lecture 8 : d istance m easuring e quipment ( dme )
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Lecture 8 : D istance M easuring E quipment ( DME ). Outlines. Introduction The uses of a DME DME Equipment How DME work? Advantages of DME Disadvantages of DME. Definition. DME is stand for D istance M easuring E quipment. - PowerPoint PPT PresentationTRANSCRIPT
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Lecture 8:Distance
Measuring Equipment (DME)
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Outlines
• Introduction
• The uses of a DME
• DME Equipment
• How DME work?
• Advantages of DME
• Disadvantages of DME
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Definition
• DME is stand for Distance Measuring Equipment.
• DME is a type of en-route navigation system for aircraft.
• DME often installed near VOR stations so as to provide combined bearing and distance.
• When DME is installed with the VOR, it is referred to as a VOR/DME.
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The uses of DME
• DME provides the physical distance from the aircraft to the ground DME transponder expressed in Nautical Miles (NM).
• DME also calculates ground speed and the time needed to reach the station if the aircraft is fitted with appropriate computer.
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DME System Components:
The DME system consists of three basic components which are:
• DME antenna on the aircraft body
• DME navigation display unit in aircraft cockpit
• DME transmitter/receiver in the ground
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DME INDICATOR IN THE COCKPIT
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DME Indicator
• DME enables aircraft to establish its range to the ground station: Distance in nautical miles, Ground speed in knots, Flying time to the station in minutes
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DME PRINCIPLE
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How DME works?
• DME provides distance (slant range) from the aircraft to the ground DME.
• DME operates on Ultra High Frequency (UHF) which is between 962 to 1213 MHz.
• DME works based on pulse techniques, where pulse means a single vibration of electric current.
• The aircraft’s antenna sends out paired pulses at specific spacing.
• The ground DME station receives the pulses and then responds with paired pulses at the same spacing but a different frequency.
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How DME works?
• The aircraft receiver measures the time taken to transmit and receive the signal which is transmitted into distance.
• Beside that, the distance formula is also used by the DME receiver to calculate the distance from DME station in Nautical Miles.
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Advantages of DME
• DME is extremely accurate: Provide continuous and accurate indication of the slant range distance.
• Aircraft Handling Capability: The transponder equipment should be capable of handling 100 to 200 aircrafts.
• Large coverage: DME facility provides coverage up to 200 NM.
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Disadvantages of DME
• As VOR the DME is also restricted to line-of-sight transmission. For example, the aircraft at altitude below 10’000 ft is unable to detect the DME signal.
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Disadvantages of DME
• Errors and abnormal indications:– Slant range
– Speed and time calculation
– Ground system saturation – 100 aircraft
– System error
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Exercise
• What is DME? Give two 2 uses of DME? (3 M)
• How DME works? (10 M)
• What the advantages of DME ( 2 M)
• What are the disadvantages of DME (1 M)
• What are 2 differences between VOR and DME? (2 M)
• An aircraft flying at altitude about 3 N.M (18’000ft). The ground distance is about 4 N.M. What is the distance (slant range) of the aircraft in N.M calculate by DME? (2 M)