(Reference: Page 23 FAA TCAS-II guilines)
The TCAS table provides distinct tau values for the Traffic advisory (TA) and resolution advisory (RA) zones. Based on these values, one would expect the protected volume to take the shape of a circle when viewed from the top. However, upon further examination of figures provided by the FAA FAA-TCAS-II or on Wikipedia, it appears that the TA and RA zones are actually represented as ellipses. Wikipdia TCAS
Can anyone provide insight on the reason for the TA and RA zones being represented as ellipses instead of circles and the methodology used to determine these ellipses?
Edit: Based on the discourse in the comments section, it has been determined that the zones in question should adopt an elongated shape oriented in the direction of heading, as opposed to a circular shape. Despite this conclusion, the issue of determining the precise shape remains unresolved. It is imperative to consider multiple parameters in order to accurately determine the shape, and the utilization of specific methods or equations may prove beneficial in this regard.