Following this tragic accident, I really think we need a rethink regard collision avoidance in the UK.
In relation to fixed wing aircraft, in respect of high wing aircraftm they are very blind in the turn, which is why we teach to lift the wing prior to the turn, although from my experience of conducting renewals quite a few pilots do not. The low wing aircraft on the whole in terms of visibility much better. Bi planes are worse that high wing aircraft.
I can speak for rotary wing pilot's pilot's but I am surethey have limitations, although the Bell 47 must have had the best visibilty of all helicopters ever manufactured.
There are technological fixes to this problem such a TCAS or the ability to see flightradar24 in real time whilst airbourne.
But there are some more low tech fixes that would help improves matters, such as keeping landing lights on all time, ensuring an AFISO is on duty at A/G airfields, establish VRPs for the purpose of departure of departure, and rejoins, listening out on R/T and building the 'big picture' 'SITAW'. Then there are the Human Factors issues of looking out for other aircraft, such as constant angles, makings or colour of aircraft, the the fact that white is not the best colour, but I understand, but I understand the limitations of colours on GRP or carbon fibe aircraft. I should add why would you want to paint the underside of a light aircraft light blue.
Sailplanes (gliders) are another problem, generally white, constant changing height and heading and at times really difficult to see in the turn, but some are on on flightradar24. I am really not sure what the solution is in relation to gliders and it is not helped that they have less ability (energy) for evasive action.