•  Design maneuvering speed (V$_{A}$)—the maximum  speed at which the structural design’s limit load can  be imposed (either by gusts or full deflection of the  control surfaces) without causing structural damage.  It is important to consider weight when referencing  this speed. For example, V$_{A}$ may be 100 knots when  an airplane is heavily loaded, but only 90 knots when  the load is light.  •  Landing gear operating speed (V$_{LO}$)—the maximum  speed for extending or retracting the landing gear if  flying an aircraft with retractable landing gear.  •  Landing gear extended speed (V$_{LE}$)—the maximum  speed at which an aircraft can be safely flown with  the landing gear extended.  •  Best angle-of-climb speed (V$_{X}$)—the airspeed at  which an aircraft gains the greatest amount of altitude  in a given distance. It is used during a short-field  takeoff to clear an obstacle.  •  Best rate-of-climb speed (V$_{Y}$)—the airspeed that  provides the most altitude gain in a given period of time.  •  Single-engine best rate-of-climb (V$_{YSE}$)—the best  rate-of-climb or minimum rate-of-sink in a light  twin-engine aircraft with one engine inoperative. It is  marked on the ASI with a blue line. V$_{YSE}$ is commonly  referred to as “Blue Line.”  •  Minimum control speed (V$_{MC}$)—the minimum flight  speed at which a light, twin-engine aircraft can be  satisfactorily controlled when an engine suddenly  becomes inoperative and the remaining engine is at  takeoff power.  Instrument Check  Blockage of the Pitot-Static System  Blocked Pitot System  1.  The ASI would be zero.  2.  Dynamic pressure and static pressure are equal.  3. Because both dynamic and static air pressure are equal  at zero speed with  increased speed, dynamic pressure  Prior to takeoff, the ASI should read zero. However, if there  is a strong wind blowing directly into the pitot tube, the ASI  may read higher than zero. When beginning the takeoff,  make sure the airspeed is increasing at an appropriate rate.  Errors almost always indicate blockage of the pitot tube, the  static port(s), or both. Blockage may be caused by moisture  (including ice), dirt, or even insects. During preflight, make  sure the pitot tube cover is removed. Then, check the pitot and  static port openings. A blocked pitot tube affects the accuracy  of the ASI, but a blockage of the static port not only affects  the ASI, but also causes errors in the altimeter and VSI.  The pitot system can become blocked completely or only  partially if the pitot tube drain hole remains open. If the pitot  tube becomes blocked and its associated drain hole remains  clear, ram air is no longer able to enter the pitot system. Air  For example, take an aircraft and slow it down to zero knots  at a given altitude. If the st atic port (providing static pressure)  and the pitot tube (providing dynamic pressure) are both  unobstructed, the following claims can be made:  Because airspeed indications rely upon both static and  dynamic pressure together, the blockage of either of these  systems affects the ASI reading. Remember that the ASI has  a diaphragm in which dynamic air pressure is entered. Behind  this diaphragm is a reference pressure called static pressure  that comes from the static ports. The diaphragm pressurizes  against this static pressure and as a result changes the airspeed  indication via levers and indicators.  [Figure 8-10]  If both the pitot tube opening and the drain hole should  become clogged simultaneously, then the pressure in the pitot  tube is trapped. No change is noted on the airspeed indication  should the airspeed increase or decrease. If the static port  is unblocked and the aircraft should change altitude, then a  change is noted on the ASI. The change is not related to a  change in airspeed but a change in static pressure. The total  pressure in the pitot tube does not change due to the blockage;  however, the static pressure will change.  already in the system vents through the drain hole, and the  remaining pressure drops to ambient (outside) air pressure.  Under these circumstances, the ASI reading decreases to  zero because the ASI senses no difference between ram and  static air pressure. The ASI no longer operates since dynamic  pressure cannot enter the pitot tube opening. Static pressure  is able to equalize on both sides since the pitot drain hole  is still open. The apparent loss of airspeed is not usually  instantaneous but happens very quickly.  [Figure 8-9]  8-10  Figure 8-9.  A blocked pitot tube, but clear drain hole.  Static port  Drain hole  Pitot tube  Blockage 