I'm trying to find the L1011 situation referred to here...and I can't. However, as I recall, a mechanic failed to properly install the O-rings in all three engines...causing the engines to fail.
Ooo...I found this
"Every evening the plane was checked over by mechanics. In the check, they would remove a magnetic plug from the engine and look to see how many metal particles were sticking to the magnet. This is a good way to check on the amount of wear, indicating when the oil should be changed or the engine overhauled. After the plug is removed, there is a hole that allows oil to leak out, so of course it has to be filled with a new plug, and the plug itself sealed with a rubber "O-ring."
Well, the plane was checked, serviced, and returned to duty. Unfortunately, they didn't put O-rings on the plugs, so they leaked. All three of them. This despite the fact that two different mechanics serviced the three engines, despite the fact that after servicing, they turned on each engine to check for leaks. Why weren't the O-rings put in place? The mechanics had even signed a check-list that they had installed the O-rings.
The problem was, for the many years they had been working at the job, they had never ever installed O-rings. Their supervisor always did it for them. The supervisor tried to be helpful. For years, he would get the plugs and the O-rings from the warehouse, put the O-rings on the plugs, and then store the assembled parts in his desk drawer. This made it easier for the mechanics to do their job, so easy in fact, that these mechanics had never ever had to get the parts themselves from the warehouse or install the rings on the plugs."