For reasons that, at present, we can only speculate about, neither pilot appears to have seen the other aircraft in time to take effective avoiding action.
We were told in an early post that
The Netherlands airforce painted their Pilatus PC-7 basic trainers black a couple of years ago, because research had shown that black aircraft are better visible against a daylight sky than other colours.
For opposite reasons, many species of fish have evolved colouring that is dark on top and loght below. Should aircraft, in particular those that frequently climb and descend in congested airspace, be required to adopt a complementary colour scheme, with light colour on top and dark below? Or even better, large patches of the type of the flourescent colours used on high-visibilty jackets.
I understand that some WW2 fighters had mirrors to give a view into what would otherwise have been blind spots. Why not fit them to modern light and medium aircraft, particularly helicopters, with their ability to move in directions where the pilot cannot easily see?
The mirror is a simple and generally reliable piece of technology, but there are better and relatively cheap alternatives. Modern domestic video cameras are small, light and relatively inexpensive; likewise small colour displays. A trip to the local consumer electronics shop should produce all the bits for a simple installation for five or six hundred pounds, though I suppose a fully certified installation could cost ten times as much - still relatively cheap.