Originally Posted by
Wombelero
My main question was why they were active in the middle of the flight at 30'000ft cruising altitude? ANd not just for some minutes. Or did the pilots some routine checks and forgot to turn them off?
My guess is that you're referring to the wing lights, which illuminate the leading edges so that icing phenomena may be ascertained.
And yes, we may forget to turn a light on or off (usually because our attention gets diverted by something else) but it doesn't happen often. The selection/de-selection of lights is procedurally dictated.