WARNING: the functionalities described in this section are experimental and have never been fully tested. Use with care !
The TCAS (Traffic Collision Avoidance System) is used on civil aircraft to reduce the incidence of mid-air collisions. The principle is to monitor the airspace around the aircraft, warn the pilot and provide conflict resolution indication. For the Paparazzi system, a light version of a TCAS-inspired system has been implemented. It can send warning to the ground station and if nothing is done, it takes control of the vertical loop in order to have a minimum vertical separation. This TCAS monitors all the aircrafts based on the traffic information send by the Server and it resolve conflicts only with one aircraft at a time.
When the system detects a possible collision, the TCAS logic follows the rules:
- if other_AC_alt > AC_alt + alt_limit then the AC goes down (alt_setpoint = MIN(nav_alt, other_AC_alt - alt_limit))
- if other_AC_alt < AC_alt - alt_limit then the AC goes up (alt_setpoint = MAX(nav_alt, other_AC_alt + alt_limit))
- else the AC with the smallest ID goes down
- alt_setpoint is bounded by (ground_alt + security_height)
The control of the TCAS will be active until the conflict is solved, no longer exist or a timeout occurs.
Activate TCAS service
The traffic_info service must be activated with the TCAS:
ap.CFLAGS += -DTRAFFIC_INFO -DTCAS ap.srcs += traffic_info.c tcas.c
The TCAS system is operational only in AUTO2 and in altitude mode. The system is inhibited under the security height.
<section name="TCAS" prefix="TCAS_"> <define name="TAU_TA" value="10." unit="s"/> <define name="TAU_RA" value="6." unit="s"/> <define name="ALIM" value="15." unit="m"/> <define name="DT_MAX" value="2000" unit="ms"/> </section>
- TAU_TA: traffic advisory in second. A warning message is send to the ground and displayed in the alert page of the GCS if the estimated time before a collision is below TAU_TA. Default = 2*CARROT.
- TAU_RA: resolution advisory in second. A warning message is send to the ground (+ display in GCS) and the system takes control over the altitude setpoint of the vertical loop if the estimated time before a collision is below TAU_RA. Default = CARROT.
- ALIM: altitude limit in meters. The minimum vertical separation between two aircraft. Default = 10.
- DT_MAX: lost comm or timeout in ms. Timeout to interrupt a TA or an RA if data are not received. Default = 1500.