TCAS was added as part of the PMDG 737NG 800/900 package and also adds
this functionality to the PMDG 737 600/700 when installed. The
original PMDG 737NG 600/700 did not have TCAS as part of the package.
To activate the TCAS after upgrading, turn the selector on the Radio
Management Panel Transponder to the TA/RA position and then depress the
TFC button on the EFIS control panel to see the range rings.