B737 Undifferentiated or Other Model
Flight Crew Total 1456; Flight Crew Type 785
Human-Machine Interface
Aircraft Equipment Problem Less Severe
Flight Crew FLC complied w / Automation / Advisory; General Maintenance Action
Aircraft
Two TCAS Resolution Advisories (RA) were received while at cruise altitude with no traffic observed or reported in the vicinity. The first incident occurred at [an] altitude [of] FL370. The TCAS system momentarily displayed amber traffic advisory symbols with the 'Traffic; Traffic' aural warning; followed immediately by the RA directing a climb. The RA continued until the aircraft was flown to approximately FL374. Prior to the event; the TCAS system was not displaying traffic in the vicinity; nor was traffic observed. The RA was immediately reported to ATC. ATC advised that there was no traffic in the immediate vicinity. The second incident occurred [an hour later] while at FL390. Once again there was no traffic observed or displayed by TCAS near the aircraft. During this incident the TCAS again displayed traffic symbology and aural warning; followed by the RA directing a descent. The RA guidance remained until the aircraft descended to FL386. The RA was reported to ATC. ATC advised the nearest traffic was 40NM from our position. During both incidents; transponder #2 was in use. Suspecting an equipment malfunction; the #1 transponder was utilized for the remainder of the flight. A logbook entry was made providing the details. Maintenance elected to defer the #2 transponder for the subsequent flight.
A B737 First Officer reported that after two TCAS advisories with no confirmed traffic in the area; they determined it was an equipment malfunction.