TA

A TA (traffic advisory) is the lower-level warning issued by TCAS (Traffic Collision Avoidance System) when an aircraft has detected another aircraft at a distance or altitude that warrants attention, but not yet an immediate evasive maneuver. The system alerts the flight crew with an aural announcement, a visual symbol on the cockpit display, and written text like TRAFFIC or TRAFFIC TRAFFIC, depending on the threat level and proximity. A TA tells pilots to look for the target aircraft and prepare to maneuver if necessary; it does not command a specific action.

TCAS generates TAs when intruders fall into defined threat zones based on range, altitude separation, and closure rate. The exact thresholds vary by TCAS version and mode. TCAS I (older, minimal equipment) may issue TAs only at higher altitudes. TCAS II and TCAS III (more capable) use more complex algorithms and can issue TAs across wider altitude bands and at greater ranges. A TA typically appears when an intruder is between roughly 2,000 and 5,000 feet away, though this depends on vertical separation and relative speed.

TA vs. RA: the crucial distinction

The key distinction is that a TA is advisory; an RA (resolution advisory) is mandatory guidance. An RA tells a pilot to climb or descend at a specified rate or range. TAs do not command vertical movement. If the threat increases, closure rate rises, separation shrinks, TCAS may escalate a TA to an RA. Not all TAs become RAs; many resolve when the aircraft diverge naturally or the intruder passes without further hazard.

In maintenance and avionics, TAs matter because they reveal whether the TCAS is functioning at all and whether its threat logic is sound. During ground testing or after repairs, technicians verify that TCAS triggers TAs at expected ranges and altitudes using test vectors or functional checkout procedures. Nuisance TAs (alerts for aircraft that pose no real threat, such as very distant or non-conflicting targets) can degrade crew confidence, so system performance and sensor calibration are critical.

The term traffic advisory reflects the system's purpose: advising pilots of traffic, as opposed to commanding evasive action (which is what an RA does). The terminology is baked into international standards and avionics documentation, and every commercial crew is trained to recognize and respond appropriately to a TA well before it might become an RA.