- In specific areas, ADS-B.
The air-to-air surveillance is in the interest of flight crews only. It provides the flight crew with:
-Assistance to build an aircraft environment awareness regarding external hazards (traffic, terrain, weather)
- Alerts against these external hazards.

1.1.2. SURVEILLANCE FROM THE AIR TRAFFIC CONTROLLER’S PERSPECTIVE
At the air traffic controller level, the surveillance may be either cooperative or non-cooperative, dependent or independent according to the type of the ground receiver and the aircraft equipment. Refer to 2 – Aircraft identification and position reporting for more details.

1.2. HOW TO READ THE BROCHURE?
It is agreed that there is a wealth of literature about aircraft systems available for pilots (e.g. FCOM, FCTM, CBT). Consequently, the present brochure does not supersede documents that already exist. The present brochure provides information to:
.  
Better understand how surveillance systems work

.  
Compare different surveillance systems that fulfill the same function

.  
Describe new surveillance systems expected in the near future.

1.2.1. SURVEILLANCE SYSTEMS AND FUNCTIONS
The present brochure describes surveillance systems from an operational perspective. Therefore, each chapter of the present brochure describes a surveillance function. Each surveillance function refers to one or several systems.
The 5 main surveillance functions are:
1.  
The Aircraft Identification and Position Reporting: The most commonly used system is the transponder coupled with a SSR. But other systems like ADS-C or ADS-B are available to fulfill this function.

2.  
The Traffic Surveillance: The well-known TCAS provides alerts and guidance to avoid aircraft that are too close. The ATSAW application clearly identifies surrounding aircraft and their characteristics (e.g. heading, speed, wake vortex category, etc).

3.  
The Terrain Surveillance: Enhanced Ground Proximity Warning System (EGPWS) and TAWS module of Traffic and Terrain Collision Avoidance System (T2CAS) are TAWS to prevent Controlled Flight Into Terrain (CFIT).

4.  
The Weather Surveillance: The weather radar detects and displays wet meteorological activities (i.e. clouds, precipitations, turbulence) on

Navigation Displays (NDs). The weather detection uses different methods (Autotilt, Multiscan, or 3D buffer) according to the manufacturer.

5.  
The Runway Surveillance: OANS displays the aircraft position on an airport map to improve the flight crew situational awareness. The ROW/ROP functions in conjunction with OANS provide warnings (visual and aural) and protection against runway end overruns. RAAS is a module of EGPWS and provides aural messages regarding the aircraft position on or out the runway.

These surveillance function can be combined in one single system. For instances:
　
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