A320 IN N90'S AIRSPACE EXPERIENCED TCASII RA WITH UNKNOWN ACFT.

Narrative

1) SITTING ON JUMPSEAT; EARPLUGS BEING USED; SPEAKERS LOW; WITH HEADSETS BEING USED BY PF (CAPT) AND FO. I WAS NOT USING A HEADSET. 2) AT 12000 FT THE CTLR GAVE THEM A DSCNT TO 7000 FT AND ASKED THE CREW TO 'EXPEDITE.' FLT CREW HAD BEEN FLYING A GOOD; DISCIPLINED FLT EXCEPT FOR 1 MINOR DEV (EXCEEDING 250 FT BELOW 10000 FT) DURING THE DSCNT; WHICH WAS MENTIONED BY ME AND IMMEDIATELY CORRECTED BY THE PF. (I WAS ONLY PICKING UP ABOUT 2/3 OF RADIO TFC AS I WAS RETURNING TO NEW YORK CITY AT THE END OF MY TRIP AND WAS TIRED.) 3) FLT CREW DID NOT HAVE TCASII TFC DISPLAYED BUT HAD A TCASII MODE ENABLED WHICH ONLY SHOWED THREATS. 4) SHORTLY AFTER LEVELING AT 7000 FT; WE GOT A TA FROM THE TCASII WHICH SHOWED TFC AT +01 (100 FT ABOVE) AND LEVEL AT OUR 12:30-1 O'CLOCK POS AND CLOSING. THE FO INCREASED THE SCALE AND IT BECAME APPARENT THAT TFC WAS INSIDE THE 5 NM RANGE. SHORTLY THEREAFTER (10? SECONDS) AN RA WAS ISSUED WHICH I BELIEVE WAS 'CLB; XING CLB' FOLLOWED ABOUT 3-4 SECONDS LATER WITH A REVERSAL; 'DSND; DSND NOW.' (20% CHANCE THAT IT COULD HAVE BEEN OPPOSITE COMMANDS AS IT HAPPENED SO QUICKLY.) 5) CAPT HAD DISCONNECTED THE AUTOPLT AND WAS TRYING TO RESPOND TO TCASII COMMANDS AND ALSO STARTED A L TURN. AT THIS TIME I SPOTTED TFC (PROBABLY THE CAPT TOO) IN A 30 DEG L TURN AND ROLLING OUT SO THAT HE WAS WINGS LEVEL WHEN WE PASSED EACH OTHER. APPARENTLY THE OTHER ACFT (A LOW WING; WHITE; LIGHT TURBOPROP OR MAYBE JET) HAD SPOTTED US FIRST. TIME FROM OBSERVING ACFT TO PASSING BY EACH OTHER WAS ABOUT 4 SECONDS. A) OBVIOUSLY EITHER APCH MISTAKENLY GAVE US 7000 FT OR THE OTHER ACFT WAS AT THE WRONG ALT. B) THE FLT CREW WAS DOING A GOOD JOB; BUT APPEARED TO HAVE SOME COMPLACENCY WITH REGARDS TO AUTOMATION. (THIS WAS THE END OF THEIR FLYING THAT DAY SO EITHER FATIGUE; OR SEVERE COMPANY LABOR MGMNT PROBS ARE POSSIBLE FACTORS HERE.) C) THEY COULD ALSO HAVE HELPED THEMSELVES BY HAVING TFC DISPLAYED IN THE TERMINAL AREA. THIS IS A GOOD TECHNIQUE AND ONE THAT I ALWAYS USE. D) NO DISCUSSION ENSUED WITH EITHER OTHER ACFT OR CTLR. E) MY ASSUMPTION IS THAT OTHER ACFT WAS ON DEP SINCE IT WAS HEADING SBOUND; S OF THE ARPT.