Performance Speeds  For instance, a pilot is downwind for runway 18, and the  tower asks if runway 27 could be accepted. There is a light  rain and the winds are out of the east at ten knots. The pilot  accepts because he or she is approaching the extended  centerline of runway 27. The turn is tight and the pilot must  descend (dive) to get to runway 27. After becoming aligned  with the runway and at 50 feet AGL, the pilot is already 1,000  feet down the 3,500 feet runway. The airspeed is still high  by about ten percent (should be at 70 knots and is at about  80 knots). The wind of ten knots is blowing from behind.  First, the airspeed being high by about ten percent (80 knots  versus 70 knots), as presented in the performance chapter,  results in a 20 percent increase in the landing distance.  In performance planning, the pilot determined that at 70  knots the distance would be 1,600 feet. However, now it  is increased by 20 percent and the required distance is now  1,920 feet.  True airspeed (TAS)—the speed of the aircraft in relation to  the air mass in which it is flying.  Indicated airspeed (IAS)—the speed of the aircraft as  observed on the ASI. It is the airspeed without correction for  indicator, position (or installation), or compressibility errors.  Calibrated airspeed (CAS)—the ASI reading corrected for  position (or installation) and instrument errors. (CAS is  equal to TAS at sea level in standard atmosphere.) The color  coding for various design speeds marked on ASIs may be  IAS or CAS.  The newly revised landing distance of 1,920 feet is also  affected by the wind. In looking at  Figure 11-19 , the affect  of the wind is an additional 20 percent for every ten miles  per hour (mph) in wind. This is computed not on the original  estimate but on the estimate based upon the increased  airspeed. Now the landing distance is increased by another  320 feet for a total requirement of 2,240 feet to land the  airplane after reaching 50 feet AGL.  That is the original estimate of 1,600 under planned conditions  plus the additional 640 feet for excess speed and the tailwind.  Given the pilot overshot the threshhold by 1,000 feet, the  total length required is 3,240 on a 3,500 foot runway; 260  feet to spare. But this is in a perfect environment. Most pilots  become fearful as the end of the runway is facing them just  ahead. A typical pilot reaction is to brake—and brake hard.  Because the aircraft does not have antilock braking features  like a car, the brakes lock, and the aircraft hydroplanes on  the wet surface of the runway until decreasing to a speed of  about 54 knots (the square root of the tire pressure ( √ 36)  ×  9). Braking is ineffective when hydroplaning.  The 260 feet that a pilot might feel is left over has long since  evaporated as the aircraft hydroplaned the first 300–500 feet  when the brakes locked. This is an example of a true story,  but one which only changes from year to year because of new  participants and aircraft with different N-numbers.  In this example, the pilot actually made many bad decisions.  Bad decisions, when combined, have a synergy greater  than the individual errors. Therefore, the corrective  actions become larger and larger until correction is almost  impossible. Aeronautical decision-making is discussed more  fully in Chapter 2, Aeronautical Decision-Making (ADM).  V$_{A}$—the calibrated design maneuvering airspeed. This is  the maximum speed at which the limit load can be imposed  (either by gusts or full deflection of the control surfaces)  without causing structural damage. Operating at or below  V$_{FE}$—the highest speed permissible with the wing flaps in a  prescribed extended position. This is because of the air loads  imposed on the structure of the flaps.  V$_{LO}$—the maximum speed at which the landing gear can  be safely extended or retracted. This is a problem involving  the air loads imposed on the operating mechanism during  extension or retraction of the gear.  V$_{LE}$—the maximum speed at which the aircraft can be safely  flown with the landing gear extended. This is a problem  involving stability and controllability.  V$_{X}$—the speed at which the aircraft obtains the highest  altitude in a given horizontal distance. This best AOC speed  normally increases slightly with altitude.  V$_{Y}$—the speed at which the aircraft obtains the maximum  increase in altitude per unit of time. This best ROC speed  normally decreases slightly with altitude.  V$_{S1}$—the calibrated power-off stalling speed or the minimum  steady flight speed at which the aircraft is controllable in a  specified configuration.  V$_{S0}$—the calibrated power-off stalling speed or the minimum  steady flight speed at which the aircraft is controllable in the  landing configuration.  Equivalent airspeed (EAS)—the ASI reading corrected  for position (or installation), for instrument error, and for  adiabatic compressible flow for the particular altitude. (EAS  is equal to CAS at sea level in standard atmosphere.)  11-18 