United Airlines Rolling Out New Pet Carrier Tags After Dog's Death

United Airlines says its flight attendant did not hear or understand the woman whose dog was placed in an overhead bin -- but it's taking new steps to avoid a repeat disaster ... TMZ has learned.

United tells us by April it will start issuing "bright colored bag tags to customers traveling with in-cabin pets." The idea is the visual tag on a pet carrier will help flight attendants know for sure when someone's traveling with an animal.

The airline says that's exactly what didn't happen in the case of Catalina Robledo and her French bulldog, Kokito. United says after speaking to passengers and crew members, it believes Catalina did tell the flight attendant she had a dog in her tote bag carrier -- but the flight attendant "did not hear or understand [Catalina]."