Stress and Aircrew
Performance: A Team-Level
Barbara G. Kanki
NASA--Ames Research Center
There are three kinds of problems you can have with your car: (1) those that will kill you; (2) those that will leave you stranded; and (3) those that will cost you more money if you let them go too long.
Shimmies and shakes--problems that have to do with the suspension and steering of your car--all come under category one. So we're going to look at them in some detail.
The steering pieces--ball joints, center links, idler arms, pitman arms, drag links, tie-rod ends, and so forth--literally hold the front wheels to the rest of the car. If any one of these things breaks, you're in serious trouble. . . . You might say, "well there's nothing I can do about it. If they're going to break, they're going to break." Wrong! If you know what to look for, you can heed early warning signals.
A funny thing happens. People never know when their car is handling badly, because all the things that wear out generally wear out slowly, or incrementally, as the mathematicians say. Everyday, the car gets a little worse--the ball joints get a little looser, the tie-rod ends get a little sloppier, your tires get a little squarer, and all kinds of things happen to make the car handle worse. Except you don't notice because the changes are so small that you adapt to them.
-- Magliozzi & Magliozzi ( 1991, pp. 15-17)
Complex operations, like automobiles, are made up of many interlocking parts, and the way in which the parts work together vary according to the design and condition of the system of parts as well as the design and condition of its constituent parts. Furthermore, as the Magliozzi brothers advise here, a system of parts may wear down imperceptibly because changes due to wear and tear (e.g., stress effects over time) are small, and people adapt to them. However,