From Tom Podolec with CTV News:
"
FAA investigating; @AirCanada#AC781 from Montreal landed in San Francisco (Oct 22) after failing to acknowledge 6 go-around requests by ATC"
"Air Canada #AC781 was cleared to land runway 28R by San Francisco ATC prior to go-around requests."
"Air Canada #AC781 did not acknowledge an additional 3 calls by ATC before answering "there's a problem with the radio here"."
"Air Canada #AC781 landed without incident. Go-around request was made due to possible aircraft on the runway."