Background, Overview and Functionality

1. Secondary Surveillance Radar,
Mode-S & ADS-B

2. • KZA 1907 / IL 76
• CHIMKENT - DELHI
• CLEARED TO DESCEND
150
• 37 PASSENGERS
• SVA763 /TYPE – B 747
• DP-DAHRAN
• ATD- 1832
• CLEARED AT FL 140
• 312 PASSGENGERS
Charkhi Dadri IGI AIRPORT
100 KM
DATE : 12 NOV 1996 / 1830-45
IST
PLACE : DELHI
AREA
INCIDENT : MID AIR
COLLISSION
TOTAL HUMAN LIFE
LOST : 349
AVOIDABLE !!!!
FL 150 FL 140

3.  Lahoti Commission (HC Judge Ramesh Chandra
Lahoti)
 Evidence lead to blame to KZA 1907 who descended
to 145140 and even lower when cleared for FL 150
 Further Lack of SSR at IGI (It had only a PSR)
 Only one corridor for civil arrival & departure
 Airborne collision avoidance system was not avbl
 FDR evidence suggested KZA 1907 could not decipher
ATC instructions & warning of reciprocal
Aftermaths

4.  Strict Regulation enforced wef 01 Jan 2001
 IGI provided with SSR; Separate corridor earmarked for
arrival & departure
 No ac with passenger capacity >30 to be permitted
without Mode ‘S’ transponder in addition to Mode A & C
 No ac with passenger capacity 10-19 to be permitted
without Mode ‘A’ & ‘C’ transponder
 Twin Jet with passenger capacity of <10 not permitted
without Mode ‘A’ & ‘C’ transponder
 No helicopter is permitted if not equipped with Mode ‘A’ &
‘C’ transponder
Aftermaths

5.  Background
 Modes & Codes
 Glimpses of SSR
 Typical IFF Transponder
 Some IFF Jargons
 Mode S: Overview, Functionality & Advantages
 ADS-B: Overview, Functionality & Advantages
 Glimpses of ADS-B operation
Coverage

6.  Identification, friend or foe (IFF) is an identification
system designed for command and control.
 It enables military and national (civilian air traffic
control) interrogation systems to identify aircraft,
vehicles or forces as friendly and to determine their
bearing and range from the interrogator.
 IFF may be used by both military and civilian aircraft.
Background

7.  IFF was first developed during the Second World War,
with the arrival of radar for protection of British isles
and was called ‘Parrot’
 The first active IFF transponder
(transmitter/responder) was the 'IFF Mark I' and was
put into operation in 1939.
 IFF Mark II, changed the tuned frequency, sweeping it
through the bands being used by the various radars.
Background

8.  The United States and other NATO countries started
using a system called Mark XII in the late twentieth
century
 In 1940, Mark III transponders were designed to
respond to specific 'interrogators', rather than
replying directly to received radar signal
Background

9. Mode P1-P3
Interval
Use Remarks
1 3 Mil 2-digit octal mission code
2 5 Mil 4-digit octal unit code; Mil Authentication
Set on Ground, Ac like C-17 can change in flight
3/A 8 Civ/ Mil 4-digit octal identification code for the aircraft,
assigned by the air traffic controller.
B 17 Civ Reserved for use by civil ATC
C 21 Mil/ Civ Provides ac pressure altitude from ISA 1013.2 mb
D 25 Civ Not in use
4 13 Mil 3-pulse reply, delay is based on the encrypted
challenge
5 N/K Mil/ Civ Provides a cryptographically secured version of
Mode S and ADS-B (GPS position)
Modes & Codes

10. A Typical IFF Transponder

12.  Garble- One Ground Station interrogates 2 or more ac resulting
into intermingles / overlapped replies
 Fruit – One ac interrogated by 2 or more Ground Station,
transponder retriggered resulting into long unreadable reply
 Passive Decoding – code mode present in Radar; produces a
code match slash on PPI
 Active Decoding- Ac is designated by pointing device on scope,
replies are decoded by radar and displayed
 Mode Interlacing- Txr of different modes that can be changed
with each PRF. A max of three modes can be interlaced in one
pulse
Some Jargons

13. Mode-S

14.  Allows selective interrogation of aircraft according to the unique
24-bit address assigned to each aircraft
 Employs ground-based interrogators and airborne transponders
and operates in the same radio frequencies (1030/1090 MHz)
 The position and identification data supplied by Mode S/ADS-B
broadcasts are available to pilots and air traffic controllers.
 ICAO Regulation (EU) No 1207/2011 requires that all flights
operating as general air traffic in accordance with instrument
flight rules within the EU are equipped with mode S
transponders
Mode-S Overview

15.  Automatic reporting of aircraft identity. This is the aircraft
callsign used in flight which is automatically presented to
the controller
 Altitude reporting in 25ft intervals (subject to aircraft
capability)
 Flight status (airborne / on the ground)
 Roll Angle, True Track Angle and Track Angle Rate
 Ground Speed
 Magnetic Heading
 Indicated airspeed (IAS) and Mach-number
Mode-S Functionality

16.  Improved situation awareness.
 Progressive reduction of R/T workload per flight
 Safety enhancement
 Unambiguous aircraft identification
 Improved integrity of surveillance data
 Alleviation of Mode 3/A code shortages
 Improvements to Safety Nets
Mode-S Advantages

18.  ADS-B is a Surveillance technique that relies on aircraft or
airport vehicles broadcasting their identity, position and
other information derived from on board systems
 ADS-B is automatic because no external stimulus is
required
 It is dependent because it relies on on-board systems to
provide surveillance information to other parties
 Data is broadcast, the originating source has no
knowledge of who receives the data and there is no
interrogation or two-way contract.
ADS-B Overview

19.  Aircraft horizontal position (latitude/longitude)
 Aircraft barometric altitude (will be the same as for
the SSR)
 Quality indicators Aircraft identification: Unique 24-bit
aircraft address
 Aircraft identification
 Mode A code
 Emergency status
ADS-B Functionality

20.  Full “Network-wide” Surveillance coverage
Surveillance “everywhere”, i.e. no gaps from gate-to-
gate
 Air-to-air Surveillance possible, i.e. traffic situational
awareness picture available on board
 The aircraft is integral part of the Network
 Surveillance data provided directly from on-board
systems
 High performance
ADS-B Advantages

21.  Improved safety
 Increased capacity
 Environmental sustainability (CO2 reduction)
 ADS-B is currently being, or already has been,
implemented in North America, Europe and other
areas worldwide including the Asia/Pacific region.
 ICAO has made ADS-B a mandatory requirement for
all flights wef 01 Jan 2020
ADS-B Advantages

22. Thank You for Flying Safe ! ! !