It took long enough, but the FAA has finally issued an airworthiness directive (AD) warning the aviation industry about the potentially defective slat tracks installed on some Boeing 737 aircraft. Boeing announced the problem over a week ago, and the FAA remained silent until yesterday, prompting questions about why it wasn’t taking action.

Reports so far indicate that the defective slat tracks, which control the forward flight surfaces of the 737’s wings, were manufactured by a supplier to Spirit AeroSystems, and then sold to Boeing. Boeing, Spirit and FAA have refused to name the supplier, which is causing a bit of an Easter Egg hunt by aerospace professionals.

In my prior article, I suggested two possible candidates: Drewloong Precision from Taiwan, or Aubert & Duval in France, the latter of which had both its AS9100 and Nadcap certifications withdrawn just prior to Boeing’s announcement.

An Oxebridge reader pointed out that lists the Belgian company ASCO as a slat track manufacturer for Boeing, selling through Spirit AeroSystems, but two representatives from that company claim that ASCO has not been notified of any quality defects in its slat tracks, whether from Boeing or anyone else. But ASCO would have reason to keep this quiet: Spirit has just launched a  new bid to acquire ASCO entirely, and any news of defects escaping their plant would impact on the acquisition deal. If it is ASCO, then both Boeing and Spirit have reasons to keep it quiet until after the merger, and FAA is just dutifully following Boeing’s lead, as usual.

The FAA AD does point to a bit more detail in the nature of the defect, saying the slat track parts “were manufactured incorrectly and are affected by hydrogen embrittlement.” This points to a special* process which, again, is what seems to be at the heart of Aubert & Duval’s problems. Many readers have said their Spidey-senses are telling them A&D falsified special process test data, and either accidentally or intentionally released defective parts. But the dots are still very far apart, and can’t be connected conclusively yet.

(NOTE: Aubert & Duval has denied any involvement in the slat track nonconformities; see Update below.)

Adding fuel to the fire (pardon the anticipatory pun), FAA also released another AD, related to “significant changes made to the airworthiness limitations related to fuel tank ignition prevention and the nitrogen generation system.” This AD also targets multiple Boeing 737 models. The mainstream press has not picked up this story yet, but expect it to go viral in a day or so. The FAA has not announced which suppliers may be responsible for that problem, either.

UPDATE 12 JUNE 2019: an Oxebridge reader who is a metallurgist says the hydrogen embrittlement problem would likely be due to “failing to bake or baking at wrong temp/time after a chemical process, such as electroplating or surface temper inspection (nital etch).” I had posted that the problem was likely related to heat treat, which now appears incorrect. I am slapping myself for not realizing this, and have corrected the text of the article above.

In a strange development, searching the Nadcap database for Aubert & Duval now comes up with a “no records found” error message, whereas just the other day (June 7) I was able to pull up all their records, including those with suspension notices. It might be that I’m keying something wrong, so have written to PRI for clarification.

UPDATE 14 JUNE 2019: An official spokesperson for Eramet, which owns Aubert & Duval, has provided the following statement denying involvement in the Boeing slat track nonconforities:

We would like to point out that, contrary to what you indicate, our company does not manufacture the defective slat tracks installed on some Boeing 737 aircraft nor does it provide material that is part of their composition.

UPDATE 25 JUNE 2019:

Oxebridge has confirmed that ASCO is not the manufacturer of the slat tracks; see full report here.


About Christopher Paris

Christopher Paris is the founder and VP Operations of Oxebridge. He has over 30 years' experience implementing ISO 9001 and AS9100 systems, and is a vocal advocate for the development and use of standards from the point of view of actual users. He is the author of Surviving ISO 9001:2015. He reviews wines for the irreverent wine blog, Winepisser.