Pre-stall Relative wind Relative wind Relative wind Initial stall Deep stall Pitch altitude Flightpath angle to the horizontal Angle of attack OC OC OC OC Figure 15-18.  Spoilers. Figure 15-17.  Deep stall progression. The primary purpose of speed brakes is to produce drag.  Speed brakes are found in many sizes, shapes, and locations  on different airplanes, but they all have the same purpose—to  assist in rapid deceleration. The speed brake consists of a  hydraulically-operated board that, when deployed, extends  into the airstream. Deploying speed brakes results in a rapid  decrease in airspeed. Typically, speed brakes can be deployed  at any time during flight in order to help control airspeed, but  they are most often used only when a rapid deceleration must  be accomplished to slow down to landing gear and flap speeds.  There is usually a certain amount of noise and buffeting  associated with the use of speed brakes, along with an obvious  penalty in fuel consumption. Procedures for the use of spoilers  and/or speed brakes in various situations are contained in the  FAA-approved AFM for the particular airplane. comply with an ATC request to go down and slow down at  the same time. Therefore, jet airplanes are  equipped with  drag devices, such as spoilers and speed brakes. The primary purpose of spoilers is to spoil lift. The most  common type of spoiler consists of one or more rectangular  plates that lie flush with the upper surface  of each wing.  They are installed approximately parallel to the lateral axis  of the airplane and are hinged along the leading edges.  When deployed, spoilers deflect up agains t the relative  wind, which interferes with the flow of  air about the  wing.  [Figure 15-18]  This both spoils lift and increases drag.  Spoilers are usually installed forward of the flaps but not in  front of the ailerons so as not to interfere with roll control. Jet airplanes have high kinetic energy during the landing  roll because of weight and speed. This energy is difficult to  dissipate because a jet airplane has low drag with the nose  wheel on the ground, and the engines continue to produce  forward thrust with the power levers at idle. While wheel  brakes normally can cope, there is an obvious need for  another speed retarding method. This need is satisfied by  the drag provided by reverse thrust. Deploying spoilers results in a substantial sink rate with  little decay in airspeed. Some airplanes exhibit a nose-up  pitch tendency when the spoilers are deployed, which the  pilot must anticipate. When spoilers are deployed on landing, most of the wing’s  lift is destroyed. This action transfers the airplane’s weight to  the landing gear so that the wheel brakes are more effective.  Another beneficial effect of deploying spoilers on landing is that  they create considerable drag, adding to the overall aerodynamic  braking. The real value of spoilers on landing, however, is  creating the best circumstances for using wheel brakes. A thrust reverser is a device fitted in the engine exhaust  system that effectively reverses the flow of the exhaust gases.  The flow does not reverse through 180°; however, the final  path of the exhaust gases is about 45° from straight ahead.  This, together with the losses in the reverse flow paths, results  in a net efficiency of about 50 percent. It produces even less  if the engine rpm is less than maximum in reverse. Normally, a jet engine has one of two types of thrust reversers:  a target reverser or a cascade reverser.  [Figure 15-19]  Target  15-15 Thrust Reversers