Distance Measuring Equipment (DME)

Question 1

DME Operating Principles

Answer 1

•Operates off of facilities with specific DME capabilities
•VOR/DME
•VORTAC
•TACAN
•LOC/DME
•ILS/DME

Question 2

How DME works

Answer 2

•Each DME channel consists of two frequencies
•Interrogation
•Response
•DME Uses Principle of Secondary RADAR
•Transponder = Transmit & Respond
•The time required for round trip of signal exchange measured by AIRBORNE UNIT (interrogator)
•Distance in Nautical Miles

Question 3

DME practical applications

Answer 3

•Reduces Pilot Workload
•Determine Position (Radial/DME)
•An Approach Aid
•VOR/DME Approach

Question 4

DME can be used with localizer

Answer 4

•As substitute for OUTER MARKER
•As back course FAF
•To establish other fixes on localizer course
•Basically – to identify a point in space, like a GPS waypoint

Question 5

DME accuracy

Answer 5

•Fairly Accurate
•1/2 mile or 3% of distance whichever is greater
•Reliable signals up to 199 nautical miles

Question 6

DME disadvantages

Answer 6

•Uses Slant Range
•Effected Line of Sight
•Certain aircraft maneuvers can block signal
•Service Volume - 100 aircraft maximum

Question 7

Slant range error

Answer 7

Aircraft is 18000 feet over VOR but DME reads 3 nm.

Question 8

DME common errors

Answer 8

•Failure to use it
•Careless tuning
•Failure to IDENT
•Not considering Slant Range when applicable
•Failure to recognize inaccurate DME readouts