Mode S Radar

Question 1

What year did new Transponders have to conform to Mode S?

Answer 1

1992

Question 2

What is Mode S elementary?

Answer 2

The capability to downlink aircraft identification directly to the ground ATC system.

Question 3

To fly IFR, does an aircraft require Mode S?

Answer 3

Yes, the requirement is for at least Elementary Mode S.

Question 4

Does each aircraft have a unique Mode S address?

Answer 4

Yes. A unique Mode S address is allocated for each aircraft by the state of registration.

Question 5

What is a benefit of Mode S selective interrogation?

Answer 5

Reduction of Fruiting and Garbling that provides higher integrity returns
The ability to offer datalink facility that can provide Downlink Aircraft Parameters (DAPs) such as speed, heading and altitude
ATCOs can co-ordinate with an adjacent centre without referring to Mode-A codes.

Question 6

Is SSR coverage limited by line of sight?

Answer 6

Yes

Question 7

Do Mode A/C and Mode S operate on the same frequencies?

Answer 7

Yes
Interrogations - 1030MHz
Replies - 1090MHz

Question 8

What are the two types of Mode S?

Answer 8

Elementary Mode S
Enhanced Mode S

Question 9

What is the Acquisition Phase of Mode S?

Answer 9

The interrogator tracks conventional transponders and looks for new Mode S transponders and retains the individual address for use during the Addressed Surveillance Phase.

Question 10

What is the Addressed Surveillance Phase of Mode S?

Answer 10

Mode S aircraft are interrogated individually for ATC identification, altitude information and exchange of other data using longer communication messages.

Question 11

What are the important capabilities of Mode S for ATCOs?

Answer 11

Altitude coded in 25ft increments
Indication whether aircraft is airborne or on the ground
Aircraft Identification used for Elementary Surveillance

Question 12

Describe Selective Interrogation

Answer 12

Using the unique address, ATCOs can set filters for relevant aircraft, rather than having a Radar screen cluttered with labels

Question 13

What are the operational improvements of Enhanced Mode S?

Answer 13

Automatic provision of airborne data to enhance ground systems functions including surveillance

Use of data link to improve efficiency of communications

Use of aircraft derived data for ground based safety nets

Enhance ATC decision support by using aircraft derived data

Improves the quality of surveillance

Question 14

What are the safety benefits of Enhanced Mode S?

Answer 14

Early recognition of aircraft manoeuvres

Detection of level busts

Reduction in risk of communication errors

Precise prediction of horizontal and vertical aircraft behaviour

The above improve safety in high density traffic areas through increased situational awareness.

Question 15

What are the capacity benefits of Enhanced Mode S?

Answer 15

Controller and aircrew workload reduction

RTF Reduction

Up-to-date aircraft parameters displayed to the ATCO

Extension of common knowledge between aircrew and controller

Reduced uncertainty concerning expected behaviour of the aircraft

Improvement of efficiency by allowing for more anticipation in traffic planning

Therefore, improvement of the capacity of sequencing in terminal sectors

Question 16

Describe Mode S Multilateration

Answer 16

Mode S MLAT provides accurate surveillance and identification of all transponder-equipped aircraft on the airport surface, on a dedicated screen.

In response to an MLAT interrogation, the transponder will transmit a reply that is received and processed by all of the MLAT sites. The position is calculated from the Time Difference of Arrival at the MLAT sites.

Question 17

Describe Mode S in TCAS

Answer 17

Two Aircraft Mode S exchange data for collision avoidance. The onboard computer predicts future positions and calculates the closest point of approach (CPA) and produces a two-level warning of proximity if necessary.

Question 18

What are the benefits of Active Multilateration Systems?

Answer 18

Independent of existing infrastructure
Improved Detection of Mode A/C Aircraft only
Complementary information to position
Increased Accuracy at long range