Aircraft upset is a dangerous condition in aircraft operations in which the flight attitude or airspeed of an aircraft is outside the normal bounds of operation for which it is designed. This may result in the loss of control (LOC) of the aircraft, and sometimes the total loss of the aircraft itself. Loss of control may be due to excessive altitude for the airplane's weight, turbulent weather, pilot disorientation, or a system failure.

The U.S. NASA Aviation Safety Program defines upset prevention and upset recovery as to prevent loss-of-control accidents due to aircraft upset after inadvertently entering an extreme or abnormal flight attitude.

A Boeing-compiled list determined that 2,051 people died in 22 accidents in the years 1998–2007 due to LOC accidents. NTSB data for 1994–2003 count 32 accidents and more than 2,100 lives lost worldwide.