1.
    The fuel system is designed to provide an uninterrupted flow of clean fuel from the fuel tanks to the engine. The fuel must be available to the engine under all conditions of engine power, altitude, attitude, and during all approved flight maneuvers. Two common classifications apply to fuel systems in small airplanes gravity-feed and fuel-pump systems.
    The gravity-feed system utilizes the force of gravity to transfer the fuel from the tanks to the engine，for example, on high-wing airplanes where the fuel tanks are installed in the wings. This places the fuel tanks above the carburetor, and the fuel is gravity fed through the system and into the carburetor. If the design of the airplane is such that gravity cannot be used to transfer fuel, fuel pumps are installed，for example, on low-wing airplanes where the fuel tanks in the wings are located below the carburetor.
  燃油系统是设计用来提供持续的从油箱到发动机的洁净燃油流量。燃油在所有发动机功率，高度，姿态和所有核准的飞行机动条件下必须能够供给发动机。小飞机上使用了两个常规类别的燃油系统-重力馈送系统和燃油泵系统。
  重力馈送系统使用重力来把燃油从邮箱输送到发动机，例如，在上翼飞机上，油箱是安装在机翼里的。油箱被置于汽化器之上，燃油由于重力经过系统送到汽化器。如果飞机的设计不能用重力输送燃油，就要安装油泵，例如，在下翼飞机上机翼中的邮箱处于汽化器下方。
2.
FUEL PRIMER
Both gravity fed and pump systems may incorporate a fuel primer into the system. The primer is used to draw fuel from the tanks to vaporize it directly into the cylinders prior to starting the engine. This is particularly helpful during cold weather, when engines are hard to start because there is not enough heat available to vaporize the fuel in the carburetor. It is important to lock the primer in place when it is not in use. If the knob is free to move, it may vibrate out during flight and can cause an excessively rich mixture.
起动注油器
重力馈送和油泵系统也可以结合气动注油器。启动注油器用于气动发动机之前从油箱中抽油
直接气化送入气缸。在冷天气特别有用，那时发动机会很难气动，因为没有足够的热量来气化汽化器中的燃油。气动注油器在不使用时锁定位置很重要。如果旋钮可以自由活动，飞行中它会被振动出来，引起过分富油。
3.
  Wind shear is a sudden, drastic change in wind speed and/or direction over a very small area. Wind shear can subject an aircraft to violent updrafts and downdrafts as well as abrupt changes to the horizontal movement of the aircraft. While wind shear can occur at any altitude, low-level wind shear is especially hazardous due to the proximity of an aircraft to the ground. Directional wind changes of 180° and speed changes of 50 knots or more are associated with low-level wind shear. Low-level wind shear is commonly associated with passing frontal systems, thunderstorms, and temperature inversions with strong upper level winds (greater than 25 knots).
  Wind shear is dangerous to an aircraft for several reasons. The rapid changes in wind direction and velocity change the wind’s relation to the aircraft disrupting the normal flight at
titude and performance of the aircraft. During a wind shear situation, the effects can be subtle or very dramatic depending on wind speed and direction of change. For example, a tailwind that quickly changes to a headwind will cause an increase in airspeed and performance. Conversely, when a headwind changes to a tailwind, the airspeed will rapidly decrease and there will be a corresponding decrease in performance. In either case, a pilot must be prepared to react immediately to the changes to maintain control of the aircraft.
  风切变是指在一个非常小的区域内风速和/或方向的突然的，激烈的变化。风切变会使飞机受突然的上升气流和下降气流影响，以及飞机水平运动的突然改变。虽然风切变可以发生在任何高度，由于飞机接近地面，低空的风切变是特别的危险。风的方向180 度变化和速度的50节变化或者更多都和低空风切变有关。低空风切变通常会伴随偶然的锋面系统，雷暴，强烈的高空风(大于25 节)温度翻转而出现。
  风切变对飞机的危险有多个原因。风向和速度的快速变化改变了飞机的相对风，破坏了飞机的正常飞行高度和性能。在风切变状态下，影响可能很小，也可能很明显，这都看风速和风向的变化。例如，顺风很快的变为逆风将很快的导致空速和性能的增加。相反地，当迎风
变为顺风时，空速会快速降低，性能也会相应的降低。任一情况下，飞行员必须准备好对维持飞机控制的变化做出立即反应。
4.
DENSITY ALTITUDE
The more appropriate term for correlating aerodynamic performance in the nonstandard atmosphere is density altitude— the altitude in the standard atmosphere corresponding to a particular value of air density. Density altitude is pressure altitude corrected for nonstandard temperature. As the density of the air increases (lower density altitude), airplane performance increases and conversely as air density decreases (higher density altitude), airplane performance decreases. A decrease in air density means a high density altitude; and an increase in air density means a lower density altitude.
Density altitude is used in calculating airplane performance. Under standard atmospheric condition, air at each level in the atmosphere has a specific density, and under standard coreact to翻译
nditions, pressure altitude and density altitude identify the same level. Density altitude, then, is the vertical distance above sea level in the standard atmosphere at which a given density is to be found.
和非标准大气条件下的空气动力学性能有关的更合适的术语是密度高度- 对应于特定空气密度时的标准大气条件下的高度。密度高度是经非标准温度修正后的压力高度。当空气的密度增加(较低的密度高度)时，飞机性能增加，相反地，随着空气密度降低(较高的密度高度)时，空气性能降低。空气密度的下降意味着高密度高度；空气密度增加意味着较低的密度高度。密度高度用于计算性能。在标准大气条件下，大气中每个高度上的空气都有特定的密度，且在标准条件下，压力高度和密度高度表示的高度相同。因而，密度高度是标准大气条件下给定密度位置在海平面上的垂直距离。
5.
RUNWAY MARKINGS
Runway markings vary depending on the type of operations conducted at the airport. Figur
e 12-3 shows a runway that is approved as a precision instrument approach runway and also shows some other common runway markings. A basic VFR runway may only have centerline markings and runway numbers.

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