RANGE REPLY SIGNAL
INTERROGATION SIGNAL
Distance Measuring Equipment (DME)
DME Identification
(Morse code approx. every 30 seconds)
•DME Cautions: Slant Range Distance
– Think of the ‘N’ or ‘0’ at the top of the dial as representing the “NOSE” of the aircraft rather than North.
Movable Card Indicator
–With MH set on movable card ADF • Tip of needle points to magnetic bearing TO NDB • Tail of needle points to magnetic bearing FROM NDB
• Combines VOR indicator with Heading Indicator
– bird’s eye view of your position – NO reverse sensing problems when tuned to
VOR
• Features
– instantaneous tracking awareness – position from desired radial
HSI Localizer
• Reverse Sensing when tuned to localizer unless front course is selected
– course selector must be set to the inbound front course
• for both front and back course instrument approaches
Bearing FROM the station
RMI Station Passage
• Identified when:
– needle drops to wingtip position – OR settles at 180°position
• Depending on altitude, from time of oscillation to station passage could be anywhere up to 3 minutes!
– Precipitation Static
• Static caused by rain, snow or clouds • needle fluctuations
Homing with ADF
HOMING results in a curved path to station if
there is wind
• Slant range - from aircraft to station
DME – BASIC OPERATION
DME TRANSMITTER (RECEIVER) MEASURES THE TIME IT TAKES FOR REPLY SIGNAL TO RETURN AND CONVERTS THIS TIME TO A DISTANCE IN NM
ADF Formula
– MH + RB = MB –Magnetic Heading (MH) –Relative Bearing (RB) –Magnetic Bearing (MB) –TO the station
–(add/subtract 180 for FROM)
MH + RB = MB (TO STATION)
Fixed Card ADF
– Bearing Needle always points to the relative bearing
– RELATIVE BEARING: How many degrees clockwise relative to the NOSE of the aircraft is the station located?
• Error greatest at sunrise and sunset- “twilight”
– Thunderstorm Effect
• needle points at lightning • - could navigate you to the nearest thunderstorm!
Distance Measuring Equipment (DME)
• Paired Frequencies (VOR and DME are locked together)
• How DME works
– pulsed signal pair – time to return
• Groundspeed feature is good directly to or from a station (but not 90 degrees to station)
arc • Change needle position relative to crosswind
influence
RMI, DME ARC
• Where should the bearing pointer be located relative to the wingtip reference to maintain the 16 DME range in a righthand arc with a right crosswind component? (fig. 107)
– Shoreline Effect
• Radio waves travel differently over water than over land.
– Night Effect
• signals bounced off ionosphere - needle fluctuations & interference from distant stations
FAA Fig. 105
Set aircraft heading on the compass rose of your E6B. Use your pencil as the needle and point TIP of pencil to “bearing TO station” or TAIL of pencil to “bearing FROM station. Match what you see on your “movable card” E6B to one of the indicators given as answer choice in FAA question. (see Gleim Instrument Knowledge Test Guide pg. 78
Precipitation Static
Shorelines Can Refract (Bend) The Signals When They Cross At Small A• Terrain Effect
• Mountains reflect radio waves, sometimes at an angle.
true ground speed, and ETA to that station. Careful Though...
Speed And ETA Are Only Accurate When Heading Directly Toward Or From The Station.
Distance Is Only Accurate Beyond Some Distance Away Due To “Slant Range”
DME
DME Arcs
• A method of not having to fly to the VORTAC and then proceed outbound to a procedure turn.
• Easiest with RMI • Series of tangent tracks around desired DME
– -Needle indicates MAGNETIC BEARING – (Must be manually set to heading)
–Radio Magnetic Indicator – -Needle indicates MAGNETIC BEARING
• (Automatically set to heading)
ADF Bearing Indicators
• Fixed Card Bearing Indicator • -Needle indicates RELATIVE BEARING • (Must be referenced to Heading
Indicator)
–Movable Card ADF Indicator
ADF Navigation
• Superimposing Heading Indicator to ADF works well with fixed card ADF
• Movable card ADF takes out a lot of guesswork
• Visualize using flight computer as heading indicator for FAA test questions
ADF Ground Facilities
• Non directional beacons • L/MF range
– 190 to 535 kHz
• No line of sight limitations • But: