As Matt Levine says, everything is securities fraud. Boeing defrauded its shareholders (and its public company customers) by saying that it was building safe planes. Even beyond that, the law guarantees protection for whistleblowers within these companies.* These hypothetical engineers would have absolutely been protected.
* If you work for a public company, you've almost certainly had a training about its ethics hotline with information about your protection from retaliation.
* If you work for a public company, you've almost certainly had a training about its ethics hotline with information about your protection from retaliation.