It doesn't fire all three engines down to the deck. The landing burn starts with one engine (in order to have more control authority when the two outboard engin

It doesn't fire all three engines down to the deck. The landing burn starts with one engine (in order to have more control authority when the two outboard engines start up), then two more engines get lit, then they shut down shortly before the actual landing (reducing the TWR makes the landing a bit easier).