Narrative:

Aircraft #4 was northbound at FL290. 3 other aircraft sbound at FL310 and all 3 had TCASII events with aircraft #4 when they came in close proximity. Aircraft #2 responded to TCASII RA and descended but did not lose separation. Aircraft #3 received an RA but did not change altitude. Aircraft #1 responded to the RA and descended to FL302, separation was lost between aircraft #1 and aircraft #4. Our equipment showed no abnormal altitude information from aircraft #4. Supplemental information from acn 292824: the ATC controller speculated that the C-9 may have been the intruder aircraft although his assigned altitude of FL290 was confirmed by the crew. Erroneous encoded altitude information from that aircraft may have been responsible for causing the RA's according to the controller. In my opinion TCASII performed its function as it was designed to do. Human factors may have been involved if an altimeter was improperly set. Both of our altimeters were verified set at 29.92 as appropriate for flight at high altitude. Official TCASII event form has been filed. Supplemental information from acn 293125: flying at FL310 autoplt engaged, VNAV and LNAV selected. TCASII showed a target at FL290, we were heading south on J121. As aircraft got within 10 NM, another target appeared at plus 100 ft, followed by a TA then an RA. Captain assumed control of aircraft and began a shallow left turn and descended to approximately FL303 at which time the RA disappeared. In my opinion there was a malfunction in aircraft #4's transponder causing false TCASII returns.

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Original NASA ASRS Text

Title: TCASII INCIDENT.

Narrative: ACFT #4 WAS NBOUND AT FL290. 3 OTHER ACFT SBOUND AT FL310 AND ALL 3 HAD TCASII EVENTS WITH ACFT #4 WHEN THEY CAME IN CLOSE PROX. ACFT #2 RESPONDED TO TCASII RA AND DSNDED BUT DID NOT LOSE SEPARATION. ACFT #3 RECEIVED AN RA BUT DID NOT CHANGE ALT. ACFT #1 RESPONDED TO THE RA AND DSNDED TO FL302, SEPARATION WAS LOST BTWN ACFT #1 AND ACFT #4. OUR EQUIP SHOWED NO ABNORMAL ALT INFO FROM ACFT #4. SUPPLEMENTAL INFO FROM ACN 292824: THE ATC CTLR SPECULATED THAT THE C-9 MAY HAVE BEEN THE INTRUDER ACFT ALTHOUGH HIS ASSIGNED ALT OF FL290 WAS CONFIRMED BY THE CREW. ERRONEOUS ENCODED ALT INFO FROM THAT ACFT MAY HAVE BEEN RESPONSIBLE FOR CAUSING THE RA'S ACCORDING TO THE CTLR. IN MY OPINION TCASII PERFORMED ITS FUNCTION AS IT WAS DESIGNED TO DO. HUMAN FACTORS MAY HAVE BEEN INVOLVED IF AN ALTIMETER WAS IMPROPERLY SET. BOTH OF OUR ALTIMETERS WERE VERIFIED SET AT 29.92 AS APPROPRIATE FOR FLT AT HIGH ALT. OFFICIAL TCASII EVENT FORM HAS BEEN FILED. SUPPLEMENTAL INFO FROM ACN 293125: FLYING AT FL310 AUTOPLT ENGAGED, VNAV AND LNAV SELECTED. TCASII SHOWED A TARGET AT FL290, WE WERE HDG S ON J121. AS ACFT GOT WITHIN 10 NM, ANOTHER TARGET APPEARED AT PLUS 100 FT, FOLLOWED BY A TA THEN AN RA. CAPT ASSUMED CTL OF ACFT AND BEGAN A SHALLOW L TURN AND DSNDED TO APPROX FL303 AT WHICH TIME THE RA DISAPPEARED. IN MY OPINION THERE WAS A MALFUNCTION IN ACFT #4'S XPONDER CAUSING FALSE TCASII RETURNS.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.