Expert: Heiko Hanusch - 12/2/2005

Question
Capt. Hanusch,

I have a question on the TCAS. When are solid circles and squares depicted on the ND beside the altitude of the conflicting traffic and what do these symbols imply?
For instance, -09 with an up arrow would imply that traffic is 900 feet below and climbing. Now, if there were a square, a circle or a diamond beside it, what would that imply?
Would you also briefly explain what DMOD and tau mean?

Thank you Sir.

Answer
Hi Jascha,

Thanks for your question,

Solid red square means    Resolution Advisory (computer will tell you which way to go to avoid intruder)

Solid amber circle means  Traffic Advisory ( computer will ony tell you that there is traffic but no resolution is given)

Solid blue diamond        Proximate Traffic (vicinity only, no threat)

If you watch traffic on the TCAS display the order would appear in the following: blue diamond, yellow circle, red square

there are some other symbols as well (hollow) which indicate other transponder reply traffic but are not critical.
An up or down arrow only appears if the traffic is climbing or descending at more than 500 ft/min.

I hope this helps.

Have a great day,

H2