Unit never seems to detect traffic.

If your unit never displays traffic and you suspect or can visually identify aircraft around you, your unit may need to be serviced. That having been said, you must understand that no collision avoidance system will detect every aircraft, even TCAS on board a commercial airliner. Here is a short list of reasons why the unit may not pick up the other aircraft:

• The other aircraft does not have a transponder, or it is not turned on.


• The other aircraft may not be being interrogated at that moment in time. Are they in RADAR shadow?


• If the belly of the aircraft is turned away from you, the output from their transponder antenna may be shadowed by their fuselage enough to cause your unit to think the aircraft is out of the detection window. Remember, RADAR sweeps can vary from 4 to 10 seconds, not constant, and it takes several replies for your unit to confirm the aircraft.

When designing PCAS, our engineers did not want a unit that would detect aircraft that was not confirmed. We have achieved what we believe to be a compromise between eliminating false signals while displaying as much traffic as possible.

A note about ATC
While ATC can provide invaluable services to you as a pilot, using them to verify aircraft displayed on the XRX screen may be unreliable. Remember, XRX is an airborne, dual network system capable of detecting aircraft responding to TCAS interrogations, or aircraft that are out of reach of Ground RADAR. A rule of thumb is, if the XRX is displaying traffic, the traffic must exist somewhere. Nothing else can generate the unique squawk and altitude codes used in sensing traffic.