I have a question that is relevant to this thread, so thought best to ask here.
Sitting watching a game at Richmond Rugby Club before Christmas, there were aircraft on approach to land at LHR. I noticed that some had their landing lights on, some didn't. I guess this was about 16:00. It was getting dark, if not completely dark (to use a technical phrase!).
My question is: if the company SOPs do not state that the landing lights must always be switched on below FL10 (which must have been the case for the aircraft I saw without landing lights, assuming the pilots were following SOPs), is the decision to use them on approach at the commander's discretion? If so, how do you decide when dark is dark enough?