The NTSB found that the crash of an Embry-Riddle Aeronautical University Piper PA-28R-201 that killed two people in April 2018 was caused by extensive fatigue cracking in the left-wing main spar, according to the final report (PDF) issued by the board on Tuesday. As previously reported by AVweb, the left wing separated from the aircraft shortly after a touch-and-go at Florida’s Daytona Beach International Airport (DAB). A second ERAU Piper was found to have a similar fatigue crack in its left-wing main spar when the school’s fleet was examined after the accident. The board noted that no anomalies in materials or construction of the wing spars were found on either aircraft.
“The NTSB concludes that, due to flight training maneuvers, significant operation at low altitudes, and frequent landing cycles, the accident airplane (and its sister airplane in the operator’s fleet) likely experienced landing, gust, and maneuver loads that were more severe than expected for training aircraft,” the NTSB said in its summary (PDF) of the report. “Therefore, the low-altitude flight training and frequent landing environment likely resulted in the accident airplane accumulating damaging stress cycles at a faster rate than a personal use airplane.”
The NTSB reported that the accident aircraft had accumulated 7,690.6 hours and 33,276 landing cycles prior to the crash, averaging 4.33 landings per hour of flight time. The board also found reports of reported flap extension overspeed, gear extension overspeed and hard landing events in the aircraft’s logs, but noted that airframe inspections had been performed after each event with no defects noted.
The NTSB further established that, due to its location, the fatigue cracking would not have been visible from either the interior or exterior of the airplane. In response to the potential for such cracking to go unnoticed, the FAA issued a notice of proposed rulemaking (NPRM) eight months after the accident which suggested required wing spar inspections for nearly 20,000 Piper PA-28 series aircraft. The NTSB said it had “expressed … support of the proposed AD’s inspection requirements but urged the FAA to reexamine the proposed AD’s applicability to certain airplanes based on airplane usage.” Comments closed on the NPRM in February 2019, but an AD has not yet been issued.
The very FIRST question I’d be asking of any airplane found to have cracks is … where were the spar extrusions manufactured? I’d be willing to bet that they were built by a low bidder and possibly overseas? I’d also bet that more newer airplanes will be found to have the problem than the good ‘ol older ones that’ve been flying for years without issues … except for airplanes like the pipeline patrol high time machine. Beyond that, since it’s obvious the cracks are around drilled rivet holes, I’d wonder about the manufacturing and QA processes in work there … especially if it’s only newer airplanes. But all that’s just my guess.
As usual, in the name of “safety,” thousands of PA28 owners will face the heavy hand of our friends who are here to help.
As I recall, the cracks developed in the locations of drilled attach-BOLT holes. Which begs another question: why not a staggered bolt pattern?
And I have to ask:
By the time a student gets promoted from Warriors/Archers to Arrows, shouldn’t harsh landings be a dim memory?
Yars … I said rivets but meant bolts. Good catch. Mea maxima culpa.
At a remanufacturing facility I visited last summer, I got to see wings from all the models of Pipers. The heavier the airplane, the heavier the spars but the design is essentially identical. They did eddy current inspection on all serviceable wings and only found one with questionable results.
I’d be interested in knowing if that failure location was adjacent to the dihedral bend of the spar? I noticed a Mooney tube frame example at Airventure 2019 where they obtain dihedral from the wing carry through box and not the spar itself. Maybe that’s something that needs visiting? If the metallurgy wasn’t up to the task and a bend was made … uh oh !! And that a similar age airplane with similar usage pattern also had an issue is — likewise — worrisome.
Larry, may I suggest if you have not already, read the NPRM, gives excellent overview of the location. of the bolts/attach areas PLUS, there is a wealth of parts and MM on Pipers available on the web to educate you and others on the location and specifics of the spar attach to the box. Now listen up all, its not just flight issues the may cause cracking loads on the attach areas. How many Cherokees have been driven off road, wings removed for transport then reattached back at the hanger. LOTS. Just the act of R/R of the wings can induce damage to the bolt holes. Ive seen it. Go ahead, pound out a bolt on a 30 year old plane and see what the hole can look like. I don’t think this is a manufacturing issue at all but unfortunately, it is a issue.
The test of the spar materials revealed no anomalies. And hard landings can happen to anyone, at any number of hours. The first few in a new plane can certainly be problematic. When you have 33K landings, even if 90% were good, that leaves a whole bunch of wing flex events.
That’s 4.7 landings per hour – in an Arrow??? Doesn’t account for much cross-country time, or instrument training time. Actually, it sounds like a lifetime of touch-and-gos. In an Arrow? WTF is ERAU doing?
Over 7 thousand hours of training, Low wing (with the main gear mounted to wing), plus Florida corrosion. Honestly it’s not too much of a surprise.
Corrosion doesn’t seem to be the issue. The accumulative stress from 33K landings, overspeed gear and flap extension, etc. can certainly be an issue. Only one other plane exhibited cracking. It will be interesting on how the final AD will read. The NTSB wants inspection based on type of usage, which actually makes sense. Training planes get hammered. The difference between the 172 I trained in and the one that I bought was quite noticeable.
Sorry, I was mentioning the top 3 reasons why “I” was not surprised. 106ER met all three reasons why “I” would not buy that plane. I’m sure the flight school was already pretty close to rotating that plane out of their fleet…. to the used market.
The Piper Cherokee Six has hauled as many tons of freight, cargo and passengers as any aircraft in Alaska. Some of the very first Cherokees built are still flying heavy loads everyday to/from remote communities with unimproved landing strips. A less than 8000 hour commercial Cherokee in Alaska is unheard of…. try 20,000 plus hours on the average.
During an Inspection Authorization (I.A.) annual meeting the topic of “Unapproved Parts” was discussed. An I.A. in attendance asked “Who is inspecting the parts outside the United States?” The answer was “The FAA only has permission to oversee parts manufacturing in a few countries.” Follow up question was “What is the difference between an “Unapproved Part” and a part without FAA oversight?” Answer: “NONE”.
The “Aviation Manufacture Liability Reform Bill” was signed into law in the late 1990’s. Included in the liability reform bill was a stipulation that a percentage of parts were manufactured outside the United States in order to help the developing countries.
The amount of metals and the way they are added to an aluminum alloy is just as critical as the tempering process. Ask any engineer when they’re designing a structure how important the materials strength and brittleness is?
Klaus and Diego below … the question of the spar’s integrity vis-à-vis metallurgy is exactly something to be concerned about. I’d sooner buy an old Cherokee than a new one.
I think the FAA report implies 33,000 landing cycles was the cause, not flight hours. I doubt you AK Cherokee Six has anything close to that.
One of the nice aspects of extruded parts is the ability to clip a “coupon” from each instance, for testing. Well worthwhile, for critical parts.
Our facility performs Maintenance to an old flight school Cherokee 140. It has 46,000 + hours, all of them on pre-solo since new, first in Bogota’s GYM AirPort @ 8,400 ft (higher ground speed touch down) and now in Bucaramanga @ near 4,000 ft. Since there’s no special structure programmed inspection or AD, We decided it was time to perform a complete NDT inspection just for peace of mind. We did it at 45,000 ACTT involving the whole plane, wings, tail etc…so we disassembled completely.
Nothing found. If we consider this plane mostly was used for touch and go, not cross-country time, it accumulates near 250,000 landings, and lot of hard landings.
Here in Colombia our authority is pursuing “good old planes” more than 40 years, (not flight time or environmental conditions), for “safety” as well, and my question is, does the new ones are as safe as our rulers claim?
I think the old USA manufacturing was superb, didn’t know newer planes spars are manufactured overseas, not good news for me….
The 140 is considerably lighter than the retractable gear -28R; but then again, it only takes one really hard landing to hurt an airplane.
Wikipedia: “On 1 May 2009, American Capital Strategies sold the company to Singapore-based investment strategy company Imprimis, making a profit of US$31 million on the sale. Imprimis is funded by the Government of Brunei and has offices in Bangkok, Singapore and Brunei Darussalam.”
https://www.avweb.com/news/piper-has-been-sold/
The person holding the purse strings will decide what can be mitigated to save the most money. Notice how silent the Vero Beach officers are on the topic? Most likely the lawyers told them to shut up and weather the storm…..
Well … I had both a PA-28 and a C172 in my hangar … and one of ’em had to go. The Cessna is still there … after 35 years with me. Each had plusses and minuses but the Cessna had more + than – for me. This “problem” solidified the decision. Beyond that, ease of ingress / egress and cabin size were predominant decision points.
Airstair doors are pure genius for us -ahem – “senior” pilots.