Inspecting an airplane using best industry practices, applied by consensious and trained mechanics, with help and guidance by our regulator authorities, one is still left with rumsfeldian unknowns; Something still might be wrong.
When something does go wrong, often the mechanic is blamed because "he should have caught it". Before this claim can be made one has to determine what the mechanic knew and did not know and why. It could be:
- He might have known but ignored the condition (known-known).
- He might have known that a condition could or did exist (corrosion for example) but its severity or signifigance was unknown. (known unknowns)
- He might simply have not known about the condition and therefore it never occured to him that there could be a problem. Example, might be an undisclosed manufacturing defect. ;This is the unk-unk (unknown-unknown). "I never heard of that problem."
unk-unk is a slang engineering term thought to have originated at Lockheed. The problem of "we don't know what we don't know" is a trap anyone doing maintenance can fall into, not grasping the significance (or danger) of an action or inaction. The best defence against unk-unk problems is to follow well established procedures and standards even though "It's always more fun to go off rapidly on your own and invent your very own personal mistakes rather than look up and actually study somebody else's stuffy reference book."