Comms (14-05-18)

Question 1

What is the range of HF comms and why?

Answer 1

Very long range due to the refraction properties in the ionosphere.

Leads to a clarity trade off.

Question 2

What is the frequency band of HF comms?

Answer 2

2-22MHz

Question 3

What is the frequency band of VHF comms?

Answer 3

118 - 137MHz

Question 4

What is the frequency band for NAVAIDs?

Answer 4

108 - 118MHz

Question 5

What is SELCAL?

Answer 5

A system used to allow ATC to indicate that they are trying to contact an A/C

Question 6

When does SELCAL have to be checked/changed?

Answer 6

On first contact with a new ATC

Question 7

What is SATCOM?

Answer 7

Satellite communications operated by INMARSAT via 4 geostationary satellites giving covereage between 80degN - 80degS

Question 8

What are ACARS?

Answer 8

Aircraft Communication Addressing and Reporting System

VHF data link that automatically passes info about engine and Nav data within organisation.

Question 9

What is CPDLC?

Answer 9

Controller Pilot DataLink Comms

Uses ACARS to pass ATC clearances and communications to the crew via FMS

Question 10

What is VDF?

Answer 10

VHF direction finding.

Question 11

When using VDF, what is variation and when is it applied?

Answer 11

Variation is the difference between mag and true north and it is applied at the station.

Question 12

What did old VDF systems use?

Answer 12

adcock aerials and sense aerials

Question 13

What do modern VDF systems use?

Answer 13

Array of vertical dipoles all connected to a central receiver.

Question 14

What are the classification of VDF systems?

Answer 14

By accuracy:

Class A - +/- 2deg

Class B - +/- 5deg

Class C - +/- 10deg

Class D - >+/- 10deg

Question 15

What is the emergency frequency?

Answer 15

121.5MHz

Question 16

What does the approach procedure code QDM mean?

Answer 16

Follow A/C mag heading to station.

Question 17

What does the approach procedure code QDR mean?

Answer 17

Follow mag bearing from station (reciprocal to QDM)

Question 18

What does the approach procedure code QUJ mean?

Answer 18

Follow true track to station. (true to union jack)

Question 19

What does the approach procedure code QTE mean?

Answer 19

Follow true bearing from station (reciprocal to QUJ)

Question 20

What are the errors associated with VDF?

Answer 20

Ground reflected waves (vertical plane) - causing destructive interference

Multipath error (horizontal plane) - causing destructive interference

Cone of confusion

Synchronous transmissions - 2 A/C transmitting at once

Intervening high ground

Super-refraction; sub-refraction; sporadic E