TCAS warnig range

[OscarTango]

Today I saw a loss of seperation happening. Aircraft A at FL330, aircraft B at FL290 cleared up to FL 320 about 5 miles ahead of Aircraft A, but slower. Aircraft B mistook a call for a company ship with similar callsign and climbed to FL330. Of course our STCA went off as soon as he busted FL322 and he was given the instrcution to descend immediatly. Traffic info was given to Aircraft A... his reply : we saw him on the TCAS, but he wasnt in the "warning area",... distance was around 3 miles . My question : how far ahead of the aircraft does the "warning area" stretch ? I think I remember that TCAS take into account closing speed, but I'm not sure about it. if so, in this case the speed diffence was about 30 knots ground speed... and that would explain why the TCAS didn't issue a traffic warning.


Can somebody shine the light please ?

[BIK_116.80]

A 30 knot closure rate at 3 miles range would take six minutes to closest point of approach. In TCAS terms - that’s forever.

TCAS knows nothing about ATC separation minima. TCAS works in terms of time to closest point of approach.

Non Threat Traffic

The other aircraft is displayed as an open diamond shape, along with its relative pressure altitude. The other aircraft is not considered a threat.

Proximity Intruder Traffic

The other aircraft symbol changes to a solid diamond to indicate that the intruder is within plus or minus 1200 feet vertically and within 6 miles range, but is still not considered a threat.

Traffic Advisory (TA)

The intruder symbol turns into a yellow circle and an aural “TRAFFIC TRAFFIC” is issued. Time to closest point of approach is dependent upon altitude and varies between 20 and 48 seconds. At a 30 knot closure rate 20 seconds equates to 0.16 nautical miles, and 48 seconds equates to 0.4 nautical miles.

Resolution Advisory (RA)

The intruder symbol turns red and an aural instruction is issued, eg “DESCEND DESCEND” or “CLIMB CLIMB”. Time to closest point of approach is dependent upon altitude and varies between 15 and 35 seconds. At a 30 knot closure rate 15 seconds equates to 0.125 nautical miles and 35 seconds equates to 0.29 nautical miles.

Refer Honeywell TCAS II User’s Manual (http://www.honeywelltcas.com/products_pages/cas81_6mcu/cas81_pilotguide.pdf)
PDF pages 12 thru 16, original document pages 9 thru 13.