You don't know much about aviation, do you?

Aviation is about redundancy. Redundancy is a good use of a pilot's focus. That's why I did both. I didn't blindly trust my calculator to not have bugs (even though I wrote it!), and I didn't blindly trust my hand calculations to be correct.

If they agree, though, it's a good sign that everything is in good order. That's what redundancy is for, to ensure that a problem in one thing does not lead to another problem, like in the Swiss cheese model of accidents.

Redundancy is not a good use of focus for most people (except SREs and the like). The whole point of redundancy is to remove something from focus. I'm guessing you checked everything by hand for the sole purpose of not having to focus on these calculations mid-flight. I'm sure most commercial pilots rely on a larger organization to make these checks for them and their organization probably employs its own system of checks and redundancies at scale. Putting that all on the pilot is not going to give you a sustainable transportation business.

If you're just trying to get off Gilligan's island, that's another thing entirely.

The final authority, and final liability, for the airplane is on the head of the pilots.

A commercial pilot friend has told me that they still check the calculations. When they don't, they get accidents like the Gimli Glider.

It's like saying that putting all of the legal checks on the lawyers is not going to give you a sustainable business. But we all know that's wrong.

What was the outcome of that incident? Fault was found with the Air Canada procedures, training, and manuals, while the Captain and First Officer went on to receive FAI Diplomas for Outstanding Airmanship. What did not happen was mass calls for the individual pilots to write their own calculation software. I'm not sure what point you're trying to make here, as reading about the incident you mentioned only paints a clearer picture that systematic redundancy is the responsibility of the creating and maintaining the system, not of those using it.

Yes, they did, but I think they should have also been censured for their lack of care as well.

When I wrote that calculator, I didn't write it for flight. I wrote it as a general calculator and just used it for flight. I would have used the GNU bc if I didn't write my own.

So it's a bit disingenuous to claim that I am claiming that pilots should write their own.

And pilots are included in those maintaining the system; they're not just using it.

It is the ability to do the calculations that matters, not that you would do so in actual practice. He very explicitly mentioned 'while I was learning'.