of the airplane as the stall develops and the loss of tail  effectiveness at the stall. The handling qualities down to the  stall are much the same as the straight wing airplane except  that the high, T-tail remains clear of the wing wake and  provides little or no warning in the form of a pre-stall buffet.  Also, the tail is fully effective during the speed reduction  towards the stall, and remains effective even after the wing  has begun to stall. This enables the pilot to drive the wing  into a deeper stall at a much greater AOA. In an unmodified swept wing, the tips first stall, results in a  shift of the center of lift of the wing in a forward direction  relative to the center of gravity of the airplane, causing a  tendency for the nose to pitch up. A disadvantage of a tip first  stall is that it can involve the ailerons and erode roll control.  To satisfy certification criteria, airplane manufacturers may  have to tailor the airfoil characteristics of a wing as it proceeds  from the root to the tip so that a pilot can still maintain wings  level flight with normal use of the controls. Still, more  aileron will be required near stall to correct roll excursion  than in normal flight, as the effectiveness of the ailerons will  be reduced and feel mushy. This change in feel can be an  important recognition cue that the airplane may be stalled. As previously stated, when flying at a speed near VMD, an  increase in AOA causes drag to increase faster than lift and  the airplane begins to sink. It is essential to understand that  this increasing sinking tendency, at a constant pitch attitude,  results in a rapid increase in AOA as the flightpath becomes  deflected downwards.  [Figure 15-17]  Furthermore, once  the stall has developed and a large amount of lift has been  lost, the airplane will begin to sink rapidly and this will be  accompanied by a corresponding rapid increase in AOA. This  is the beginning of what is termed a deep stall. At the stall, two distinct things happen. After the stall, the  sweptwing T-tail airplane tends to pitch up rather than down,  and the T-tail can become immersed in the wing wake,  which is low energy turbulent air. This greatly reduces tail  effectiveness and the airplane’s ability to counter the nose- up pitch. Also, if the AOA increases further, the disturbed,  relatively slow air behind the wing may sweep across the tail  at such a large angle that the tail itself stalls. If this occurs,  the pilot loses all pitch control and will be unable to lower  the nose. The pitch up just after the stall is worsened by large  reduction in lift and a large increase in drag, which causes a  rapidly increasing descent path, thus compounding the rate  of increase of the wing’s AOA.  [Figure 15-15] A slight pitch up tendency after the stall is a characteristic of  a swept or tapered wings. With these types of wings, there  is a tendency for the wing to develop a spanwise airflow  towards the wingtip when the wing is at high angles of attack.  This leads to a tendency for separation of airflow, and the  subsequent stall, to occur at the wingtips first.  [Figure 15-16] As an airplane enters a deep stall, increasing drag reduces  forward speed to well below normal stall speed. The sink  rate may increase to many thousands of feet per minute. It  must be emphasized that this situation can occur without an  excessively nose-high pitch attitude. On some airplanes, it  can occur at an apparently normal pitch attitude, and it is this  quality that can mislead the pilot because it appears similar to  the beginning of a normal stall recovery. It can also occur at a  negative pitch attitude, that is, with the nose pointing towards  the ground. In such situations, it seems counterintuitive to  apply the correct recovery action, which is to push forward  on the pitch control to reduce the AOA, as this action will  also cause the nose to point even further towards the ground. But, that is the right thing to do. Deep stalls may be unrecoverable. Fortunately, they are easily  avoided as long as published limitations are observed. On those  airplanes susceptible to deep stalls (not all swept or tapered  wing airplanes are), sophisticated stall warning systems such  as stick shakers are standard equipment. A stick pusher, as its  name implies, acts to automatically reduce the airplane’s AOA  before the airplane reaches a dangerous stall condition, or it  may aid in recovering the airplane from a stall if an airplane’s  natural aerodynamic characteristics do so weakly. Pilots undergoing training in jet airplanes are taught to  recover at the first sign of an impending stall instead of going  beyond those initial cues and into a full stall. Normally, this  15-13 Figure 15-15.  Stall progression—sweptwing airplane. Stalled Prestall