4) If so, why, if not, why not.
- It's a bit more clutter in the cockpit.
- There's a danger it may give a false sense of security and keep eyes inside the cockpit rather than outside.
- Quite a few aircraft don't have transponder fitted or turned on.
- The perceived risk of a mid-air collision is greater than the US accident statistics show the real risk to be.
This viewpoint is often held by people who have never flown with a transponder based warning system. Conversely, I've never heard a pilot who HAS used one of these sytems say that they are no good. Keep eyes inside the cockpit rather than outside? They most definitely DON'T if used properly, namely incorporated as part of a proper lookout scan. A glance inside at the screen takes less than a second. As soon as this equipment indicates a possible threat the eyes are most definitely outside.
I have good vision (still 6/5) and often spot other aircraft well before my second pilot BUT after using TCAS and TAS (about 8 years now, 4 different aircraft types) my eyes have literally been opened to how many other aircraft can pass close by unseen (even in what would be classed as excellent visibility, the problem being lack of contrast).
Also, unaided lookout simply can't see through that lump of cloud between you and the aircraft that is going to hit you from above and behind, or immediately below and climbing towards you.
Some who firmly believe that the sky is usually clear and their own unaided lookout is perfect might just be the ones who most need TCAS/ TAS help. They might perceive the threat of collision to be less than it is, simply because they aren't seeing how many other aircraft are actually around them.
My type of ops require often VFR to IFR and back to VFR, most of it in class G airspace. Whatever the conditions, almost on every flight I encounter at least one aircraft who fails to comply with the rules of the air, especially with regard to giving way to an aircraft on the right. Assuming that everyone has passed the air law exam, that leaves two possibilities. Firstly, some pilots know the rules and ignore them, or secondly, some do fail to see other conflicting aircraft. I know I might not have seen some of these aircraft so early myself without TCAS to assist me, obviously some I do see perfectly without, or I probably wouldn't still be around writing about it after thirty one years of flying for a living. It's just as possible that I have failed to give way to other aircraft myself because I failed to see them.
The risk IS out there because the human eye is far from infallible, as more experienced pilots come to realise. Yesterday I spotted (quite late / close) a metallic red Jetranger with white registration lettering (I won't post the reg here), flying westbound, south of Bovingdon and north of the LHR zone yesterday, coming in from my left. That aircraft flew a steady course and passed immediately in front of my aircraft at the same altitude, so my right of way. I maintained course as long as was safe then slowed rapidly to let him past; it seemed he hadn't seen me at all but I had seen him, so had Heathrow Special controller. However, he was one of those not transponding at all and perhaps not talking to someone who might have given him traffic info on my aircraft.
An ex-colleague of mine has suffered mid air collisions twice, both times in helicopters and both times with two pilots on board. Once from above and behind, an aircraft descended onto him, inside regulated airspace. Another time another helicopter hit him from below. A good lookout on his part wasn't good enough on either occasion, because the other aircraft were both out of his field of view. He has developed an exceptionally good lookout (!) but is also very enthusiastic about the benefits of TCAS, which also works when a mere unaided lookout cannot.