What’s Flying Above Us? | Hacker News Reader

What’s Flying Above Us?

skycircl.es

544 pointszuhayeer164 comments

Hi! I made this.

A few points I wanted to make, specific to the HN context (and a lot of this is in the "nerd mode" donation page at https://skycircl.es/donate-nerd-mode/):

1. This seems like a classic "low effort, high impact" project. It's super easy to detect aircraft flying in circles, in real-time, and post it to twitter. But it turns out to be an entry-point into a "strangely interesting" (according to pg) world of aircraft activity.

The current #1 comment sadly only gets to see general aviation pilots practicing, but my bots have tweeted military aerial refueling, STOL practice in the wilderness, float-planes practicing on rivers and lakes, military drones flying over the desert, planes dropping sterile fruit flies as a way to reduce the fruit fly population, news helicopters following a highway pursuit, U.S. Forest Service AH-1Z Viper attack helicopters fighting fires, helicopters dropping mosquito pesticide, aerial tankers over Manhattan for the president's combat air patrol, FBI surveillance planes registered to front companies, Coast Guard helicopters doing search & rescue, crop dusters, scientists observing sea life over the ocean, planes doing Gorgon Stare-style persistent surveillance over Baltimore, sheriff's helicopters rescuing hikers, power line inspections, pipeline inspections, military aircraft doing surveillance over protestors, stealth jet test flights, a Grumman HU-16 Albatross seaplane that belongs to the USAF over the Mojave desert, a U-2 test flight, and a B-29. That is not even close to a complete list.

2. All the code is open source. See https://gitlab.com/jjwiseman/advisory-circular/ and https://gitlab.com/jjwiseman/whatsoverhead

3. As far as I know, this comment on HN is the first time anyone published any significant detail about the FBI's secret aerial surveillance program: https://news.ycombinator.com/item?id=9508812

Thank you so much for making this. I was constantly checking it to determine what was flying above our house in Minneapolis during the recent civil unrest. I took comfort in at least know what was buzzing us and why it might be doing it.

Thank you for your work! We need MORE information about what our government is doing at all levels, not less.

The FAA uses the term "advisory circular" to share information with pilots and aircraft operators, using "circular" in the way of "bulletin" or "newsletter" [1]

I was really confused at first by your use of the phrase.

I also think it is pretty funny if you didn't intend it. I would have thought what you're doing is better described as a "circular advisory" rather than "advisory circular". Cool project :)

[1] https://www.faa.gov/regulations_policies/advisory_circulars/

Thank you. This is crucial information.

> my bots have tweeted [...] U.S. Forest Service AH-1Z Viper attack helicopters fighting fires

I had to Google that. I'll await a correction from a more knowledgeable HNer, but as far as I can tell the US Forest Service does not have AH-1Z Viper attack helicopters.

I don't care enough to dig deeply into it, but it seems that basically there is a very long line of Bell helicopters called "AH-1", going all the way back to the original AH-1 Cobra in 1965. There have been many variants over the decades, and two of these have been been retrofitted into "FireWatch" helicopters for the US Forest Service, after being retired from military service.

The AH-1Z Viper is a modern attack helicopter, a variant of the SuperCobra, itself based on the AH-1 Cobra. It went into service in 2000, whereas the USFS two FireWatch Cobra's were originally built in 1969 and 1983: https://wildfiretoday.com/2010/06/27/firewatch-cobra-helicop...

Sorry, I keep getting the exact designation confused, you're right, they have two of the AH-1F Cobra variant, not the later AH-1Z Viper version. https://www.youtube.com/watch?v=d_Y6XhQ0774 gives a closeup look at one.

Hi! This may be a really dumb question but why is it limited to certain areas?

I could make a bot that covered the whole world, but it would be a firehose that nobody would bother following.

Interesting project, thanks! But it is also important to mention AdsbExchange as the data source. They have quite a big expenses on AWS to keep it running and unlike FlightRadar24 or similar they doesn't censor any aircraft or take blocking requests by aircraft owners which is reasonable considering this data is public an anyone with sdr-compatible dvb-t dongle can receive them.

That is a very unfortunate name. I don’t think I’d ever click a link called adsbexchange if I didn’t already know what it was.

Yes, ADS-B Exchange is part of the foundation that makes this possible.

Did you ever got contacted by a government agency?

I have a flight tracking app for my phone and see aircraft flying in circles over where I live all the time. Dozens and dozens of times each day.

They're people in small planes practicing.

Also, I live near several military bases. The interesting and loud stuff that I see flying by out my window NEVER shows up on any app. I expect this web site is similarly, deliberately, incomplete.

Everyone that plans on moving somewhere should do 1 of 2 things:

1. Not move there because of flight training schools.

2. Lobby to get the flight training school to practice over unpopulated areas.

Or live close to a prison or other place with restricted area

#2 Doesn't seem feasible for large portions of the world though.

I did some flight lessons in rural Manitoba. You got ~45 minutes of flight training for every hour you paid for.

Then I considered restarting them once I moved to Toronto... you get about 20, 25 min of training for every paid hour - the rest is just getting out of restricted space. If you wanted to head to actual "unpopulated area", I think you'd need to book a 3 hour lesson in order to get any actual training. Completely unfeasible.

And this is in Canada, a famously sparsely populated nation. It feels even less feasible for majority of more densely populated countries.

(basically, by definition, if you only allow flight training in the unpopulated boonies, you'd deny it to a very large super-majority of population. One may view that in positive or negative light, of course)

> If you wanted to head to actual "unpopulated area", I think you'd need to book a 3 hour lesson in order to get any actual training. Completely unfeasible.

Why is this unfeasible?

Unaffordable might be another word. Rental on the plane per hour, fuel for the flight, fees for the instructor etc are all not known for being cheap.

It's not impossible. It's unfeasible.

Paying 3 hours of very expensive flight training to obtain 30min of actual flight instruction should be unfeasible at plain sight, but fair enough - the next level of detail is "makes it unaffordable, impractical, and is a strong deterrent for vast majority of interested parties".

>2. Lobby to get the flight training school to practice over unpopulated areas.

This is fairly typical — even in urban centers there's typically one or more "training areas" for students to practice maneuvers. e.g. in New York: https://i.imgur.com/Djum5pX.png

Try OpenADSB?

I think the issue is that military is permitted to fly without broadcasting anything, but the airspace is restricted to avoid civilian collisions. Or maybe de-facto clear by staying in high enough altitudes?

I have seen some military aircraft light up while practicing refueling over the pacific, but go dark when leaving or returning to base.

OpenADSB and ADSBExchange will definitely give you a better view of any military and private planes broadcasting ADSB.

The web map is entertaining to watch

https://tar1090.adsbexchange.com/

It's also good for making abstract art:

https://postimg.cc/vgG3PyW4

As a current student pilot, I have been doing a whole lot of circling. Hope no one thinks I'm the FBI in a ratty old C172. :)

When it comes to military aircraft, the situation there is kind of interesting. There's no general exception for the military, military aircraft are generally "required" to transmit ADS-B unless they have a specific reason not to (and I believe this requires authorization from somewhere up the chain of command). I put "required" in scare quotes though as many military aircraft are simply not equipped... the DoD has drug its feet on installing ADS-B out and the FAA has basically relented by setting very lax objectives. FAA requested DoD to have ADS-B installed on 21% of aircraft by the first of this year and I believe they met that goal... but it's still less than a quarter.

Over time more and more military aircraft should be appearing in ADS-B data, but I suspect it's going to be some years before it's almost all of them.

> Hope no one thinks I'm the FBI in a ratty old C172

C172 and C182 both make fine planes for running surveillance. They're inexpensive (to buy and operate), reliable, inconspicuous, and have enough space and useful load to tack on specialized equipment. I used to own a 182 that was originally owned by the Washington State Police. While in WSP service, it was modified to have an automotive-style muffler for "stealth" surveillance.

Yeah, I'm largely joking here, as I've seen a C172 in livery of the state police here before, and I don't think it was a new one either. The cops have payments to make too.

206s seems to be the most popular out there. Plenty of room in the back for the surveillance gear and there's a few companies that cater to fitting in all the gear in there (FLIR/TV tracking pod, additional radio gear etc.).

The step up are the B1900s that CBP has which have additional sensor capabilities.

B1900 is a few steps up. They have single engine turboprops (Pilatus PC-12 and Cessna Caravan) and the much more common ex-military King Air (the B1900's smaller ancestor.)

The California Highway Patrol mostly uses—or used, as of 10-ish years ago—206s. I know this because a member of my flying club was a patrolman who was trying to get enough hours in a C206 to switch to aerial patrols. We went on a couple of mountain flying trips to Colorado together.

According to him, the state much preferred to take cops and turn them into pilots, than to take pilots and turn them into cops. But anyone who wanted to go that route had to pay for their own flight time. (Commercial rating requires 250 hours, and I think they wanted at least a hundred hours "time in type." I don't think they required an ATP rating, but my recollection about that could be incorrect.)

Just FYI, they have almost fully upgraded their fleet to GippsAero GA8 Airvan's.

be careful flying around homesteads. My drone's been shot at before, and honestly given how the country's going, I dont blame them.

I believe the parent comment is referring to a Cessna trainer plane: https://en.wikipedia.org/wiki/Cessna_172

However, if you have a full-sized drone I would love to buy a kit from you.

> I expect this web site is similarly, deliberately, incomplete.

Perhaps less incomplete than you think (and certainly more complete than the standard tracking websites, which outside of hiding planes also must honor a 5-minute data delay requested by the FAA).

The advisory circular bots the author runs link to https://tar1090.adsbexchange.com/ , which is run from a home-grown network of SDRs. It makes a point of not hiding anything that reports its position with ADS-B -- which all aircraft (over a certain size) must report by law. I've even seen Air Force One and its escorts on this service, something that is always absent from other flight tracking services.

> 5-minute data delay requested by the FAA

Can you expand on this for the noobs in the subject?

so you cannot trivially go hit something with a ground-to-air missile.

why the downvotes? this was the actual stated reason when this was requested

Which is silly, because ground-to-air ordinance could just listen on ADS-B RF itself for the target (you too can listen in with a software defined radio if you're in the vicinity or have gear that can listen in the area). It's security theater, not an actual mitigation against a threat actor with access to an anti aircraft weapon.

For anything not broadcasting ADS-B, you can use multilateration (time difference of arrival) to determine positioning of dumb transponders. Flightaware does this [1].

[1] https://flightaware.com/adsb/mlat/

Umm, well, there is this issue that you can actually see the plane without a delay, so...

Requiring a line of site makes it much more difficult than giving real-time tracking data away

That's why The Rurists (Terrorists) try to hit a plane when it takes off or lands. Easier to hit. Even with a stinger. Just hang out by the airport with your favourite Stinger Launcher and you're good to go. No need to hit it at 30,000 feets. I'd hit it at landing takeoof the ground taxiing etc. Works for me.

No wonder that’s why 9/10 of the weekly terrorist takedowns of aircraft I read about are near airports.

Not sure why an answer to the question would be downvoted.

Anyway, it's possible that the reason was no so much ground-to-air missiles but rather ground-to-air weapons. In other words, idiots trying to shooting guns at airplanes or put up balloons in their path.

I suspect people downvoted it as a seemingly low effort post - ambiguous about whether it's a joke and no citation to indicate it isn't

I tried briefly googling, but while it's easy to find others talking about the delay [1], I didn't find a why confirmation

[1] https://aviation.stackexchange.com/questions/3052/is-there-a...

I had not heard of this rule before, but I'm guessing data sourced from the FAA is delayed by five minutes.

Most data on FlightAware, for instance, is from ADS-B feeders run by average folks. FlightAware takes this data and turns around to sell it for a boatload of money to people that manage fleets and want to know exactly where their plains are at. In order to ensure there isn't dropouts in coverage, FlightAware pays the FAA to feed them data that they can't get from ADS-B feeders, for example when a plane is not in range of any feeder. As a condition of the FAA giving them access to this data they must abide by the FAA's rules, one of which is filtering planes in which the owner has requested their tracking data not be made public.

Interesting fact, if you feed then you like contribute to FlightAware locating the position of an aircraft not emitting ADS-B, but with a Mode S (?) transponder. This is known as M-LAT, or multilateration. Because of FlightAware getting FAA data and being bound by FAA terms they won't return the position of the plane that you helped them locate, assuming the owner of that aircraft requested privacy. So essentially you help provid them the data that they can sell access to the owner of that aircraft, but you don't get to see that same data. Sites like ADSBExchange, which the OP app uses, do not source FAA data, and so are not bound by such crappy terms.

A lot of the commercial flight tracking services allow opt-outs. But some stay true to their mission.

FlightRadar24 certainly doesn't have a delay.

They also hide certain aircrafts.

In most cases I've personally witnessed (I have an RTL-SDR decoding ADS-B transmissions in the vicinity of my home) the interesting aircraft (e.g. fighters) are not operating an ADS-B transmitter at all, so there's nothing to hide. Some sites (adsbexchange.com comes to mind) do not filter anything.

About the only thing that's gone past me without any transponders are the civilian marked up Dauphin II used by the SAS...

ADSB Exchange does not. https://tar1090.adsbexchange.com/

As another commenter noted, not every aircraft advertises itself using ADS-B, but the majority do - even military. I’m no expert here, but I think the distinction is that military aircraft operating outside of civilian airspace don’t need to. But some do anyway - I’ve seen a U-2 flying at 62k feet over the Southwestern US show up on ADS-B exchange. There’s no need for it to do so, as no civilian aircraft flies at altitudes that high.

> must honor

Is this true? Seems like an unambiguous violation of the first amendment. Someone can't report on raw data that they can receive with an SDR? Has this been litigated?

> must honor a 5-minute data delay requested by the FAA

This only applies to FAA-provided data. And I'd not be surprised if it's simply enforced by the FAA only providing 5-minute delayed data.

Tracking sites that use ADS-B are definitely realtime. My kids and I sit outside on the patio sometimes and track the planes coming at our house (we're pretty close to one of the standard ingress routes to PDX).

There's a side-effect of having a big array of receivers; if you get the basic Mode S data that all aircraft (including military) transmit from their transponders, a little math lets you quickly plot their location using a technique called multilateration (MLAT) using time of flight data and a bit of trigonometry.

This uses ads b exchange so it shows a lot more than eg flightradar or radarbox.

Which app?

Are there several? If so what was the key features you were looking for?

>> The interesting and loud stuff that I see flying by out my window NEVER shows up on any app.

The slightly interesting stuff doesn't show up, the loud jets, but the really interesting stuff does. CIA rendition flights, police spying on protests, Air Force One, rich people flagrantly violating COVID rules ... they all squawk ADS-B.

I thought we/the usa stopped kidnapping people and torturing them with Bush2 leaving office. Is that not true? Any recent cases? I am aware we still keep people in Guantanamo and Obama and trump order the murder of people. But secret kidnapping was over I hoped. Maybe the next pres will stop extra-judicial killings?

Anybody halfway intelligent blocks the details that would otherwise be available with ADS-B, so the best you can do is see they exist, not identify the aircraft. This is often the case with corporate jets.

No, you can identify it on adsb-exchange. Sounds like you've been using flightaware/rb24/flightradar24 - they block aircrafts. https://tar1090.adsbexchange.com/

You can buy a Dotcom call sign subscription and fly your flights (including ADS-B ID) under a randomly assigned Dotcom callsign.

So, instead of being trackable N123AB, I could fly as DCM965. You could still potentially trace approximately where the aircraft flew (because there aren’t quite enough DCM flights for real anonymity), but it’s more work.

https://flttrack.fltplan.com/FltPlanInfo/DCMCallSigns.htm

The plane still transmits the hex address over ads-b.

https://www.planeandpilotmag.com/article/privacy-lost-in-the...

But in the case of the PIA program, the hex address that's broadcast in the ADS-B packet is unpublished, not associated with the tail number of the plane anywhere except in the FAA's internal database. It can be a very effective way of obscuring aircraft identity (though see the DEFCON youtube link I posted for potential vulnerabilities).

Yes, but the hex address transmitted is that of DCM965, not N123AB. On the next leg out, they could be assigned to fly as DCM398, etc.

I can enter a new aircraft ID into the box for each flight. That data is then transmitted in bits 9-32 of the ADS-B downlink message (where the N-number is typically transmitted for private aircraft).

Still wrong, here's a DCM flight live right now, it is transmitting its real hex which is tied to its registration. https://tar1090.adsbexchange.com/?icao=ad9e03

Yes, you can change the hex code your aircraft is broadcasting, but the FAA probably won't like that - they will want you to join the PIA program. https://www.faa.gov/nextgen/equipadsb/privacy/

All of which is clearly explained in under a page in Dotcom ID program I linked to. If you sign up for that program (which provides a third-party callsign assignment) and sign up for PIA and change the flight ID in your transponder, then you don't get tracking by N-number.

If you don't do all three of those things and keep transmitting your N-number via ADS-B, then you are trackable by N-number. That DCM2790 is using the same flight number for multiple legs and transmitting their N-number is evidence that they aren't maximizing privacy, not that privacy isn't possible.

There was an interesting talk at DEFCON this year about the FAA's Privacy ICAO Address (PIA) system, and potential attacks: https://www.youtube.com/watch?v=6-8z0z1swmE

Technical details are described here: https://gitlab.com/jjwiseman/advisory-circular/

Things flying near an airport are excluded ("The centroid of the last 3 minutes worth of positions must be more than 2.5 km away from all known airports."). I've never seen it tweet about planes doing obvious pattern practice.

It used to do a pretty good job of filter out pattern practice, but lately I feel like those false positives have actually become the #1 issue (maybe because my code was tuned for and worked fine around LA, but not other parts of the world). I'm working on some slightly fancier filtering to remove those.

If you're on iOS you want the "OpenADSB" app. I think I paid $10 for it but it's awesome. It doesn't filter out the military planes like FlightRadar24 does. But, sometimes FlightRadar24 has data that OpenADSB doesn't have, so both are still useful.

A few weeks ago I was watching an F-35 off the coast of Southern California... so cool to see that stuff. It seems to also pick up weather balloons (or some kind of balloons that are above 60,000ft). Anyway, it's fun to see what's out there.

I saw a U-2 spy plane a few weeks ago, flying over the SW US. I’ve seen a B-52 as well.

It used ADSBExchange as a data source.

Apps usually rely on ADS-B data, rather than IFF. US military planes to my knowledge don't use ADS-B.

They may not use it for anything, but I think they’re all able to broadcast it.

There was an initiative to have all of them able to by Jan 2020 but didn't address the security flaws of allowing anyone access to that information: https://www.c4isrnet.com/air/2018/01/25/gao-fix-security-fla... I know mode 5 is supposed to be a crypto version of ADS-B but not sure how many implement it https://en.m.wikipedia.org/wiki/Identification_friend_or_foe

It’s closer to 25% than 100% for ADS-B out equipage in the DoD fleet.

https://www.aviationtoday.com/2019/08/19/military-2936-aircr...

Have you tried https://tar1090.adsbexchange.com/ ?

Don't know if there is an "app", but regarding the interesting stuff, it's the most complete, IMO/E.

That's where the app sources it's data. If the military planes do not turn on their transponders then they can only be picked up on radar.

https://gitlab.com/jjwiseman/advisory-circular/

There’s a great app on iOS called OpenADSB. It’s not free, but worth the price. https://apps.apple.com/us/app/openadsb/id1178703539

I live in Baltimore. The GA aircraft you see circling over my town don't have students flying them.

Most of the helicopters belong to either TV stations or city/county/state police. There's also medevac, but they don't circle much.

Training circuits don't look like a circle at all.

This is what the standard training circuit looks like (it's basically a rectangular-ish shape)[1]

This is the type of orbit pattern that is used for search and rescue (SAR) or surveillance (a near-perfect circle, like the ones in the OP) [2]

[1] http://www.ppl-flight-training.com/circuits-briefing.html

[2] page 127 of this pdf ("Creating an Orbit Pattern") https://static.garmin.com/pumac/190-01007-03_r.pdf

Well, this is where we really get to the "low effort/high impact" philosophy: The bots don't look for circles. That's too hard/I'm too lazy. So they do something much easier, and generally better: They look for a net change in heading equal to 4*360 degrees.

  (defn curviness
    "Computes the total curvature of a sequence of headings."
    ^double [headings]
    (Math/abs
     ^double (reduce (fn [^double sum [^double a ^double b]]
                       (let [d (heading-diff a b)]
                         (if (spurious-heading-diff d)
                           sum
                           (+ sum d))))
                     0.0
                     (partition 2 1 headings))))

This is what allows the bots to find interesting activities I didn't think of ahead of time.

While the traffic pattern is indeed rectangular, the "flying in circles" may come off as almost a joke to people involved in flight training (at least it did to me as a student) because one of the maneuvers you are required to learn/be able to demonstrate is flying a perfect circle. So there are, almost comically literally, a lot of student pilots out there going around and around in circles. Also rectangles and S-curves and figure-eights, and I wonder if you could do a little filtering to pick up people practicing their stalls, but I'm not sure if the temporal resolution on ADS-B altitude is enough to get that.

Usually in urban areas there's a more or less formal designated practice area where people are doing these things, intentionally not near the airport, but you could filter out small aircraft in those areas if it was really an issue.

True, I didn't think of that but things like "hold a 30 degree turn for a certain amount of time" could indeed result in a circular flying path. You are right.

Reminds me of a program I read about a while ago in Iraq. Planes would circle cities with a camera and some huge hard drives installed. If an IED went off they would rewind the tapes, and watch every stop the people who planted it went through before and after planting the bomb. From that they could unwind very complex networks of insurgent activity. The equipment was mostly off the shelf, and relatively cheap.

"In Iraq" - they did it over US cities as well [0]. To be fair, I read that link a long time ago and don't remember the specifics of how long it ran and if it ran in more cities.

[0] - https://www.bloomberg.com/features/2016-baltimore-secret-sur...

Still going on... https://www.theguardian.com/us-news/2019/aug/02/pentagon-bal...

Yes, such drones have been flying over US cities with unrest this year as well[1]. It's likely surveillance in the form of ARGUS-IS[2], as it was reported to be on the platform used by the Gorgon Stare project[3].

[1] https://www.forbes.com/sites/krisholt/2020/05/29/cbp-predato...

[2] https://en.wikipedia.org/wiki/ARGUS-IS

[3] https://en.wikipedia.org/wiki/Gorgon_Stare

Can I just say that while the tech is no doubt a privacy concern, it was insanely incredible. They literally could track down where a person from any crime scene went to.

Use over US soil had been surprisingly limited, the only vendor really pushing for it is PSS and they proved to not be especially effective in selling the system after the Baltimore demonstration. It is possible that military equivalents (e.g. GORGON STARE) are being used over the US just recently but there's not a lot of evidence to that effect---but it's completely possible, the right kind of aircraft (MQ-9) has been used, it's just that the vast majority of MQ-9s are not so equipped so there's no smoking gun.

The TARS system is somewhat similar and has been used over the US but relies on a tethered balloon so it's not very mobile, I believe there are two of them, one in the DC area and one in southern NM. For a long time they were sort of infamously inoperational most of the time due to technical issues, and ten the DC one came loose and briefly terrorized Delaware, so I'm not sure how much of the time they're actually active right now. Every time I've gone by the southern NM TARS (not that often but probably several times a year) it's been down.

These overhead persistent surveillance systems are both technically interesting and extremely alarming from a privacy and civil liberties perspective, but it is surprising how little use they've seen in the US. Part of that owes to controversy over their use but honestly a larger part of it seems to just be ongoing technical difficulties in getting them to perform well. Also to be a little snarky I wonder if PSS's weirdly geocities-era website is a factor... when I was doing research papers on these a year or two ago I had a solid ten minutes of disbelief that that was really their actual website. It seems to actually be a very small company.

They used balloons: https://www.nytimes.com/2012/05/13/world/asia/in-afghanistan...

This is a good example of the "boomerang" effect[1] in which control techniques and developed for and used on imperial colonies, and are eventually brought back and used in the homeland.

[1] sometimes called the imperial boomerang, the colonial boomerang, or Foucault's boomerang

Here is one vendor who is trying to sell the technology to police forces in the US:

https://www.pss-1.com/

The most interesting reading is in the 'tracking police helicopters' slidedeck linked in the site: https://docs.google.com/presentation/d/1sowJrQQfgxnLCErb-CvU...

To those who notices planes flying in circles, it doesn't have to be anything sinister. Those might be planes calibrating avionics or ground/airport equipment or doing test flights after maintenance. I have agencies in the region doing both, so you can sometimes find planes doing strange patterns which are their clients.

Exactly. This doesn't mean that surveillance programs aren't taking place, but.... aspiring pilots gotta practice.

Pipeline and power line inspectors in helicopters also tend to have weird flight paths.

Commercial flights will also enter a circular holding pattern around airports if they're not allowed to land for some reason.

This video is a really cool example: https://www.youtube.com/watch?v=SdfVIdsufI8

Definitely agree! That's why the author has explicitly filtered out patternwork by excluding "circles" that are particularly close to an airport. It doesn't mean anything is sinister, but this project is definitely aware of and disinterested in just finding student pilots beating up the pattern.

When I was tracking flights some years ago (use case was determining whether speed monitoring aircraft were in the air, and a prediction model of their schedule) I learned that the ADS-B transmitters didn't need to broadcast GPS co-ordinates below a certain ceiling. You could get the signal that a given tail number was in the air, but if it stayed below a certain altitude, you couldn't always receive its location.

The FAA has guidelines on what kind of data you can receive: https://www.faa.gov/nextgen/equipadsb/research/airspace/

I lost interest in it because I just don't speed that much and I don't have a sport bike fast enough for it to matter, but useful to know that ADS-B doesn't cover all aircraft.

Oh that's interesting, I actually thought about that recently when I saw a "speed monitored by aircraft" sign on a highway. I wondered if an ADS-B receiver would pick it up. But... indeed, it's quite often that I see an aircraft and observe that it is not being picked up by my ADS-B receiver. Not sure whether due to low altitude , or that they are simply not transmitting..

> You could get the signal that a given tail number was in the air, but if it stayed below a certain altitude, you couldn't always receive its location.

I believe trackers (like ADS-B exchange) will estimate location using mutlilateration. IE: enough receivers with GPS-sync’d time and knowing where they are can estimate origin with the differences in receipt timing.

With good enough equipment, even one ground station might be able to tell a lot with Doppler shifts. Unsure if that’s don’t in practice though.

Looks like there’s much info here:

http://www.multilateration.com/downloads/MLAT-ADS-B-Referenc...

(Big PDF)

They use multilateration, but there's no GPS synced clocks needed. They use ADS-B messages with position as reference and uses the relative arrival times of those messages to model the clock characteristics of each receiver. That way all you need is an inexpensive receiver (like a RTL-SDR) and with enough receivers in an area you'll get pretty good position estimates of aircraft only transmitting Mode S messages.

This is the most popular mlat server software, used by ADS-B Exchange among others: https://github.com/adsbxchange/mlat-server

The regulations around ADS-B are pretty weird, basically because the FAA wants to require it of all aircraft but all the aircraft owners object because it's pretty expensive to install it. So the FAA has kind of been taking a "death by a thousand cuts" approach where they never quite "mandate" ADS-B but they require it in more and more situations...

So aircraft are perfectly allowed to not transmit ADS-B as long as they stay out of certain types of airspaces and outside of a certain distance of other types of airspaces and etc. So the effective result is pretty much that you need to have ADS-B if you ever want to land at a controlled airport but the details get a little weird.

These rules have also been changing reasonably quickly in federal terms. The current set of ADS-B requirements only took effect the first of this year. Among other things, these rules require that any aircraft equipped with ADS-B out have it turned on at all times... but that's only been the rule as of recently (not sure if this revision or the previous one), so not that long ago it was acceptable to turn it on and off if you were outside of areas where it was required.

Not all controlled airports, for example most class D airports are outside ADS-B required airspace. Basically, you need ADS-B in airspace where you already required a mode-C transponder previously.

Further nit: the rule went into effect on Jan 2 this year, because of the wording of the actual law. It seems likely that the intent was to be on the 1st, but that’s not what was written and enacted.

That's changed since 2020, you have to be far away from controlled airspace to just broadcast Mode-S anymore.

Not true. Most of the US is controlled airspace where you aren’t required to be ADS-B equipped. It’s a small minority of airspace under 10K MSL where it’s required (just class B veil and class C airspace and above class C rings). Most of class D and E airspace is not in the above category and therefore not ADS-B required while still being controlled airspace.

I ended up using some lockdown time to put together a Pi-based ADS-B receiver, as I live close to the main low-flying helicopter route through London. I've chosen to feed data to a mix of services, including ADSBexchange which powers those bots, so some of the data there comes from my receiver; which has a surprisingly long range with a decent antenna: I'm regularly tracking aircraft 190 or so miles away...

You can set up a system for under $120 with a good antenna and a 1090MHz-filtered software defined radio stick. I use the Piaware distribution, which sets up the basic software needed to feed data and to generate your own maps. An added bonus of being a feeder is that you can get free access to commercial ADS-B networks like Flightradar...

it seem cool but it bothers me that this is a link to a donation page and that its been obviously made to request money, rather than show the service provided

I find it oddly satisfying to be able to use an app on my phone to identify planes above me. Do it all the time. I live across the Puget Sound from Seattle and I occasionally end up spotting a Boeing plane clearly on a test flight based on the route it has flown (geometric shapes, circles, take-off and return same airport).

Also had an interesting occurrence when I awoke to the sound of a plane dive-bombing my house. We happened to be located in an area designated to be sprayed for some sort of moth. The plane was just about scraping the tops of trees. But I was able to track and see the pattern it flew to spray our area and other areas it had visited that morning.

I hope visitors are able to donate. Things have been tight this summer for a lot of people

TIL about iOS shortcuts. This shortcut is pretty cool. But the nearest airplane comes up as private and now I’m paranoid it is an FBI surveillance plane when it is probably just going to/from the local small field airport.

Why worry about the FBI if you're not in any of the categories where they have a reason to act? I doubt they care about your legal activities. They've probably got better things to do.

"Arguing that you don't care about the right to privacy because you have nothing to hide is no different than saying you don't care about free speech because you have nothing to say."

-- Edward Snowden

With regards to the FBI not caring about your legal activities, I recommend you look into the FBI blackmailing of Martin Luther King Jr. and COINTELPRO more generally. Their historic behavior doesn't exactly warrant trust.

Hiding something and expressing something are so nearly opposite that I don't see how Snowden's analogy holds

What he is doing is simply restating the "I have nothing to hide" argument in the context of a different right, in this case the right to free speech. He is doing so to illustrate that the argument is not presenting a justification for the systemic violation of a human right but instead relying on an unstated assertion that the a given persons disinterest in a specific legal protection is an adequate pretext for its removal.

That actually makes sense. Thank you for your reply.

My pleasure

By existing in a database, not only can your data and actions be taken out of context to make a damning case against you, you run the risk of being a false positive in an investigation[1].

In the case dragnet surveillance, you will constantly become a suspect in investigations based on where you were, what you look like, etc.

If your data doesn't exist in some database, at best you won't be caught up in a dragnet investigation. And at worst, your lack of data saves you from expensive court battles and imprisonment over something you didn't do.

[1] https://www.pbs.org/newshour/show/a-father-took-an-at-home-d...

Why do you assume my activities are legal?

Username checks out.

https://en.wikipedia.org/wiki/COINTELPRO

Recently we had a suspect run through the yard. It was terrifying and had I not been hanging out on the back room I would not have been able to lock the door before he got in. The initial tip off that something was off was the CHP plane flying in circles above.

Now when I hear the aircraft above us I instantly check its pattern and lock all the doors.

Oh jeez this is cool. The least we can do is get this guy a working Macbook Pro to continue his work. Donated!

I love what you're doing, but where's your website? You've got Twitter bots, but I'm not on Twitter, and a Siri integration but I don't own AAPL products. It makes me sad to see such useful data siloed in closed platforms.

I'm not happy about the dependence on twitter, either, but that's the platform that people are on, so that was my priority. Eventually I would like to run a Mastodon instance or other ActivityPub system.

But why no website?

I've also used Wolfram Alpha for similar information. https://www.wolframalpha.com/input/?i=what+planes+are+overhe...

How can this claim to be "all over the world" when your examples are "Los Angeles, Baltimore, Portland, Minneapolis, and London."

Last I counted, four of those five are in the same country. The world does not begin and end in America.

Oh my goodness, Mr. literal over here. There are currently 3 continents covered by Advisory Circular bots. There are actually more Australian cities than American cities covered.

You can see the complete list of bots here: https://twitter.com/i/lists/1263724487435890688/members

Maybe a link to the actual bots in the page rather than to a tweet with a twitter list that doesn’t seem to work would be helpful to, you know, actually see what’s going on?

This is the first I've heard that the twitter list doesn't work. What's the issue?

“Hey, Siri, what's overhead?”

Will probably see TACAMO relay aircraft with VLF trailing wire antennas.

hey, in the slide there was a part that says that surveillance planes typically flight in a couterclockwise circle. does anybody know why and can explain to me? thanks

Pilots are in the left seat, you get more visibility that way if you're "leaning" the plane to fly left circles.

ohh, thanks a lot

How would you feel when criminals use this?

Criminals can go to any of the commercial flight trackers and see most of this stuff, or to adsbexchange.com.

Someone needs to mention xkcd.com/1910/.

Nothing!

Cute, though I suspect the FBI have known the public knew about this, and alter their patterns for the most sensitive investigations. The real deal would be detecting when aircraft are in any cycle, regular or irregular, with similar visibility of a set of likely “targets”.

You might reach out to this author. Such a feature would be trivial to implement.

I might just do that; though you should see my list of side projects. There only so many hours in the day.

I believe this is the same project that surfaced a while back and the algorithm is remarkably effective for its simplicity, but I do agree that there are probably some others that would catch edge/sneaky cases.

The bigger issue are planes that are't showing up anywhere. I think it would be interesting to pair some audio and computer vision resources with existing ADSB network to train what planes sound like and possibly even which altitude/direction they are traveling based on sound energy alone.

Camera would be nice, also passive radar given that most of these ADSB tools are using existing software defined radios.

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