[roncachamp]

If the aircraft that broke up causing the fleet grounding was built in 1980 and if it did average 250 flight hours per year, then it was at about 7000 flight hours, not 25,000 flight hours.

[Yo-Yo]

I assume you read my post #85. The accident aircraft had "accumulated 5,700 flight hours ... or 11,000 “equivalent spectrum hours”".

Also, the longeron that failed was 0.039 inch thick at the point where it failed, where the spec called for 0.10 inch plus or minus 0.01 inch. That's only 40% of the specified thickness.

The part did not meet it's manufacturing tolerance (thus was defective) and did not meet it's design lifetime (quoted as 31,000 hours.)

It was 40% of the thickness it should have been, and lasted 40% as long as it should have.