Yes but that was 65 years ago and the context is completely different. Planes crashed all the time back then and our safety culture and technology has changed massively. These steam locomotives[0], that look like they were built by a farmer, were ~10 years old at the time. Comet was incredibly futuristic space age technology. But with no 3D CAD or FEA simulations. No X-ray or ultrasound metallurgy. Crack propagation wasn't understood. Also, there was no CRM, no safety gadgets like stick pushers/shakers. Most pilots and airline management were WW2 ex military and a couple of planes a year is nothing compared to the 4-5 they would lose in a typical bombing sortie. I think there was an attitude of it being regrettable, but just part of life. [0] http://www.railgiants.org/union-pacific-big-boy-back-head.ht...

> These steam locomotives[0], that look like they were built by a farmer

This is a little derogatory, considering the mechanical wonder a steam locomotive was back then and still is today.

What are you talking about?

1) is "built by farmers" supposed to be derogatory, because farmers are often very mechanically inclined and make the best of what they have.

2) Steam engines are very capable, complex beasts. The big boy that you linked to is one of the largest and more complex one's ever built. Diesel engines wouldn't pack this much power in a single unit for multiple decades to come.

2a) you do realize that basically every electrical power plant sans hydro and photovoltaic are basically steam (turbine) engines and these work horses of old sharer large amounts of experience to the power plants of today?

3) The safety culture of the railways has always been important, almost as much as it is for air travel. (Yes, there have been some high profile accidents recently, but comparing fatalities to total trips is still favourable.)

It appears to me you saw a picture of something that didn't look "modern" and thought that it was primitive. It also appears that you thought primitive means simple. Those are never good assumptions.

>Crack propagation wasn't understood

It was well enough understood. Square openings leading to stress risers and cracks has been known in ship building since at leas the 1940s.

Yet it was put into planes. So either it wasn't really understood in the context, or no one that knew about it was advising on the design of aircrafts.

The corners on the windows did have a fairly large radius. Just not large enough (hindsight being 20-20). I think they knew about it and thought they had more than enough margin for safety and then never thought twice about it until aircraft started falling out of the sky.

I oversimplified. It was understood in specific academic circles and to an extent by leading designers, but not widely by others. The cracks actually started at a hatch on the bottom of the plane which was added to the design without going through the full engineering design QA process.

Then it wasn't well enough understood...

Until it was cheap enough to manufacture with, aluminum hadn't been used in large structural components and the crack formation in aluminum is very different from steel.

With steel, if you add a large enough safety margin it will essentially never fail due to repeat stress cycles. With aluminum it doesn't matter how strong you design it, eventually cracks will form and it will fail.

ship don't go trough a thermal and pressurization cycle at every trip however.

it wasn't square window per se as much as metal fatigue