The National Transportation Safety Board, NTSB, publishes a report that summarizes the causes of aviation related accidents including fatigue, distractions, medical fitness and substance impairments. The data from 2008 and 2014 indicates that loss of control in flight continues to be the biggest killer in general aviation, accounting for nearly half of fatal fixed-wing general aviation accidents. The accidents resulted in 1,194 fatalities.
The NTSB views a loss of control accident as involving “an aircraft’s unintended departure from controlled flight.”
The NTSB pointed to multiple reasons for loss of control in-flight, such as pilot distraction, loss of situational awareness or weather, but said the most common type involves a stall. They indicate this may be happening because “a pilot lacks understanding about how a stall relates to exceeding a wing’s critical angle of attack (AOA), as opposed to the more common idea that it’s just related to airspeed.”
And although LOC accidents occur during all phases of flight, the NTSB notes that statistically, the approach to landing, maneuvering, and initial climb are the deadliest for LOC accidents.
You can learn more at the NTSB website: http://www.ntsb.gov/safety/mwl/Documents/2017-18/2017MWL-FctSht-LossControl-A.pdf