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A course deviation indicator (CDI) is an avionics instrument used in aircraft navigation to determine an aircraft's lateral position in relation to a course. If the location of the aircraft is to the left of course, the needle deflects to the right, and vice versa. ==Use== The indicator shows the direction to steer to correct for course deviations. Correction is made until the vertical needle centers, meaning the aircraft has intercepted the given courseline. The pilot then steers to stay on that line. Only the receiver's current ''position'' determines the reading: the aircraft's heading, orientation, and track are not indicated. The deflection of the needle is proportional to the course deviation, but sensitivity and deflection vary depending on the system being used: * When used with a GPS it shows actual distance left or right of the programmed courseline. Sensitivity is usually programmable or automatically switched, but deviation at full scale is typical for en route operations. Approach and terminal operations have a higher sensitivity up to frequently at full scale. * When used with a VOR or VORTAC the courseline is selected by turning an "omni bearing selector" or "OBS" knob usually located in the lower left of the indicator. It then shows the number of degrees deviation between the aircraft's current position and the "radial" line emanating from the signal source at the given bearing. This can be used to find and follow the desired radial. Deflection is 10° deviation at full scale, with each dot on the CDI representing 2°. (See Using a VOR for usage during flight.) * When used for instrument approaches using a LDA or ILS the OBS knob has no function because the courseline is usually the runway heading, and is determined by the ground transmitter. A CDI might incorporate a horizontal needle to provide vertical guidance when used with a precision ILS approach where the glideslope is broadcast by another transmitter located on the ground. A CDI is not used with an automatic direction finder (ADF), which receives information from a normal AM radio station or an NDB. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「course deviation indicator」の詳細全文を読む スポンサード リンク
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