This sounds far fetched but did happen.
A friend of mine was a 212 co-pilot. One foggy day he was asked to do a ground run for main motor tracking. Following a successful ground track the engineer asked if they could check it in the hover. That went well & the engineer then asked if he could pull some power. Being a helpful sort of chap my friend obliged. The next thing he knew he had lost sight of the ground.
He went down in history as the first pilot in the company to divert from a ground run!
