What in the purple hell was that???

[Stephanie Belser]

Does anyone have any idea what would be bombing down the middle of Long island Sound at FL500 and approximately Mach 4.7 this afternoon?



Something had to be there for ADS to track it.

[Ralph Jones]

That's too much for an SR-71. Decaying space junk, maybe?

[Stephanie Belser]

Space junk usually isn't heading to the southwest, climbing, and running a transponder.

[Tom Tyson]

But it seems to be going in the wrong direction for “Normal” space junk.

[Stephanie Belser]

Winds at FL 530 are from the SW at 70kts, so that thing was moving through the air at 2,800+kts.

[Ray Tackett]

When TW800 exploded in the same area, there was a missile theory with a realistic-looking radar track. The unlabeled, seemingly primary return, was acually an interference pattern from some combination of multiple radars and echoes. I believe it was Bill English (NTSB) who posted a detailed explanation here once it had been solved.

That is an area with a lot of radar coverage and a lot of aircraft, so I could believe another interference pattern. Did that track originate anywhere? Did it end anywhere? Did it even enter ane leave the image area, or did it just appear? Any reports of a sonic boom? Any real object going that fast at that altitude would produce one.

[Scott Dyer HPN/NY]

Ray, it's ADS-B only, so no live radar with echoes and all. Stephanie, I got a speed mod...it was a bad hit and scrambled my hex code.

[Ray Tackett]

Ray, it's ADS-B only, so no live radar with echoes and all. Stephanie, I got a speed mod...it was a bad hit and scrambled my hex code.

Yeahbut ... It's still a LOT of transmitters in one area, all operating at radar frequencies. The exact type of transmission, 1940s radar, Mode C transponder squawk, or ADS-B doesn't matter. The basic physics of wave interference still apply. I think the absence of a sonic boom is pretty strong evidence.

[Russell Holton]

Someone remind me how ADS-B works? Isn't speed self-reported and comes from the on-board GPS receiver? Of course, I wouldn't rule out a scrambled data packet. All those ADS-B packets flying around, I wouldn't be surprised if two stepped on each other.

The real question is what was the "hits" just before and after that screen shot?

[B.Butler]

Someone remind me how ADS-B works? Isn't speed self-reported and comes from the on-board GPS receiver? Of course, I wouldn't rule out a scrambled data packet. All those ADS-B packets flying around, I wouldn't be surprised if two stepped on each other.

The real question is what was the "hits" just before and after that screen shot?

No. Speed is calculated from target displacement. D = RT

[B.Butler]

R = D/T ?

[Russell Holton]

R = D/T ?

But who is calculating it? The aircraft or the ADS-B receiver?

Taking a quick look at the packet format, there is a "Airborne velocities" field.

[B.Butler]

But who is calculating it? The aircraft or the ADS-B receiver?

Taking a quick look at the packet format, there is a "Airborne velocities" field.

The ADS-B transmits a sequence of positions, not speed.

[Scott Dyer HPN/NY]

Yeahbut ... It's still a LOT of transmitters in one area, all operating at radar frequencies. The exact type of transmission, 1940s radar, Mode C transponder squawk, or ADS-B doesn't matter. The basic physics of wave interference still apply. I think the absence of a sonic boom is pretty strong evidence.

Ray -- ADS-B operates at 978 and 1090 MHz. The echoes that are discussed are from primary radar, not DME/Mode C transponders, as I understand it.

[Scott Dyer HPN/NY]

The ADS-B transmits a sequence of positions, not speed.

Bill, I'm reading/understanding that ADS-B data packets include speed as well as position and altitude. https://mode-s.org/decode/adsb/airborne-velocity.html

"ADS-B Out works by broadcasting information about an aircraft's GPS location, altitude, ground speed and other data to ground stations and other aircraft, once per second." https://www.faa.gov/nextgen/equipads...ties/ins_outs/

From: https://www.icao.int/APAC/Meetings/2...B%20Basics.pdf