Two factors probably caused it: 1) It is very hard to visually judge distance to the water when flying over it... Depth perception is affected,; 2) According to what I was told, a NOTAM (notice to airmen) had been issued advising that the glide slope indicator on runway 28L was down. These factors would put the pilot at extreme disadvantage when trying to land at SFO. It would be even worse in a declared emergency when the pilot has other extreme factors with which to deal...
“the glide slope indicator on runway 28L was down”
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That certainly did not help his situation, but unless that runway is critically short, he should have been well past the threshold at touchdown. I guess in a plane that size, however, the runway that the pilot sees is quite far from where the wheels are.
Anyway, it is all over but the shouting, and we can speculate all day long. We just need to wait till the official ruling.
I was not aware of a declared emergency.