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Flashcards in Nav 02 Deck (143)
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1

What errors is a VOR subject to?

Site errors

Poor sighting

Propogation errors

Uneven propogation caused by terrain over long distances

Equipment errors

Incorrect tuning or calibration

Interference errors

Signal interference from other radio sources.

2

What is a VOR?

A VHF omni-directional radio range. Provides aircraft with a radial from the VOR letting you know where you are in relation to it. It works by transmitting two signals, a reference signal (which is the same in every direction) and a directional signal which varies dependent on the direction you are from the VOR (due to a set of antennas around the VOR which have varying signals programmed), the phase difference between these signals gives you your radial from the VOR. Often co-located with a DME.

Information is displayed on the VOR receiver in the cockpit which indicates the magnetic course to the VOR selected radial or your radial.

Transmits a unique 3 letter identifier via morse code

Signal is FM and VHF.

3

What is a DME?

Distance measuring equipment. A transponder on the ground that is interrogated by the aircraft transponder before being transmitted back. The time the signal takes to return is used to calculate the slant range of the aircraft from the DME. Gives range in NM. Can be interrogated by up to 100 aircraft at once. Operates UHF. Slant range error can make the reading inaccurate the closer the aircraft is and the higher it is.

Information is displayed on the DME receiver in the cockpit.

4

What is the accuracy of a VOR?

• Accuracy is plus or minus 1.25º

-50nms at 1,000ft

-90nms at 5,000ft

-150nm at 15,000ft

-200nms at 25,000ft

Ie LOS means the higher you are the further away you can pick up the signal.

• Spaced between 50nm and 100nms apart to ensure low level coverage.

  • Also has the cone of silence as VOR will not work for aircraft directly above it.

5

What is the accuracy of an DME?

• Accurate to within 1nm

• Can accept up to 100 aircraft interrogations simultaneously

• Subject to slant error - the closer to the beacon, the less accurate the readings become

6

How are DME's used?

• 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 eg ILS

• Enhances the accuracy of holding patterns

• Suitable computer + DME accurate area navigation

• Military use for air to air refueling

7

How is a VOR radial displayed in the cockpit?

Radio Mangentic Indicator (RMI)

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.

Omni -bearing Selector (OBS)

Shows the QDM deflection from the VOR, ie tells you which way you need to reposition the aircraft to acquire the desired track relative to the VOR but doesn't show the current a/c heading, provides lateral guidance to achieve desired magnetic track relative to the beacon (independent of heading). Also indicates whether your position from/to the VOR depedent on the selected QDM (eg if you had a QDM of 270 selected when you are on the 270 radial it will show you are from the VOR, ie a QDM of 270 will take you away from the VOR not your heading).

 

https://www.youtube.com/watch?v=iCCk2ch-xL4

8

How does an aircraft use a DME?

The aircraft will send out a digital or analogue pulse train on one frequency which is received by the DME, the DME will then send back the same pulse train but on a different frequency back to the aircraft. Two frequencies are used so the aircraft don't interrogate each other and the pulse train is randomly generated so each aircraft will know when its own signal is being returned.

The time calculated between transmission of the first signal and receipt of the reply is used to work out the range of the DME. This will then be displayed in the cockpit for the pilot.

9

What is an ADF?

The ADF, or Automatic Direction Finder,

is an older type of a radio navigation instrument.

The needle indicates the relative position (bearing) of the NDB (Non Directional Beacon) to the nose of the aircraft.

Displays the bearing on an RBI

10

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

 

11

What is Radio Direction Finding?

Direction Finding (DF) or Radio Direction Finding (RDF) is the measurement of the direction from which a received signal was transmitted.

 

 

12

What is QTE?

The true bearing of an aircraft in relation to the Direction Finding Station, ie. the bearing the aircraft is as seen from the DF station.

13

What is QDR?

The magnetic bearing of an aircraft in relation to the Direction Finding Station, ie. the bearing the aircraft is as seen from the DF station.

14

What is QDM?

The Magnetic Heading to steer to make for the DF station, aka homing.

15

What are the methods by which an a/c can calculate its position using DF?

Triangulation

Pilots can establish their approximate position by obtaining two or more bearings from separate DF stations, and plotting the point at which the bearings intercept.

Homing

The procedure of using the DF equipment at your radio station with the radio bearing of an aircraft transmission, whereby the aircraft proceeds continuously towards the station following bearings obtained from your DF equipment.

DF Telecommunication Technique

Requesting the DF information from the DF station. Phraseology

“Station, Full C/s, request QDM/QDR/QTE, Full C/s”

response;

“C/s, Station, QDM/QTE/QDR 270 degrees class Bravo”

these requests can be refused but the reason must be stated.

ADF

The ADF works on the directional properties exhibited by a loop aerial, receiving signals from a ground based transmitter. (It is effectively an airborne DF unit)

Displays a Relative Bearing in relation to the aircraft’s heading using a pointer on an RBI. Whan RBI is added to the A/C heading you will get the QDM to the DF station.

RMI

An arrow is superimposed onto the compass rose so that a QDM can be read straight from the pointer.

The instrument can house more than one arrow to simultaneously display bearing information to more than one beacon.

16

What errors do NDB's suffer from?

Static Interference

Heavy precipitation and thunderstorms cause static interference. Often the ADF needle will point directly at the centre of an active TS in preference to the NDB.

Station Interference

Large bearing errors are caused by interference from transmitters operating on similar frequencies to the one being interrogated. Often caused by inaccurate tuning.

Mountain Effect

LF and MF are surface waves and therefore reflected by any high ground in their path. This can result in direct and reflected waves being simultaneously received by the aircraft and causing bearing errors. Normally overcome by flying higher.

Night Effect

Changes in the Ionosphere at night cause interference from transmissions, particularly in the higher medium frequencies, that would normally be out of range. Severe bearing errors are most likely to occur at sunrise and sunset.

Coastal Refraction

Radio waves travel slightly faster over the sea than they do over land. A radio wave crossing the coast at any angle other than 90º is going to be refracted. An aircraft flying over the sea and interrogating an NDB inland is likely to suffer a bearing error

Quadrantal Error

The airframe of an aircraft tends to reflect, refract and re-radiate incoming radio waves so the loop aerial receives a strong signal from the NDB together with a weaker one that has been distorted by the fuselage. Overall, the signal appears to bend towards the fuselage and this error is maximum when it arrives at the aircrafts quadrantal points. Conversely, signals arriving at the aircraft’s cardinal points do not suffer any error.

System Malfunction

Component or systems failure are difficult to detect because there is no failure warning device. Constant monitoring of the equipment is required

17

What is a True Radio Bearing?

A radio bearing for which the reference is True North

18

What is a magnetic Radio bearing?

A radio bearing for which the reference direction is Magnetic North.

19

What is the accuracy of a Class A DF?

+/- 2°

20

What is the accuracy of a Class B DF?

+/-5°

21

What is the accuracy of a Class C DF?

+/-10°

22

What is the accuracy of a Class D DF?

Worse than class C

23

What is Triangulation?

Pilots can establish their approximate position by obtaining two or more bearings from separate DF stations, and plotting the point at which the bearings intercept.

 

24

What is Homing?

The procedure of using the DF equipment at your radio station with the radio bearing of an aircraft transmission, whereby the aircraft proceeds continuously towards the station following bearings obtained from your DF equipment.

25

What is the DF Telecommunication Technique?

Requesting the DF information from the DF station. Phraseology

“Station, Full C/s, request QDM/QDR/QTE/QUJ, Full C/s”

response;

“C/s, Station, QDM/QTE/QDR/QUJ 270 degrees class Bravo”

these requests can be refused but the reason must be stated.

26

How would a pilot determine his position using an ADF?

Displays a Relative Bearing in relation to the aircraft’s heading using a pointer on an RBI. Whan RBI is added to the A/C heading you will get the QDM to the DF station. 

27

What is an RMI and how would you use it to navigate using DF?

Basically an ADF onto which arrows are superimposed onto the compass rose so that a QDM can be read straight from the pointer.

The instrument can house more than one arrow to simultaneously display bearing information to more than one beacon.

By adding the aircrafts heading to the Relative bearing to the station displayed on the RMI you can determine your QDM.

28

What are the advantages of using an NDB for navigation?

  • Reception is not limited to line of sight, MF waves propogate around the curvature of the earth
  • Maximum range is dependent on the power of the NDB

29

What are the disadvantages of an NDB?

  • The NDB is subject to atmospheric interference, coastal and night refraction, which affects accuracy
  • It is not as accurate as a VOR.

30

What is an ILS?

Instrument Landing System

The Instrument Landing System (ILS) is a highly accurate and dependable means of navigating to the runway in IFR conditions. When using the ILS, the pilot determines aircraft position primarily by reference to instruments. The ILS consists of:

A. The localizer transmitter;

B. The glide path transmitter;

C. The outer marker (or an NDB or other fix); and

D. In association with a suitable runway, the approach lighting system.

Has different categories

The localizer provides lateral guidance. The localizer is a VHF radio transmitter and antenna system using the frequency band as VOR transmitters (between 108MHz and 112MHz). Located at the upwind end of the runway.

The glide path transmitter provides vertical guidance to the pilot during the approach. The ILS glide slope is produced by a ground-based UHF radio transmitter and antenna system, operating in the 329.30 MHz to 335.00 MHz frequency band. Normally 300m from the threshold, also offset by 100-200m.

It is a precision approach.