(1) the navigation system compute and display the airplane’s position and movement over the earth’s surface. The navigation systems include the following main subsystems:
.  ADF automatic direction finder — ADF system provide a display of the relative bearing to a selected ground transmitter.

.  VOR/ILS(very high frequency omnirange/instrument landing system)— this system provide displays of relative and magnetic bearing to a selected

VOR station and deviation from a preselected course. When truned to an ILS frequency, the system provides a display of the lateral and vertical deviation from the optimum landing path.

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DOM(distance measuring equipment) —DME system measures the slant range distance to the selected DME facility.

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ATC (air traffic control)— ATC system transmits airplane identification and altitude data to a ground facility.

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ADS (air data system)— ADS system measures pitot and static pressure and total air temperature and computes various air data parameters.

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IRS(inertial reference system)— this system provides outputs of key navigation parameters such as heading, attitude, and airplane present position.

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EFIS(electronic flight instrument system )— this system providesdisplays of information from various airplane systems.

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WXR(weather radar) —this system provides a display of the weather conditions forward of the airplane, and can also provide a map display.

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LRRA(low range radio altimeter)— this system measures the absolute height of the airplane above the earth’s surface.

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GPWS(ground proximity warning system)— this system uses inputs from other systems to navigatee the airplane and provide optimization of the flight plan.

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FMCS(flight management computer system)— this system provides the pitot with aural and visual warning of an unsafe flight path relative to the earth’s surface.

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MKR BCN(marker beacon ) —this system provides an indication when the airpnale is passing over a specific position.

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TCAS(traffic alert and collision avoidance system)— this system provides the pitots with warnings and advisories of unsafe flight conditions with regard to other airplanes operating in the area.

. 导航系统计算并显示飞机的位置及其在地球表面的移动。导航系统包括下列子系统：

. 自动定向机——此系统提供一个相对一个选定的地面发射台的相对方位角显示。