Aerospace software engineer here. :-)

I feel perfectly content to deem my work as "engineering". I can understand why someone quickly whipping up a small web application (which is not to imply that all web applications are quickly whipped up, nor that all web applications are small) might reasonably feel that their work is not engineering.

So since I've also done quick little web applications, what do I think the difference is?

The aerospace work includes precise operational requirements. It includes formal verification tests which demonstrate that the requirements are met. Code is reviewed; documents are reviewed; reviews are reviewed (not joking, though typically only a sampling subset). Code is subject to formal coding standards; code repositories are subject to formal standards; tools for testing software are subject for formal standards (and documented/reviewed/etc. in their own right). Software that goes onto aircraft is tested in simulations; tested in limited on-ground hardware scenarios; tested in extensive on-ground hardware scenarios; tested on board flying aircraft. The entire process (and the following of process) is reviewed. The end product is signed off on, and, for example, in the case of U.S. commercial aerospace, certified by FAA representatives.

Sounds nothing at all like developing web applications!

Or does it?

A consumer-facing startup web application might have little or no requirements. Testing may be ad hoc. Nothing is reviewed. Coding standards don't exist. Does the software seem to do what is intended? Ship it!

But what about web applications for banking? I've never worked in banking, but I suspect the requirements are fairly robust. (And if in fact they are not, they easily could be.) I suspect that tests are comprehensives, traced back to the requirements. (And if in fact they are not, they easily could be.) I suspect that the software goes through several rounds of testing, that code is reviewed, that coding standards are adhered to. Maybe not to the same level as aerospace, but probably pretty solid.

So what?

Is financial software engineered? I would imagine so. Maybe not as strictly as aerospace -- or maybe stricter! I honestly don't know. But I can easily imagine comparable scenarios.

So if we can engineer financial software, can we not engineer productivity software? We sure could! How about social media software? You bet! Even games? Why not?

I think that all software could be engineered. But in fact it probably shouldn't be. If you want to make a change on software on an aircraft, it might be five minutes editing code in Emacs, surrounded by a year of paperwork and process. That'd be ridiculous for an iPhone game. It'd probably be excessive for a financial application, but maybe some measure of that would be appropriate.

Perhaps there is (or should be) a spectrum of software engineering. At one end, we take extreme measures to ensure quality and process, because (literally) lives depend on it. At the other end, we can hack out whatever we want and it doesn't matter. Most software lies somewhere in between. Maybe some of it should consider moving more toward one end or the other. :-)

[Incidentally, it's common to repeat the phrase, "never roll your own cryptography software". I think it would be totally fair to say "never roll your own flight control software" too. But the people actually writing flight control software aren't necessarily top-tier 0.000000001% brilliant developers. They are, though, surrounded by sufficient process and review that their work is nearly guaranteed to be solid by the time it takes to the air. We could probably do something similar with cryptography software, if there were a model in place (and, I reckon, funding in place) for all of the surrounding infrastructure to engineer it properly.]