Power to vital components lost at 4 mins before landing points to something quite significant occurring that seems to go against so much of the commentary around the resilience of electrical systems in the 737.
It’s a very telling bit of information. Power to the recorders will be drawn from a couple of the aircraft buses (not the same one for each recorder), and it will stop any recording if that bus is unpowered. The buses themselves are powered by the engine driven generators, and the APU. The aircraft battery will be on a separate and very limited system, and powers only what is considered absolutely necessary, and recorders aren’t. I haven’t looked at it to any great extent, but apparently aircraft built after 2010 have to adhere to a new requirement for a form of battery backup to the FDR, but this aircraft was built before then, and in any event, it’s just as likely to have been grandfathered out. This isn’t a simple panacea though, as it’s all well and good having a recorder that has power…you then have to ensure power to all of the systems that it’s trying to record.
The implication though, is that at that -4 minute mark, both engine driven generators went off-line, and the most likely cause of that is for the engines to have been shut down. But, the aircraft was, at that point, quite some distance from its ultimate touch down point, and headed in the wrong direction. It simply would not have had sufficient energy to get to its final landing position, at the speed it was going, from that point.
Both engines would not have failed together. Whether they self shut down, or it was pilot action, there will be some level of data recording from the initiation of the event up to the loss of power. That should be enough to say whether both engines were involved in the strike(s).
In many ways the flying is separate from anything to do with the engines. At a guess, it would take around 2,000’ to do the turn he needed to do, clean. That basically means that you really can’t go below 2,000’ before starting the turn, even if you know that it will roll you out well after the threshold. If you don’t turn at the height, you’ll reach the ground before finishing the turn. I doubt that he had any reason to expect the overrun contained a solid obstacle and may well have figured that ending in the overrun wasn’t going to be too bad an outcome.
