Stall is the condition of insufficient lift for the aircraft weight (mass at 1g) which is approximately the angle of attack which generates maximum lift. It can only be associated with speed for specific conditions (stall speed), but there is little point in using speed in understanding stalling and recovery.
Stall warning (before the stall) and identification (at the stall) are normally generated by angle of attack so the condition can be identified irrespective of manoeuvre, weight. There are also changes for configuration.
Conventional wing stall is usually separated into level flight or turning flight (accelerated stall), and in rare circumstances problems of transonic flight (shock stall), which should not have any significant affects for commercial aircraft due to certification requirements.
The stall condition can be affected by wing ice contamination and in general is only an issue if the anti-icing systems fail; although most modern aircraft will adjust the warnings when anti-icing systems are being used.
Wings can generate lift beyond the stall angle, but insufficient for level flight. The main problem in this region of flight is maintaining control, thus it is best avoided, where recovery is to reduce the AOA by moving the stick forward. In many commercial aircraft, or those with particular problems, stall identification is supplemented by a stick pusher to direct the pilot to the correct course of action.
The conditions beyond the stall AOA are referred to as ‘deep stall’ and often confused with 'locked in stall' which is normally reserved for situations where the elevator control becomes ineffective and the stall might be unrecoverable. Although not impossible, most commercial aircraft will not suffer from this. A similar condition can be encountered at AOAs greater than stall where the pitch control is held back (also depends on trim, cg), thus preventing a reduction in AOA, but with correct procedure the aircraft should recover.
Modern aircraft with electronically signalled controls avoid the stall by pitch-control (AOA) limiting or increasing control force, but have similar characteristics if aspects of the system fail.
Another form of stall is ‘tail stall’ which should not be associated with wing stall even though the aerodynamics of loss of lift is similar. Because tail lift acts opposite sense to the wing, the symptoms of and recovery actions for tail stall are totally different. Tail stall in normal flight conditions – not in icing, is extremely unlikely due to certification requirements.
Some aircraft in rare icing conditions – where the tail will accumulate ice more quickly than the wing, can suffer tail stall, but this too is minimised by certification, but not every icing condition can be specified.
Tail stall is normally associated with lowering flaps (at the higher end of the speed range) which demands more tail ‘down’ lift. If the tail lift is already reduced by ice then the lack of lift can result in an uncontrolled and often rapid nose-down pitch change.
Recovery action is aircraft type dependent, but generally involves a rapid and forceful back-stick input and raising flap.
The Colgan accident was associated with wing stall in icing conditions, but misidentified as tail stall (fatigue, recent training on tail stall, etc) where the recovery action taken was opposite to that required.