"Non-normal" is a Boeing-ism, I believe, for something that is not routine, but not emergency. I think it covers things from cross-bleed starts to engine shutdown and relights.
Abnormal would have covered it. If you get engineers (in the broad sense) to write things, don't expect English.
My favourite other example is making the singular of "vertices" "vertice" in a computer graphics application.
From an ex-engineer (in the broad sense).