Engine Misfire at Altitude.

[mshac]

That's good info about UAT above 18k, but if you're that high anyway, you'll be IFR and under normal traffic separation rules, so I wouldn't be too concerned about not seeing 1090 equipped traffic. Many of us use a portable 1090/978 in unit for weather and traffic to display on our tablets, so at least there's that. I'm not familiar with "basic 1090" - I guess that would be a 1090 equipped aircraft without ADS-B? I wouldn't imagine there would be many of those around.

Fun fact - Class A airspace used to be called "Positive Control" airspace (IIRC), and it started at 24k, not 18k. So for the longest time you could fly VFR right up to 23.5k.

[n86121]

That’s right

Basic mode a/c a mode A/c transponder without ads b out.

Mode S can be selectively interrogated by radar.
Rather than just interrogating everything in sight.
But even mode S doesn’t have ads b out.

Only mode S extended squitter (ES) replaces w ads vector info.

What I’m hearing is once you get away from major metropolitan airspace,
a lot of smaller aircraft not equipping w ads b

If they don’t go into the airspace that requires it,
they don’t have to get it.

It’s a mixed blessing. Great where everyone has it,
but no guarantee one is seeing everyone else.

[mshac]

My old Bonanza had some sort of a "Transponder sniffer" traffic device that was probably from the 1980's - whenever it sensed a transponder nearby a red light flashed and there was a warning tone. It had HI-LOW sensitivity, you kept it on HI, then if you got an alert switched it to LOW. If you got another alert, you knew the other plane was closing on you. It sure did keep your head on swivel when it alerted - Good times...