[Catfish]

I read about this when it happened, i take it this vid sums it up well.
Thorough going through what most probably happened by the narrator. Nice that some lhave the energy and determination to let those birds fly, on the other hand it seems like a critical lack of maintenance and security procedures, and training. The pilot was experienced, but maybe "a bit too much".

Engines 4 and 3 had had issues before, from corroded intermittent or failing magnetoes to ignition, to jury-rigged contacts and mass fails, and wrong spark plug gaps, and wrong contact breaker gaps as well. Plugs were also sooty and some of them seem to have not worked at all. Engine 3 would not start, then engine 4, moisture was removed with nitrogen spray via a tube installed for that purpose, then finally engines started in order of 3-4- and the rest. (I think the main generator or hydraulics supply is in engine 3, so it was mandatory to get this going first(?))
Some say they did a run-up test of the engines, others say they did not and the start was rushed.

The pilot had a problem with engine 4 a good minute after taking off, and the pilot probably expected this, knowing of the magneto problems of #4, but he was wrong. Engine 4 was "running rough" but it turned. Pilot informed the tower that they were going back, but declared no emergency.

He turned off engine 4 and feathered it - but really it was engine #3 which was in trouble and was losing more and more power due to predetonation and backfiring already at the start. So when this engine #3 now lost revs and power they finally had two engines off on the right side, and had to fly at an angle to make up for the sideslip, inducing very much drag and thus losing more speed and altitude.
It seems, that at no time was the plane higher than 400 feet, above the ground.

In the video the narrator says he should have left engine #4 on, a bit less performance is better than none. But i have no idea whether this was an option at this time.

The pilot then lowered the landing gear too early, resulting in even more drag and less speed long before the runway. Despite this they were almost aligned to and near the runway when speed went so low that they touched the ground some 300 feet before the strip, shearing off the runway's landing lights, the right gear touching down, and the plane veering off to the right - both left engines running at full speed and still adding energy, pulling the plane further to the right (If this is true, I have no idea why both left engines were not throttled down at this point), where it left the runway, ran over grass and a taxiing strip, and finally crashed into a building and burned.

Survivors said the passengers had not been informed how to leave the plane in an emergency, how to quickly unbuckle their seat belts and how those hatch locks worked. One of the passengers in the rear knew how to do it, without him there would probably been no survivors.

The narrator presses on the importance of proper training, it seems the co-pilot did not know enough of how to fly a B17, or help the pilot with trimming in emergencies, or acknowledging thorough shut off procedures (propellers 3 and 4 were not turning at impact, but 3 was also not feathered)

Adding to the later problems, primarily lacking engine maintenance seems to have been the core problem. Not declaring an emergency led to a delayed arrival of fire fighters and rescue personnell.