The main causes of pattern stalls are task saturation and pilot distractions.
Stall is defined as a sudden reduction in the lift generated by an aerofoil when the critical angle of attack is reached or exceeded.
A stall occurs when the angle of attack of an aerofoil exceeds the value which creates maximum lift as a consequence of airflow across it. This angle varies very little in response to the cross section of the (clean) aerofoil and is typically around 15°. At the stall, the airflow across the upper cambered surface ceases to flow smoothly and in contact with the upper surface and becomes turbulent, thus greatly reducing lift and increasing drag. Changing the effective configuration of a wing by the deployment of leading edge or trailing edge devices will directly alter the angle of attack at which an aerofoil stalls. However, all this assumes a clean wing and for any aerofoil, contamination of the normally smooth surface by frozen deposits will result in a change to the angle of attack at which a stall will occur.
The Angle of Attack of an aerofoil – the incidence of the wing to the incident airflow - is not the same as the pitch attitude of the aircraft as displayed on the corresponding primary flight instrument and many aircraft do not have an instrument which displays angle of attack. However, when flying straight and level with a particular aircraft mass and prevailing density altitude, for every wing angle of attack there is a corresponding indicated air speed. Because of this, the indicated airspeed at which an aircraft has been shown to stall in given circumstances is determined during aircraft certification and included in the AFM. This indicated speed, Vs, provides a fundamental reference for all other AFM aeroplane performance calculations which involve indicated airspeed and helps define the Flight Envelope for each aircraft type and variant.