Airborne Collision Avoidance System (ACAS)

Airborne Collision Avoidance System (ACAS)

1. Operates independently of ground-based equipment and air traffic control

2. Warning pilots of the presence of other aircraft that may present a threat of collision

3. System initiates a maneuver that will reduce the risk of collision if risk is imminent

4. Describe short-range systems intended to prevent actual metal-on-metal collisions

5. Difference of ASAS (airborne separation assurance system)

   • Describe longer-range systems
   • Maintain standard en route separation between aircraft (5 nautical miles (9.3 km) horizontal and 1,000 feet (300 m) vertical)

6. Implementations that meets ACAS II standards set by ICAO

   • TCAS II (Traffic Collision Avoidance System)
     • Version 7.0
     • Version 7.1

7. Collision Avoidance System

   • Airborne radar
     • Detect relative location of other aircraft
   • Traffic collision avoidance system (TCAS)
     • Actively interrogates the transponders of other aircraft via 1.03 GHz radio frequency
       • Independent of air traffic control
       • Reply via 1.09 GHz
       • Occur several times per second
     • Negotiates collision-avoidance tactics in case of a threat
       • Negotiating mutual avoidance manoeuver
         • Manoeuvers are restricted to changes in altitude & modification of climb/sink rates
     • Effective in avoiding collisions only with other aircraft
       • Equipped with functioning transponders with altitude reporting
       • Correctly operating mode C or mode S transponder
         • Unique 24-bit identifier assigned to each aircraft that has a mode S transponder
     • Mandated by ICAO
       • To be fitted to all aircraft with a maximum take-off mass (MTOM) of over 5,700 kg (12,600 lb) or authorized to carry more than 19 passengers
         • TCAS I
           • Installed on aircraft 10-30 passengers
         • TCAS II
           • Installed on aircraft > 30 passengers
     • Based on secondary surveillance radar (SSR) transponder signals
       • Operate independently of ground-based equipment
     • Display on Navigation Display or Electronic Horizontal Situation Indicator (EHSI)
     • Builds 3D map of aircraft in airspace
       • With range from interrogation and response round trip time
       • Altitude reported by interrogated aircraft
       • Bearing (directional antenna from response)
       • Extrapolating (Estimate) to anticipate future values for potential threat
     • Protected volume of airspace
       • Size depends on depends on the altitude, speed, and heading
         • Higher altitude & higher speed, larger sensitivity level, larger protected airspace
   • Portable Collision Avoidance System (PCAS)
     • Less expensive
     • Passive version of TCAS
       • Do not actively interrogate the transponders of other aircraft
       • Listen passively to responses from other interrogations
       • Same limitations as TCAS
   • FLARM
     • Small size, low power device
     • Commonly used in gliders, light aircraft
     • Broadcasts own position and speed vector obtained from integrated GPS
       • Over license-free ISM band radio transmission
       • Listens to other devices based on the same standard at same time
         • Warn pilot accordingly by acoustical and visual means
     • Incorporates high-precision WAAS 16-channel GPS receiver & integrated low-power radio transceiver
     • Static obstacles included in FLARM's database
     • No warning is given if aircraft does not contain additional FLARM device
   • Ground Proximity Warning System (GPWS)
     • Radar altimeter to detect proximity to ground or unusual descend
   • Terrain awareness and warning system (TAWS)
     • Uses digital terrain map, together with position information from a navigation system (GPS)
       • Predict aircraft's current flight path could put it in conflict with obstacles such as mountains or high towers
       • That cannot be detected by GPWS
   • Synthetic vision
     • Computer-generated simulation of their outside environment for use in low or zero-visibility situations
     • Information used to present warnings is often taken from GPS, INS, or gyroscopic sensors
   • Obstacle Collision Avoidance System (OCAS)
     • Ground based system
     • Low powered radar mounted on or near the obstacle
     • Radar detects aircraft in the proximity of the obstacle
       • Firstly, warns aircraft via flashing medium intensity lights
       • Secondly warns aircraft of the obstacle via a VHF broadcast
     • No additional equipment onboard aircraft required