Traffic awareness and collision avoidance

Why is a nearby target not always the greatest threat?

Closure and relative height matter as well as displayed distance.

Cooperative surveillance has limits

ACAS II is the collision-avoidance standard associated with TCAS II installations. It relies on cooperative transponder information and interrogation/coordination functions. A target needs suitable functioning equipment to be detected in the intended way; altitude reporting is needed for the vertical information supporting resolution logic. A non-displayed target is therefore not proof that the surrounding airspace is empty.

The traffic display shows relative geometry, relative altitude and trends according to its symbology. It is not a reliable source of an intruder’s horizontal heading or a clearance to manoeuvre. Range filters and high-density processing can change what is displayed. Distinguish a traffic information symbol, proximate traffic, a traffic advisory and a resolution advisory rather than treating every mark as the same threat level.

Predict a closing encounter

A simple teaching measure of urgency is time to closure: distance divided by closing speed when the geometry is directly closing at a steady rate. At 6 NM and 600 kt relative closure, that time is 36 seconds. A nearer aircraft moving away may be less urgent than a more distant aircraft closing rapidly. Real ACAS logic also considers vertical separation, sensitivity, tracking and protective thresholds.

The laboratory calculates only a synthetic straight-line closure time and relative altitude. It does not reproduce certified threat logic or generate an operational TA/RA. Change closing speed while preserving distance and observe the time. Then preserve closure time while changing height difference to see why the same horizontal urgency can describe different vertical relationships. Continue normal lookout, ATC and aircraft procedures; a display is one information source with specified limitations.

How do you follow the actual resolution advisory immediately?

Some advisories require maintaining or limiting a rate, rather than a reflexive climb.

Awareness and resolution are different functions

A traffic advisory attracts attention and supports preparation and visual acquisition. It does not itself provide resolution guidance that justifies an evasive manoeuvre solely from the traffic display. A resolution advisory supplies vertical guidance, which may demand a change, a restriction or maintenance of the present vertical behaviour. Reacting to every RA by instinctively climbing can therefore contradict the actual advisory.

When both aircraft have compatible ACAS equipment, coordination supports complementary resolution guidance. This does not make the system an ATC separation service or guarantee a particular minimum separation in every encounter. Inhibitions and available guidance depend on flight condition, height and system design. Know the installed system’s normal, degraded and coupled functions rather than assuming all aircraft have the same autopilot/flight-director relationship.

Follow the actual guidance and procedure

Identify the actual resolution advisory and respond immediately using the approved aircraft and operating procedure, unless doing so would jeopardise safety under the applicable rules. Inform ATC as required and manage the return to the appropriate clearance after the conflict. Some approved installations provide automatic or flight-director coupling; others require manual control. Training must reflect the actual equipment rather than a universal claim that every RA is flown in the same way.

Do not infer a safe horizontal escape direction from the displayed location or apparent motion of an intruder. The display geometry and track limitations do not support that assumption. The preceding closure model illustrates relative motion; it does not calculate a TA, an RA or an operational manoeuvre command. Follow the actual RA without delay, monitor the aircraft response, and make the required SOP callouts without delaying the manoeuvre. A verbal explanation is a training discussion, not a prerequisite for responding in flight.

Can you explain and apply the mechanism?

Four original questions. Work from the stated facts, then compare your reasoning with the explanation.