Today, south of the Isle of Wight, 1600ft, cloudbase 1800ft, got very close to a yellow plane, possibly a Robin.
Luckily he had Mode C so I saw him on my TAS605 (TCAS1). Looking hard, not visual, so when he was at 1nm I pulled up hard and climbed by 500ft and as he passed right under and then upon descending back I spotted him. I doubt he ever saw me. He was hidden by cloud which was sticking out below the general cloudbase.
Had this happened a little later in the flight I would have got busted for busting the 2000ft Solent CAS by 100ft. Another factor was a temporary prohibited area up to 1200ft on the route.
You might say this happens all the time and it probably does because half UK traffic is flying non-TXP now due to this but “not knowing” is okay in this department 
I never go against my TCAS but avoiding laterally might be better.
Good you avoided it without incident.
Vertical avoidance is always better; the position on TCAS is a lot less accurate than Mode C (if available) unless the aircraft transmits its position via mode S.
One thing to keep in mind is that the instinct when taking avoiding action is banking and pulling up; so in general being contrarian and descending can be a good idea, terrain and airspace permitting of course.
The proximity described with another light aircraft happens to me about every other flight. I usually steer around them but last resort would be steep roll, let the nose drop. That loses altitude really fast. ADS-B has so far made that unnecessary and I can fly around them pretty accurately with or without seeing them visually.
Agreed, though a straight descent is a lot more likely any passenger vomit One would need to do a descending turn.
If I can be the devils advocate. What would the effect have been if the Robin also had TAS and saw you on his display and took the same avoiding action?
ACAS on large aircraft co-ordinate the escape manoeuvre via Mode S so one aircraft climbs and the other descends (assuming pilots follow the commands). With no coordination for TAS-equipped aircraft, the AFMS instructions we had to write in on CAA/EASA mods required the pilot to visually acquire the target aircraft before committing to any avoiding action.
Doesn’t that mean taking no action in IMC and just flying straight ahead, fingers crossed, hoping to not die even if TCAS is showing you on a perfect head-on?
Either the other guy did not see you (perhaps most likely) in which case any avoidance is fine, or he did see you, and assuming he has some IQ he might do standard head-on avoidance which is a right turn, so you could do the same. But a) a lot of pilots don’t know this b) a lot of near misses are not obviously head-on, so anything is possible.
This leads to doing some maneuver which is calculated to be more aggressive than the other guy is believed to be capable of, which is what I did today. However, I did that at Zell am See LOWZ a while ago and climbed (post departure, a stupid departure route required) at 1000fpm only to find the other guy, right under me, was also doing 1000fpm. Eventually he went off somewhere (he wasn’t LOWZ traffic; he was just mucking about near it).
There is no good solution.
Peter wrote:
he might do standard head-on avoidance which is a right turn, so you could do the same. But a) a lot of pilots don’t know this
If that’s the case, then said pilots have not received proper training. It’s the standard avoidance maneuver and taught at PPL level.
That said, it’s rarely a straight head-on situation, so you have to make a quick decision what will likely work. ADS-B makes all that pretty easy, close encounters of that kind are more or less standard in SoCal airspace and you just avoid. If it really looks like the situation might get weird, you can always call the other airplane, ADS-B displays the callsign.
It was very close, as I thought at the time.
Very slick software!
Watching that movie shows an important aspect of mid-airs: a constant angle. A target on a real collision course is stationary in the field of view, so isn’t visible.
So what is the lesson there? Not fly under a low cloudbase; fly above the cloud, or inside it.
