7. DME And VOR Flashcards
What is a DME?
Distance Measuring Equipment
Accurate, slant range indicator that requires dedicated equipment both on the ground and in
the aircraft.
Operates in UHF waveband
Accurate to within 1nm
How does DME work?
DME replies with the same train of irregular pulses it
receives but on a different frequency.
Two frequencies are used to avoid aircraft
interrogating each other.
Interrogator recognizes own original pulse train and
calculates time taken from transmission to reception.
The pulse train varies unpredictably to distinguish it
from one transmitted from another aircraft.
Increased working range due to two transmitters.
Errors of DME?
Subject to slant error - the closer to the beacon, the less accurate the readings become.
Uses of DME?
- Can accept up to 100 aircraft interrogations simultaneously.
- Co-located VOR/DME stations provide range and bearing.
- Provides positive ranges for aircraft flying same track and interrogating same DME ∴ ATC separation.
- Co-location with precision approach aid ∴ accurate range from touchdown (ILS)
- Enhances the accuracy of holding patterns.
- Suitable computer + DME ∴ accurate area navigation.
- Military use for air to air refueling
What is VOR?
VHF Omni-directional Radio Range
Radiates Radials
Identified by either a 3 letter Morse code, or speech.
“DOH”
Operates in VHF waveband between: 108-117.95 MHz.
VOR Errors (4)
P I S E
- Propagation Errors
Caused by uneven propagation over long
distance or irregular terrain.
- Interference Errors
The narrow operating bands limits the number
of channels available, and high flying aircraft run
the risk of receiving signals from more than one
VOR on the same frequency when at or near the
protected range of a beacon.
VOR’s on the same frequency are therefore
spaced 500nms apart
- Site Errors
Poor beacon siting can produce reflected signals
from high ground and buildings that can cause
bearing errors.
- Equipment Errors
Caused by incorrect tuning or calibration.
Uses of VOR? (7)
- Homing to a station.
- Maintaining track along an airway centreline.
- Obtaining a position line.
- Flying a holding pattern.
- Flying instrument approaches with a suitable positioned beacon.
- Obtaining a fix with two or more VORs’.
- Broadcast ATIS (Local Aerodrome information) and other information.
How does a VOR work?
VOR operates using two signals:
Reference Signal is transmitted Omni-directionally.
Variable Signal is transmitted by a circular array of aerials around the Reference Signal antenna,
simulating a revolving antenna
System that automatically and continuously provides an aircraft with an accurate magnetic bearing from a beacon.
What information does a DME provide to a pilot?
slant range distance from the station
A system that automatically and continuously provides an aircraft with an accurate magnetic bearing
from a beacon, operating in the VHF waveband, is called a?
VOR
What is the Cone of Confusion?
The VOR beacon does not transmit a usable signal vertically upwards.
This leads to a Cone of Confusion/Cone of Silence. The period during which the aircraft receives no signal
increases with height.
What are the components of a VOR & how is it situated?
Different antenna system: Circle of spherical
aerials, surrounded by larger circle of horizontal reflectors (25m diameter). Radial information transmitted
by FM. Fed to antenna aerial in such a way that phase angle changes radially through 360°. Permits
installation in difficult terrain but is expensive to equip and install. Radials always extend outwards from
the VOR.
What is an RMI?
The VHF receiver operates using a total of 160 spot frequencies. VOR is displayed in
the cockpit via: The magnetic bearing of the beacon (QDM) is indicated by an arrow at one end of the VOR
pointer. The radial (QDR) must be shown at the opposite end.
The VOR shares part of its freq. spectrum with the?
Localiser (LLZ) of the ILS
A VOR produces radials/tracks at 2° spacing which are aligned in relation to magnetic north at the VOR
location?
False
