ADS & MLAT

Question 1

What is ADS?

Answer 1

Automatic Dependant Surveillance

AUTOMATIC
Because no external stimulus is required.
DEPENDENT
Because it relies on on-board systems to provide.
SURVEILLANCE
information to other parties.

Question 2

What does ADS do?

Answer 2

A means by which aircraft, aerodrome vehicles and other objects can automatically transmit
and/or receive data such as identification, position and additional data, as appropriate, in a
broadcast mode via a data link.

Question 3

What is ADS-B?

Answer 3

BROADCAST
The originating source (AC) has no knowledge of who
receives the data and there is no interrogation or two-way contract.

Question 4

What information does ADS B give?

Answer 4

Horizontal position
Vertical position
Velocity (Speed)

as well as other information.

Question 5

What is ADS-C?

Answer 5

ADS-C
“Contract”

Question 6

What 3 types of contracts are there for ADS?

Answer 6

Periodic contract. (Constant, every 20 mins)
Demand contract.
Event contract. (Crossing FIR Boundary)

Question 7

How does ADS-C work?

Answer 7

Logon request, the ATSU will have to establish ADS Contract(s) with the AC before it can receive ADS reports.

Question 8

What is MLAT?

Answer 8

Multi-Lateration
Similar technology to ADS.

Question 9

How does MLAT work?

Answer 9

Multiple MLAT Antennae on the ground receive broadcasts from AC and Vehicle Mode S Transponders.
Use a system process called Time Difference of Arrival (TDOA) to determine accurate positions of AC or Vehicles

Question 10

How can MLAT data be displayed?

Answer 10

Positions can be displayed on ATC surveillance screens in a similar manner to data derived from radar or ADS-B.

Question 11

What are the MLAT Limitations?

Answer 11

Similar to SSR and ADS - only detects aircraft or
vehicles with Mode S transponders

Question 12

What are the MLAT Limitations?

Answer 12

Similar to SSR and ADS - only detects aircraft or
vehicles with Mode S transponders

Question 13

What are the requirements for ADS-B Out?

Answer 13

• GPS navigation capability.
• Mode-S Transponder.
• Avionics capable of providing correct data (usually comes with Enhanced Surveillance capability).
• Correct connections between the three.

Question 14

Three types of primary messages sent by ADS-B?

Answer 14

Three Primary Types – Regular Broadcast (Always)
Position (Surface and Airborne)
Airborne Velocity
Aircraft Identity

Question 15

Accuarcacy of ADS?

Answer 15

• Maximum Accuracy Category is 7.5m.
• Minimum Accuracy Category is >20NM