In my experience most engineers understand verification, namely, ‘Does my system fulfil (meet) it’s requirements’ but there is often difficulty understanding the importance of validation, in this case ‘Is my system right’. In this blog I will attempt to clarify the difference between these two things through some famous failures.
Everyone knows the story. In the cold water of the North Atlantic, when the Titanic hit the iceberg, many rivets failed and whole sheets of the hull became unattached. Here, verification failed; the ship was not built right, compromises were made on the quality.
Hailed as “the car of the future” this car lost Ford $350 million in the late 1950s due to poor validation. The requirements were good and they were verified, but there was insufficient customer demand so the car flopped.
Tacoma Narrows Bridge
See the video here. Here engineers re-used verified requirements from a previous, already built, design; verification was OK, the Tacoma Narrows Bridge was built right, but it was the wrong bridge for the installed environment and the bridge spectacularly collapsed in 42mph winds. Failure to validate the requirements was the mistake here.
Here the operating voltage of the thermostatic switches for the oxygen tank heaters was changed; this change in requirement was not detected during verification. The resulting “pretty large bang” caused the mission to be aborted.
This blog has hopefully gone some way to demystifying validation through the use of some examples that show that even when a system is built correctly (meets it’s requirements) then the system may not be right. Thus poor validation may lead to dister!
Where verification of requirements and verification of the system against it’s requirements are important, it’s also important to validate the requirements and validate the the system to assure a quality system!