"Engineers were never able to determine the exact cause of those earlier problems..."
That's an understatement.
"... and many favored changing a launch rule to permit a flight if three of the four sensors were working properly."
I go back and forth on this one. Usually the reason for a rule set in place years ago is a good one. USUALLY. Sometimes it can be redundancy, or something that had to do more with bureaucracy than anything else.
However, with a lack of evidence of such a situation, we have to assume there was infact a good reason. In which case, changing the rule just seems reckless.
"But in a bit of a surprise, shuttle program manager Wayne Hale today decided to stick with the four-of-four ECO sensor launch rule..."
This persistence in sticking with the rule makes me believe that there's something more to this rule that we really don't know about.
Then again, this could just be the stubborn nature of a manager.
"The launch team left open the possibility of revisiting the three-of-four rationale if a failure is actually observed."
So... basically there saying were sure we need this rule, until it causes a problem... Then we can modify the rule at our own convenience?
Now that's bad safety, not to mention bad engineering.
"We have a great deal of confidence we're not going to see any issues..."
Just like you did the other bagillion other times?
The Trouble With Sensors V
The Trouble With Sensors IV
The Trouble With Sensors III
The Trouble With Sensors II
The Trouble With Sensors I