Not really new news, the
preliminary NTSB Report dated December 19th states
Preliminary metallurgical examination has located evidence of fatigue cracking in the lower rear wing spar cap, along the lower wing skin, and on an internal z-stringer. Additional evidence of fatigue cracking has been noted in the corresponding area on the left wing.
Does anyone know, from which material the lower spar flanges are made on a Mallard ? I suppose it is some corrosion resistant type from the 5000 or 6000 series of aluminum alloys. These are not really good with respect to fatigue, while most of the alloys with good fatigue properties are prone to corrosion.