# Air Traffic Avoidance: UAS Traffic Management (UTM)
PX4 can use MAVLink
UTM_GLOBAL_POSITION (opens new window) messages to support simple air traffic avoidance in missions.
If a potential collision is detected, PX4 can warn, immediately land, or return (depending on the value of
# Configure Traffic Avoidance
Configure the trigger distance and action when there is a potential collision using the parameters below:
|NAV_TRAFF_AVOID||Enable traffic avoidance mode specify avoidance response. 0: Disable, 1: Warn only, 2: Return mode, 3: Land mode.|
|NAV_TRAFF_A_HOR||Horizonal radius of cylinder around the vehicle that defines its airspace (i.e. the airspace in the ground plane).|
|NAV_TRAFF_A_VER||Vertical height above and below vehicle of the cylinder that defines its airspace (also see NAV_TRAFF_A_HOR).|
|NAV_TRAFF_COLL_T||Collision time threshold. Avoidance will trigger if the estimated time until collision drops below this value (the estimated time is based on relative speed of traffic and UAV).|
PX4 listens for
UTM_GLOBAL_POSITION MAVLink messages during missions.
When a valid message is received, its validity flags, position and heading are mapped into the same
transponder_report UORB topic used for ADS-B traffic avoidance.
The implementation is otherwise exactly as described in: ADS-B traffic avoidance > Implementation.
UTM_GLOBAL_POSITION (opens new window) contains additional fields that are not provided by an ADSB transponder (see ADSB_VEHICLE (opens new window)). The current implementation simply drops the additional fields (including information about the vehicle's planned next waypoint).