Fortunately they were already doing a go-around by the time ATC noticed, a few seconds later would have been a disaster. Their minimum altitude was reported as 18m, which is a bit under a metre above the tail height of a Boeing 787-9.

They do have those alarms, but it was initially reported this plane was too far off course from R28R to trigger them and part of the investigation will be whether they were even operating at the time.

A major contributing factor for this incident was that the second runway, 28L, was closed and lights off at the time of the incident. As a result, the FAA has changed San Francisco landing procedures no longer permitting visual approach when an adjacent parallel runway is closed - https://www.flightglobal.com/news/articles/faa-changes-san-francisco-landing-procedures-after-a-440380/

Airbus A350 vs Boeing 787 has been added as a related post - related requested by oritteropo on that post.

Airbus A350 vs Boeing 787 has been added as a related post - related requested by RFlagg.

Comparing this against the 787 is *related=http://videosift.com/video/Airbus-A350-vs-Boeing-787