Nav 2 Exam Flashcards
Definition of DME
Accurate slant range indicator that requires dedicated equipment both on the ground and in the aircraft.
What frequency does DME work in and what equipment does it need
UHF
Transponder (receiver responder)
Interrogator (transmitter receiver)
Distance indicator (digital or analogue)
How many frequencies are used for DME and why?
2
To avoid a/c interrogating each other
Why does the pulse pair of DME vary?
To give it’s own unique code and distinguish it from other a/c
How accurate is DME
To within 1NM
How many a/c interrogations can DME accept?
Up to 100
What is slant error
The closer to the beacon you are the less accurate the reading is
What equipment does an a/c need to be fitted with to use DME
Interrogator
Distance indicator
Why do we use DME
Enhances accuracy of holding patterns
Military use for air to air refuelling
Can be collocated with VOR and precision approach aids
What do VORs do
Give bearings by phase comparison
How do VORs identify themselves
3 letter morse code or speech
VOR use line of sight true or false
True
What does VOR operating range depend on?
A/c height
What are the 2 signals VOR uses and how are they transmitted
Reference signal transmitted omni-directionally
Variable signal transmitted by a circular range of aerials around reference signal antenna simulating a revolving antenna
Are the 2 VOR signals transmitted simultaneously?
Yes but simulated rotation causes a phase difference which varies with change of bearing
Where does a VOR not transmit a useable signal?
Vertically
This is called cone of silence or cone of confusion
Increases with height
What extends outwards from VOR
Radials
Benefit of VOR and a downside
Can Install in difficult terrain
Expensive to equip and install
What is QDM
Magnetic heading to the beacon/station (aka homing)
What is QDR
Magnetic bearing from the beacon/station
I.e radial
What does OBS stand for and what does it do?
Omni bearing selector
Instrument on A/c which shows them general heading to or from beacon and VOR info.
Name 4 VOR errors
Site error
Propagation error
Equipment error
Interference error
What are the approx ranges obtainable for reliable VOR ops
50nm at 1000ft
90nm at 5000ft
150nm at 15000ft
200nm at 25000ft
What is the accuracy of VOR
+/- 1.25 degrees
How far apart are VORs spaced
50-100nm to ensure local coverage
What are VORs used for
Hoping to a station
Flying holding pattern
Maintaining track along airway centreline
Obtaining a position line
What is interference error in VOR
Narrow operating bands limits number of channels.
Huh flying a/c may receive signals from more than one VOR on same frequency
To rectify VOR on same frequency must be 500nm apart
What is RDF
Radio direction finding
The measurement of the direction from which a received signal was transmitted
What is a radio bearing
The angle between the apparent direction of a definite source of emission of radio waves and a reference direction as determined at DF station
What is a true radio bearing
Radio bearing who’s reference direction is true north
What is a magnetic radio bearing
A radio bearing for which the reference direction is magnetic north
What does DRDF stand for
Digital radio direction finding
what are the DF accuracy tolerance classes?
A +/- 2 degrees
B +/- 5 degrees
C +/- 10 degrees
D worse than class C
What are the uses of DF for ATCOs
Can assist a pilot who is lost
What is QTE
Time bearing of a/c in relation to DF station or other specified point
What is triangulation
Pilots can establish their approx position by obtaining 2 or more bearings for separate DF stations and plotting the point the bearings intercept
What is homing
Using the DF equipment and radio bearing to proceed continuously towards the station.
When can you refuse to give DF bearing headings or position
Conditions unsatisfactory
Bearings don’t fall in stations calibration limits
Doing so would monopolise the frequency
What is an ADF? What frequency does it use
Automatic direction finder.
Operates 300khz to 3mhz
Fitted in an a/c
What is an NDB
Omni directional transmitter that operates MF 190-1750khz
Average radius of cover between 10&500nm
When are high powered NDBs used
For long range navigation
When are low powered NDBs used
Airfield approach aids - locator beacons
What is RMI
Radio magnetic indicator - arrow superimposed onto compass rose used to read QD
Can have more than 1 arrow to show multiple beacons
What is RBI
Relative bearing indicator
Shows relative bearing in relation to a/c heading
To obtain bearing to NDB - a/c heading must be added to RBI reading
What are the 7 NDB errors
1 static interference 2 station interference 3 mountain effect 4 night effect 5 coastal refraction 6 quadrantal error 7 system malfunction
What is NDB static interference
Heavy precipitation and TS cause static. ADF needle points into TS
What is NDB mountain effect
LF andMF surface waves reflected by high ground - overcome by flying high
What is NDB coastal refraction
Radio waves travel faster over sea. Any angle except 90 degrees refracted
What is quadrantal error (NDB)
A/c frame reflects, refracts and re radiates incoming radio waves.
When are maximum and minimum NDB ranges experienced
Maximum from high power NDB at night over sea
Minimum from low powered NDB at airfields
Advantages of NDB
Reception not limited to line of sight - follows curvature of earth
Max range dependent on power of NDB
NDB disadvantages
Subject to atmospheric interference, coastal and night refraction which affects bearing accuracy
Is not as accurate at VOR
ILS definition
A precision runway approach that provides accurate guidance both in azimuth and elevation
What are runways served by an ILS called?
Precision approach instrument runway
ILS uses and benefits
Pilot interpreted aid
Designed for low cloud base or poor vis
Assist in achieving orderly flow of landing traffic
Operate continuously without assistance from ATC
What is a localiser transmitter
Defines extended centreline
Indicates deviation from optimum lateral approach path
Upwind end of rwy approx 300m from threshold
What is a glide path transmitter
Defines safe descent slope (usually 3 degrees)
Situated 300m from landing threshold and offset between 100&200m from centreline
What are the marker beacons and where are they located
Installed on approach to define ranges from the threshold
Outer 3-6nm from threshold
Middle 900-1200m from threshold
Inner 300-450m from threshold
What is a DME transponder and what does it do
Provides range info - used instead of marker beacons
Frequently paired with localiser - DME autotunes when ILS selected
Accurate only with localiser Coverage up to 25000ft
Range 0 degrees at threshold
What does a localiser do?
Transmits a signal in the 108-112 MHz VHF band
Radiates 2 lobes which overlap by 5 degrees
Flight receives signals of equal intensity from both lobes when on centreline
Coverage goes out to 35 degrees either side of centreline out to 17nm and thereafter at 10 degrees
ILS localisers provide coverage from centre of localiser antenna to distances of…
25nm within 10 degrees of course line
17nm within 35 degrees (25 degrees plus the other 10 degrees)
What does the glide path do?
Operates 329.3-335 MHz UHF band
Radiates 2 lobes which overlap by 1 degree out to a max of 10nm
Overlapping area subtends an angle of 3 degrees to give continuous descending approach to touch down point.
When on correct descent path will receive signals of equal intensity
What is the glide path aerial also known as
ILS reference point
What is the glide path protected range
Out to 10nm
Horizontally 8 degrees either side of centreline
Vertically 0.45 x GP below surface and 1.75 x GP above
What do glidepath aerial locations and approach angles depend on
A/c likely to use
Terrain
Obstacles within approach or missed approach
Local met conditions
Rwy length
ILS reference datum
Affects location of the glide path aerial
50ft across threshold
Rate of height loss depends on approach angle
2.5 degrees = 250ft per nm
3 degrees = 300ft per nm
3.5 degrees = 350ft per nm
Why are localiser and glidepath transmissions frequency paired
Reduces cockpit workload
Guards against mismatching
Only localiser frequency needs to be published
What does ILS automatic equipment monitor?
Radiation fields of
Localiser
Glidepath
Markers
If an ILS is under maintenance or radiating due test purposes how would pilot know
Identifier removed or replaced by continuous tone
How does a/c identify an ILS
3 letter morse code ID on localiser carrier wave
What happens if ILS power drops below an acceptable level
Automatically ceases to transmit
ATC and pilot warned
How is ILS displayed in cockpit
HSI (horizontal situation indicator) and OBS (omni directional bearing selector)
Each dot indicates out by 0.5 degrees horizontal 0.15 degrees vertical
When will needle remain fixed on ILS cockpit display
When the RX is switched off
No signal received
A/c is on centreline of both loc and GP beams
When can pilot use auto land
A/c equipment suitable
TX protected from external interference
ILS sensitive area
What are the ILS categories and what are they based on
Cat 1 Lower than cat 1 Cat 2 Lower than standard cat 2 Cat 3 (a,b,c)
Based on rwy lights and protection from infringements
What is ILS cat 1
DH not lower than 200ft
Vis not less than 800m OR RVR not less than 550m
What is ILS lower than standard cat 1
DH 200ft
RVR lower than cat 1 (550m) but not lower than 400m
What is ILS cat 2
DH lower than 200ft
RVR not less that 350m
What is ILS other than standard cat 2
ILS or MLS
Some or all elements of cat 2 light system not available
DH below 200ft but not lower than 100ft
RVR not less than 350m
What is ILS Cat 3 A
DH lower than 100ft
Or
No decision height and RVR not less than 200m
What is ILS cat 3 B
DH Lower than 50ft
Or
No DH and RVR less than 200m but not less than 75m
What is ILS cat 3 C
Blind landings
No DH no RVR limits
