Me thinks your professor was an idiot.
The engineering design failed in the opinion of the professor. Yet, there was documentation saying HOW to install something that wasn't followed?
Further - somewhere someone had figured out there was a problem in this area and had written corrective procedures to avoid the problem. That of and by itself can be considered an appropriate engineering response to a problem! Don't forget - engineering is the application of science to real world problems while optimizing the cost of the solution.
There are plenty of engineering disasters to look where design WAS the reason for failure. The classic is the Tacoma Narrows Bridge. Yet even THIS should REALLY be ascribed to a poor understanding of aerodynamics as applied to the bridge structure that was prevalent at the time.
Lastly - aircraft design is really one of the places within the practice of engineering where past errors are studied extensively with lessons learned applied to new efforts. Perhaps better than any OTHER engineering pursuit. The current safety rate of commercial aircraft proves this point.