GTS 8000 units with software version 2.21 and earlier (interfaced to a Garmin GX000 Integrated Flight Deck) are affected.
When two Resolution Advisory (RA) aural alerts are triggered in very quick succession, the RA aural alert triggered last may be incorrectly inhibited, causing a conflict between the RA heard and visual RA information displayed on the Instantaneous Vertical Situation Indicator (IVSI).
When responding to an RA, always maneuver as indicated by the IVSI, regardless of what aural alert is heard.
Refer to AC 120-55C for TCAS operational instructions and good operating practices.
This issue is corrected in GTS 8000 software version 2.22.