All 20 people aboard a Junkers Ju-52 vintage propeller plane were killed when it slammed near vertically into the Swiss Alps on Saturday, reports the AP, spurring an investigation that officials are already expecting to be "relatively complex." The crash occurred near the resort town of Flims, and the plane, operated by Swiss tourism company Ju-Air, issued no distress call. Officials don't think the cause was mid-air collision, foul play, or the plane breaking up, but are hampered by a presumed lack of modern voice and data recorders. Junkers Ju-52 planes were built between 1932 and 1952 and can carry up to 17 passengers and three crew. (More prop plane stories.)