United Flight with a T suffix

Can anyone tell me what the T at the end of a Airline and flight number means? For example, today, United Flight 891T flies from JFK to LAX.

Herkyman

Good question. Typically, UAL891 is LAX to Tokyo. My original thought was a codeshare, or even charter, but for the charter, the flight number would be wrong (?).

If JFK-LAX leaves late and is still in the air when LAX-NRT takes off, it could cause some confusion, so airlines will sometimes append a letter to the end of the flight number (T and K are common).