Nav Equipment DME+VOR Flashcards
What does DME stand for?
Distance Measuring Equipment
What does a DME do?
Provides an Accurate slant range indicator that requires dedicated equipment both on the ground and in the aircraft
List the equipment required for VOR?
Distance indicator digital or analogue (inside the ac)
Interrogator(transmitter receiver) built in
Transponder(Receiver Responder)
What is the speed of a radio wave?
3million waves per second
How does a DME work?
1) Transponder gets interrogated by interrogator.
2) the transponder transmits to interrogator
3) Computer works out slant range from eclipsed time between Tx and Rx.
4) indicator show ranges (dial or linear display)
For DME why are two frequencies used?
To avoid aircraft interrogating each other.
What wave band does DME operate in?
UHF
How accurate is DME?
1nm
How many aircraft interrogators can a DME handle?
100 aircraft
The closer to the beacon the less accurate the readings become
(subject to slant error). True or False?
True
What do colocated VOR/DME stations provide?
(Slant) range and bearing
What are the uses of DME?
1) provides positive range for a/c flying same track and interrogating same DME
2) colocated with VOR (VOR/DME) provides range and bearing
3) co-located with precision approach for accurate range from touch down.
4) Enhances accuracy of holding pattern
5) Suitable computer n DME accurate area nav
6) Mil use for Air to Air refuelling
What does VOR stand for?
VHF Omni Directional Beacon
What does VOR do?
It’s a system that automatically and continuously provides an a/c with an accurate magnetic bearing from the beacon.
What is the principle of VOR?
Bearing by Phase Comparison
How does it work?
It exploits radio waves
What waveband does VOR operate in?
VHF
How are VORs identified?
By a 3 letter code or Speach.
VOR is line of sight and therefore depends on______\_________ for accuracy
Aircraft height
Name the two signals VOR operates.
1) Reference Signal
Variable Signal
How is the VOR reference signal transmitted?
Omni-directionally
How is a VOR variable signal transmitted?
By a circular array of aerials around the reference signal antenna, simulating a revolving antenna.
The two VOR signals are transmitted simultaneously but the simulated rotation causes a phase difference which varies with the change of bearing.
True or False?
True.
How many radials die a VOR transmit?
360
As in 360 degrees
The VOR transmits a useable signal above the beacon. True or False?
False.
What is the cone of silence/ confusion?
The area above the beacon in which it does not transmit a useable signal vertically upwards.
The period in which the a/c receives no signal increases with height. True or False?
True.
Which radio Modulation is used to transmit VOR radials?
FM
What is the different antenna system?
Circle/spherical aerials surrounded by
Large circle of horizontal reflectors (25) diameter
What does RMI stand for?
Radio Magnetic Indicator
How does the RMI work?
VHF Receiver operates using a total of 160 spot frequencies
How is the VOR displayed in the cockpit?
The magnetic bearing (QDM) is indicated by an arrow at one end of the arrow.
The radial (QDR) must be shown at the opposite end.
What does OBS stand for?
Omni-Bearing Selector (OBS)
What are the two forms of OBS?
1) Earlier Form
2) Later form
What information does the OBS Earlier form display?
1) Deflection left/ right of preselected QDM
2) shows whether the a/c is heading away or towards the beacon
What information does the later form of OBS show?
1) Shows same Information as Earlier form but for the purpose of ILS
2) includes fail flag when no signal is being received
OBS is a demand instrument, True or False?
True
The OBS tells the pilot his current heading. True or False?
True
The displacement scale on the OBS has dots. How many degrees does each dot represent?
2 degrees
When flying inbound to the beacon the magnetic course will be the reciprocal of the radial. True or False?
True
What is the accuracy of the OBS ?
+/- 1.25 degrees
What are the approximate ranges obtainable for reliable (protected) VOR Operation?
50nms at 1,000ft
90nms at 5,000ft
150nms at 15,000ft
200nms at 25,000ft
What are the VOR errors?
1) Site Errors
2) Propagation Errors
3) Equipment Errors
4) Interference Errors
What are Site Errors?
Poor beacon siting can produce reflected signals from ground/buildings that can cause bearing errors
What are propagation errors?
Caused by uneven propagation over long distances or irregular terrain.
What is equipment error?
Caused by incorrect tuning or calibration
What is interference error?
The narrow operating band limits the number of channels available and high flying aircraft run the risk of receiving signals more than one VOR on the same frequency.
How far are VORs on the same frequency separated by?
500nm
List the 7 uses for VOR.
1) Homing to a station
2) Maintaining a Track along an airway centre line
3) Obtaining a position line
4) Flying a holding pattern
5) Flying an IAP with a suitable position beacon
6) Obtaining a fix with 2 or more VORs
7) -Broadcast ATIS/ other Information
What frequency does the interrogator transmit on?
1030MHz
What frequency does the transponder transmit on?
1090MHz
What distance inside the range of the DME can it not be used?
15nm