[gvb]

In the SpaceX feed they were waiting for the second stage to separate and light, and it didn't do either. So first question is why didn't it separate?

T+00:16 - Shortly after liftoff, when the engine graphic first appears, three engines were out. https://youtu.be/-1wcilQ58hI?t=2721

T+00:28 - Sparks are seen in the engine exhaust and some flashes. https://youtu.be/-1wcilQ58hI?t=2733

T+00:40 - A fourth engine is marked out. https://youtu.be/-1wcilQ58hI

T+01:02 - A fifth engine is marked out (just after the announcer says "we're throttled down and throttled back up") https://youtu.be/-1wcilQ58hI?t=2766

T+01:08 - More sparks (streaks) come from the engine https://youtu.be/-1wcilQ58hI?t=2773

T+01:16 - There is a shot of the aft of the rocket and it looks like six engines are out https://youtu.be/-1wcilQ58hI?t=2781

T+01:19 - MaxQ is called https://youtu.be/-1wcilQ58hI?t=2783

My totally uninformed speculation is that the first stage did not achieve the target velocity (and trajectory?) due to the 6(?) engine failures so the first stage continued to burn and the second stage never separated because the separation conditions were not met (velocity/trajectory).

[ChuckMcM]

Pretty solid reasoning. Pretty clear that correct attitude of the spacecraft would be a go/no-go for booster separation.

Wonder if people heard the sonic boom on the ground. If it hit MaxQ and went past it then it would be supersonic at that point.

Presumably they have two flight abort systems (one booster, one ship), a separation, even under non-ideal circumstances, could provide test data. The safety issue would be addressed by setting the self destruct to occur post data collection or imminent danger which ever came first :-). Based on the NOTAMs the FAA sent out they seem to have had a pretty long footprint over the Atlantic for things to go wrong.

Hopefully they will give us a deep dive on what happened!

[svachalek]

You can see the vapor ghosting off it when they call MaxQ which is a visual confirmation. I assume people could hear it on the ground too unless it's too high?