仪表飞行员地面课程Lesson 4.ppt

DME (cont.) Navaids which provide distance information as well as azimuth VOR/DME VORTACs TACANs ILS/DME DME (cont.) DME Operation Airborne equipment sends an electronic interrogation to the ground station, which gives an electronic response. By timing the interval between interrogation and response, the airborne DME calculates how far the signals are traveling. Ground based station has a finite number of DME interrogations. Turn off DME when not needed (ie. On ground). DME cautions Slant Range Error The difference between the actual horizontal distance and the slant range DME measures the distance between the aircraft and the ground station Slant range error is considered negligible when the airplane’s altitude in thousands of feet is less the distance in nautical miles (10 miles out, 5000 feet) DME Slant Range Error DME (cont.) DME Identification DME has its own identifier Morse code is the same as that for the associated VOR, but with higher pitch DME identification is transmitted about every 30 seconds DME Accuracy Limited to line of sight Reliable signals at distances of 199 NM with accuracy of better then ? mile or 3% distance whichever is greater DME (cont.) Typical DME receivers/antenna Horizontal Situation Indicator (HSI) Combines information from DG and VOR into one display Improves orientation by eliminating “reverse sensing” and directly showing intercept angles Increases efficiency of instrument scan Usually is slaved to remote flux valve to minimize precession Gyro can be vacuum or electrically driven HSI (cont.) HSI Indicator components Typical HSI indicators HSIorientation HSIorientation * Sierra Academy of Aeronautics IR Ground Lesson 4 VOR/DME Current Navigational Equipment in Use VOR (VHF Omni-directional Range) Very High Frequency Omni-Directional Range (VOR) Currently the primary navigational aid used by civil aircraft in the National Airspace System 2 types Basic VOR provides only course guidance and basic orientation VOR DME