National Transportation Safety Board investigators have released a preliminary report on the June 2012 plane crash near Veneta that killed four Oregon Country Fair workers on a scenic tour.
Investigators found no evidence of engine or mechanical breakdowns but they noted the temperature and dew point at the time were conducive to carburetor icing at glide power.
The Register-Guard reports the safety board is expected to rule next month on the cause of the crash.
The report says investigators found an iPhone in the wreckage that contained video of the Cessna 172 taking off. Investigators heard a mechanical chattering sound on the video, similar to a stall warning horn.