and proven design, so what could be better??
Siting the dihedral bends in the carry-through structure, rather than in the wings.
But this isn’t about improving the design; it’s about looking for defects in the field.
Unfortunately this seems to be just the result of aging airplanes. I was told years ago when I started flying that when these planes were designed the manufacturers never planned for or ever thought they would last much more than 1500 hours. Of course the severe use or abuse from training flights doesn’t help. Even the strut braced Cessnas have been issued structural AD’s, along with some Beechcraft models. Correct me if I am wrong but I believe the Piper Tomahawk has a 10,000 hour airframe life limit, a plane designed in the late 70’s. Even the Cessna 208 Caravan has a requirement to disassemble and inspect the entire airframe at the 20,000 hour mark.
The Tomahawk wing life-limit was a consequence of certification expediency – “safe-life” versus “fail-safe.”
Its unitized main spar is built hell-for-stout, believe me.
It figures that the FAA would ignore the same mistake they made years earlier in a similar AD where the inspection procedure caused wing separations.
What’s more, they’ve also ignored that fact that the eddy current inspection requires removal of the wing spar bolts. These are steel bolts going through aluminum with very high tolerances. Do you want to be the first guy for whom the FAA says, “Oops,” when your plane falls out of the sky because they “guessed wrong” or ignored the advice of the manufacturer, engineers and countless A&Ps?
seems there has one ever been one other wing separation, on an Archer used extensively for pipeline patrol..(constant turbulence), and no reported separation of a “Hershey bar” winged version…the design of the spar web in attach point area raises questions in my mind though, there are high loads on the lower external bolt connections
As an IA, ( and plane owner) I love AD’s as much as anyone else does. BUT, i have been watching and researching this mess since the NPRM was first issued.
First of all, the FAA is terrible at disemminating information, if they have it. I came across a well done FAASTeam report done by the Orlando FSDO. EVERYONE MUST READ IT. Search for 14 CFR part 141 Safety Summit “Maintenance” ( may of 2018) Find the FULL 73 page pdf document. Damaged spars are not ISOLATED incidents. Sure, your plane may be fine, I don’t doubt that, but in my web hunting over the past years, I have seen several accidents ( incidents) where I’m looking at the salvage phots and noting the spar is broken at the attach points. The two that I found that were noteworthy were just RUNWAY EXCURSIONS. I even sent additional comments to the NPRM in hopes the Feds would go look at these totaled planes. Who knows if they did. My point is this, SPARS CAN’T fail, and if they do we need to address causes. While I’m not happy about this problem, my experience says we have a issue.