The thing that distinguishes deep stall from ordinary stall is that in deep stall the aircraft continues to pitch nose up, taking it deeper into the stall. . .. .Under normal circumstances, if both wings stall simultaneously, a straight winged aircraft will pitch nose down, taking itself out of the stall. This is because as the wing stalls, the C of P moves aft, creating a nose down pitching moment.. .. .With a swept back wing the situation is somewhat different. Spanwise flow out towards the tips produces a thick sluggish boundary layer over the wingtips. This separates more easily than the higher energy boundary layer close to the roots, so the wingtips stall before the roots. But the wingtips are further aft than the roots, so the tip stall causes the C of P to move forward. This causes the aircraft to pitch nose up taking it deeper into the stall. The loss of lift then causes the aircraft to descend, making the angle of attack still greater. The overall effect is that aircraft goes ever deeper into the stall.. .. .The position of the tailplane becomes a very important factor at this stage. A high tailplane (T-tail) is likely to be enveloped in the turbulent flow coming from the stalled wings. This will drastically reduce its effectiveness in regaining pitch control. This is why the T-tailed aircraft you referred to have particular problems with deep stall. It is also why such aircraft must have stall prevention devices such as stick shakers and pushers. With a low tailplane the turbulent flow is likely to pass well above it leaving full pitch authority available.. .. .The fact that many T-tailed aircraft also have rear fuselage mounted engines just makes matters worse. The turbulent airflow from the stalled wings is likely to cause engine surge/stall, turning the aircraft into a (very bad) stalled glider!. .. .The important point to note as far as the JAR ATPL exams go is that it is the tip stall of the swept back wings, rather than the T-tail, that started the train of events.