That’s the coldly clinical term the NTSB uses to describe a host of IFR sins eventually leading to wrecks. Most occur on non-precision approaches.

By An Aviation Safety Magazine Staff Report

Even the casual student of why aircraft accidents happen knows that in a large percentage of them, weather is a factor. (It’s about 15 percent.) That’s not to say weather caused the accident, just it was implicated as one link in the chain of events that led to the typical accident. When we think "weather," icing, thunderstorms, low visibility and turbulence come to mind, as well they should.

But the NTSB’s accident files reveal a particular subset of accidents in which pilots operating in flyable if challenging IMC prang perfectly good airplanes into terrain and obstacles for no apparent reason. The agency throws these into a grab bag category it blandly…