Just curious what the highest flight was that my pi was logging. Found this interesting test flight.
Currently at 47,000 feet.
U2s get above Class A FL600.
I suspect the shuttle could have been seen a long way out.
A G450 is supposed to to FL450 but I am sure they would test higher.
gulfstream.com/aircraft/gulfstream-g450
The G650 cruise at FL510 (all of the G6xx and G5xx can do this)
gulfstream.com/aircraft/gulfstream-g650er
My highest was about 67,000. HIBAL doing 7 knots to the SW. The only U-2s I’ve seen were at about 1800 on approach back to Beale AFB
I got I think a gulfstream at 51,000 one time. Also got a citation mustang at 45,000 once, which I found interesting since the service ceiling is supposed to be 41,000 I think.
This was my first time looking for highest flight. I spent all of 5 minutes looking. 
I was more interested in the squarish flight path around the country and figured it must have been a test flight. The FA information on it seems to bear that out. Previous flights are also interesting and different.
An almost 7 hour flight is a long one. I know they probably have a glass cockpit and nice autopilot.
At least they have a toilet, I hope.
Interesting that you should mention the U2. On Tuesday I noticed a spike in my VRS receiver range-plot nearly 400 NM out. I’m in central Oregon and the spike was near San Francisco. I ran a report in VRS for Tuesday’s AC and scanned it for the lowest reported latitude. When I located the row on the report the thing that jumped out at me was the 60000 ft altitude! HeyWhatsThat.com shows that even at 60000 ft I’d be lucky to see much beyond 150 NM to the south. Apparently the Force was strong with this one. Also possibly it was tropospheric ducting. 
The lowest flight I’ve seen (other than the zeroes, which I assume are just no data) is 525 feet. A quick google search shows the airport to be at 542 feet. The plane was at the airport at the time. Most seem to disappear just before touchdown. I almost, but not quite, have direct line of sight to the airport.
I get NYPD flying past at 100AGL. I see plenty flying the Hudson at this altitide.
I have seen some in the negatives. Transponders use 29.92/101.3 or pressure altitude.
When conditions are right, I can see stuff on the ground at EWR, JFK and LGA.
Are you suggesting that transponders use a non-calibrated (or, actually, non-tared) altitude in contrast to the cockpit altimeter?
Transponders report pressure altitude; calibrated, but not adjusted for local conditions. SSR adjusts for local conditions.
(amongst other things, that altitude is used for TCAS so you really do want everyone using the same setting…)
So yes?
Transponders are calibrated. They must be checked every two years, if I recall correctly.
They all use 29.92"/101.3hpa because they need a common reference point. (like using 29.92" in the flight levels).
As Obj stated, the SSR systems have pressure information to correct to the actual altitude on “Radar screens”.
The NYPD regularly flies over my house at 100ft AGL. I also get many aircraft going up and down the Hudson river(about 150M/450ft away) at 300-1200ft .
This thread made me go look at my recent reports and I see a Cesna Citation CJ3 went pretty much directly over me at 45,000 a few minutes ago.
One (Cessna Citation X) just flew over toward Houston with a peak speed of about 639 kt. This website shows winds aloft (not exactly at that level). Nice tail wind.
Speaking of wind, what’s a good resource to find wind velocity at different flight levels?
My highest was a WB-57 at 56k. It was Mode-S only altitude, but no position, track or groundspeed.
Just checking my data for the past week, my highest ADSB is about 58,000 ft. Highest MLAT is about 105,000 ft. That got me wondering if weather balloons transmit ADSB signals. Looking closer at the data, though, there seems to be a bug somewhere. Look at the negative altitudes.
A0E5DF 2016/05/05 00:20:18.862 2016/05/05 00:20:18.862 29.7923,-98.6743,36025
A0E5DF 2016/05/05 00:20:22.119 2016/05/05 00:20:22.119 29.7955,-98.6815,35337
A0E5DF 2016/05/05 00:20:22.146 2016/05/05 00:20:22.146 29.7955,-98.6812,35125
A0E5DF 2016/05/05 00:20:32.445 2016/05/05 00:20:32.445 29.8004,-98.6942,34784
A0E5DF 2016/05/05 00:20:33.030 2016/05/05 00:20:33.030 29.801,-98.6975,34911
A0E5DF 2016/05/05 00:20:41.972 2016/05/05 00:20:41.972 29.8037,-98.7074,35110
A0E5DF 2016/05/05 00:20:42.298 2016/05/05 00:20:42.298 29.8057,-98.7132,35422
A0E5DF 2016/05/05 00:20:47.126 2016/05/05 00:20:47.126 29.809,-98.722,35402
A0E5DF 2016/05/05 00:21:45.678 2016/05/05 00:21:45.678 29.8131,-98.8196,104959
A0E5DF 2016/05/05 00:22:02.914 2016/05/05 00:22:02.914 29.8291,-98.8372,61467
A0E5DF 2016/05/05 00:22:05.789 2016/05/05 00:22:05.789 29.8342,-98.8368,55294
A0E5DF 2016/05/05 00:22:06.983 2016/05/05 00:22:06.983 29.8399,-98.8405,45172
A0E5DF 2016/05/05 00:22:08.824 2016/05/05 00:22:08.824 29.8446,-98.8426,37522
A0E5DF 2016/05/05 00:22:16.150 2016/05/05 00:22:16.150 29.8521,-98.846,21962
A0E5DF 2016/05/05 00:22:18.218 2016/05/05 00:22:18.218 29.855,-98.8473,15942
A0E5DF 2016/05/05 00:22:22.779 2016/05/05 00:22:22.779 29.8614,-98.8548,166
A0E5DF 2016/05/05 00:22:24.297 2016/05/05 00:22:24.297 29.8611,-98.8556,636
A0E5DF 2016/05/05 00:22:34.906 2016/05/05 00:22:34.906 29.8747,-98.859,-31592
A0E5DF 2016/05/05 00:22:49.189 2016/05/05 00:22:49.189 29.8814,-98.917,-33788
A0E5DF 2016/05/05 00:22:49.258 2016/05/05 00:22:49.258 29.8744,-98.9182,-34168
A0E5DF 2016/05/05 00:22:52.047 2016/05/05 00:22:52.047 29.8712,-98.9204,-39734
A0E5DF 2016/05/05 00:22:58.133 2016/05/05 00:22:58.133 29.8698,-98.9206,-47751
A0E5DF 2016/05/05 00:22:58.141 2016/05/05 00:22:58.141 29.8679,-98.9233,-45857
A0E5DF 2016/05/05 00:23:03.393 2016/05/05 00:23:03.393 29.8664,-98.9289,-54712
A0E5DF 2016/05/05 00:23:06.168 2016/05/05 00:23:06.168 29.8651,-98.9315,-56095
A0E5DF 2016/05/05 00:23:08.727 2016/05/05 00:23:08.727 29.8646,-98.9373,-57590
A0E5DF 2016/05/05 00:23:12.760 2016/05/05 00:23:12.760 29.882,-98.9769,-53130
A0E5DF 2016/05/05 00:23:12.800 2016/05/05 00:23:12.800 29.8862,-98.978,-52332
A0E5DF 2016/05/05 00:23:20.793 2016/05/05 00:23:20.793 29.8797,-98.9977,-61743
A0E5DF 2016/05/05 00:23:21.517 2016/05/05 00:23:21.517 29.8747,-99.0081,-64829
A0E5DF 2016/05/05 00:23:26.760 2016/05/05 00:23:26.760 29.8717,-99.0266,-75046
A0E5DF 2016/05/05 00:23:30.141 2016/05/05 00:23:30.141 29.8709,-99.0319,-76644
A0E5DF 2016/05/05 00:23:41.768 2016/05/05 00:23:41.768 29.8688,-99.0561,-89902
Looking up the ICAO code, I get this information on the vehicle.
Maybe it’s not a bug but an artifact of a mirage or something similar. Any other speculations?
Mlat calculation of altitude when there is no transponder altitude available (eg no SSR is interrogating it) is very inaccurate, you shouldn’t trust mlat altitudes much at all.
(it is basically because changes in altitude produce very little change in relative message arrival time, as the receivers are usually close to the horizon relative to the aircraft)
True, which is why I keep that data separate. But in this case, it is way off, not just inaccurate! Maximum distance horizontally from my station in this case was about 100 miles. Difference between maximum and minimum altitudes is about 37 miles. I wouldn’t expect an error in altitude to be many miles off.
Well, the solver code is on github if you want to improve it… You will find that the unstable regions in the solution space are very dependent on the exact receiver geometry and what you choose for your initial guess at the solution.