All Dutch registered Zenair Zodiac CH601 XL aircraft grounded.
According to this Dutch language website the Dutch aviation authorities grounded all twelve Dutch registered Zenair Zodiac CH601 XL aircraft until further notice.
A Zodiac CH601 SL crashed last September in The Netherlands, after one of the wings ‘folded upwards’, killing both occupants. Apparently, research showed that since 2006 at least seven aircraft of this type crashed due to a similar failure mode.
Investigations of these accidents, including the one in The Netherlands, so far didn’t result in determining the exact cause, but according to the above website the Dutch aviation authorities appear to have some evidence pointing to structural deficits…..
We’ll keep you posted on how this issue unfolds…..
EDIT: since writing the above lines I’ve searched the internet for builder weblogs to learn how the wing is constructed. I’m speculating here, but compared to other aluminum wing spar structures I’ve seen, the main spar shear web between the upper and lower spar caps at the wing root doesn’t look ‘over-engineered’. I would have expected tighter spaced vertical compression columns to prevent shear web buckling, especially so in the wing root area.
Other reports speculate that flutter (caused by aileron control cables that aren’t tightened up enough) might have put enough energy into the wing that the spar failed at the wing root. Zenair Europe even put out an AD (Airworthiness Directive) that summons 601XL owners to - among other things - inspect for control cable tensioning and for rivet damage in certain critical areas.
Are these seven accidents caused by spar shear web buckling at the wing root, perhaps by a higher than normal loading induced by flutter? We’ll have to wait until the accident report is released…..