Air-Traffic Control Is in the Midst of a Major Change from Radar to GPS • Hacker News Board

Re: Air-Traffic Control Is in the Midst of a Major Change from Radar to GPS

#111

Post by zentiggr » Fri, Jan 24, 2020, 6:05 PM UTC

jaywalk wrote: post #77

onepremise wrote: post #44

I worked for a firm, which studied satellite navigation and implementation for air traffic control, guidance, safety, and ILS. I don't think that will ever happen. There are huge gaping issues with GPS, both WAAS and GBAS. It's very unreliable, especially in bad weather. The old-school RF tower and ILS, which used Carrier frequency pairings by the runway, are way more reliable and propagate bad weather while guiding…

> Even the GPS signal itself has latency and lag What do you mean by this? You sound pretty knowledgeable, so you must know that it's simply not possible for the GPS signal to have latency or lag.

It's actually impossible for GPS to show your current position.

The signals have to be received from each satellite, then processed to yield a position valid at the time of transmission.

Every GPS fix you get is delayed by AT LEAST that processing time. Any filtering adds more lag.

Most navigation systems look at the T(fix) -> T(now) difference and project your now position from the prior fixes. Especially if you're following driving directions as opposed to free movement, then programs like Maps etc project how much further you've moved on the route, not just along your velocity vector.

After a few seconds, though, that projection will stop moving, too, when the gap between last fix and now gets too large.

Re: Air-Traffic Control Is in the Midst of a Major Change from Radar to GPS

#112

Post by tdhoot » Fri, Jan 24, 2020, 6:11 PM UTC

Patrick_Devine wrote: post #109

FabHK wrote: post #76

Earlier quoted context omitted.

> buying an aviation radio off the shelf and just chatting on the frequency or issuing fake clearances if you want to be a mass murderer Incidentally, I am happily surprised that that never seems to happen. One could so easily create so much chaos at an airport... There is no authentication whatsoever.

The problem with _requiring_ authentication is that it can create a safety issue when communications break down. As a pilot it's not a bad idea to carry a spare handheld radio, or even use a cel phone, when you lose communications. I was flying once with a buddy of mine who was Pilot-In-Command and we lost (or thought we had lost) our radio on an IFR flight back into the Bay Area. What had happened was the Push-to-Ta…

Pilots do train for communication failures. ATC at most airports has a number you can call to be patched through if your radio stops working and I've heard multiple cases of people having to use it.

In the worst case, there are non-verbal methods of communication that pilots or ATC can employ (ATC can send light signals, pilots rock their wings to signal communication failures, etc.)

Re: Air-Traffic Control Is in the Midst of a Major Change from Radar to GPS

#113

Post by leetrout » Fri, Jan 24, 2020, 6:17 PM UTC

Patrick_Devine wrote: post #109

FabHK wrote: post #76

Earlier quoted context omitted.

> buying an aviation radio off the shelf and just chatting on the frequency or issuing fake clearances if you want to be a mass murderer Incidentally, I am happily surprised that that never seems to happen. One could so easily create so much chaos at an airport... There is no authentication whatsoever.

The problem with _requiring_ authentication is that it can create a safety issue when communications break down. As a pilot it's not a bad idea to carry a spare handheld radio, or even use a cel phone, when you lose communications. I was flying once with a buddy of mine who was Pilot-In-Command and we lost (or thought we had lost) our radio on an IFR flight back into the Bay Area. What had happened was the Push-to-Ta…

Now I'm trying to remember if the radios have TX lights that would help show that you are transmitting...

Re: Air-Traffic Control Is in the Midst of a Major Change from Radar to GPS

#114

Post by jcrawfordor » Fri, Jan 24, 2020, 6:19 PM UTC

ufmace wrote: post #104

jcrawfordor wrote: post #89

Earlier quoted context omitted.

In the US, ATC radar and military radar are one and the same - the FAA and the Air Force share the Joint Surveillance System (JSS). So, while the JSS has plenty of limitations (including plenty of areas with no coverage even in the mainland US), it's designed to meet the military objectives of being able to locate even non-cooperating aircraft. The JSS is a descendant of the SAGE system developed during the Cold War…

Well that's interesting. How does that tie in to the story's reported change though? I suppose ATCs might be willing to rely solely on aircraft-reported location and speed, but I kind of doubt the USAF would. If they share the same systems, I suppose no equipment would actually change or be decommissioned.

I think that the article's implication that radar is being 'replaced' refers only to the daily work of controllers, not to the technical system. Both the FAA and the Air Force have strong motives to keep the primary radar system, and it would take many years to decommission it even if they wanted to - but near-100% availability of ADS-B does mean that controllers will use it as their primary source of data, instead of relying on the radar returns which even in areas with good coverage can sometimes come in and out and generally be finnicky.

Consider that controllers currently rely primarily on secondary radar, which while more difficult to spoof than ADS-B is still quite subject to malicious manipulation. They are well aware that a primary radar return with no corresponding secondary radar information is something to sort out, and this won't change with a switch to ADS-B.

Re: Air-Traffic Control Is in the Midst of a Major Change from Radar to GPS

#115

Post by jcrawfordor » Fri, Jan 24, 2020, 6:23 PM UTC

ceejayoz wrote: post #60

mattlutze wrote: post #46

Earlier quoted context omitted.

Have you seen any official discussion of the data being made available? I feel like, for example, I'd be worried if fine-detail GPS data was being published live for example, or live enough to predict where the plane is "right" now...

It's been live for years. https://flightaware.com/live/ Any time my dad takes his personal plane up for an hour's flight, I get a text message and can watch his track (and altitude/speed) in real-time.

It's worth noting that this kind of data isn't published by the FAA - rather, ADS-B transponders openly transmit information and anyone who wants to is (at least technically) free to receive it. This includes commercial and hobbyist networks of receivers that report information to web services like this.

The FAA in the US does publish a 'privacy list' of aircraft whose owners have requested that they not be included in services like this, and most commercial providers comply with that list, but enforcement is sparse and several hobbyist projects (e.g. ADS-B Exchange) do not and even emphasize aircraft that have put in such a request, since the tend to be a bit more interesting. A bit of a Streisand effect.

The same situation exists with the similar AIS system used by ships at sea, and has produced concerns over malicious use, but there continue to be plenty of websites that will show you maps of ship locations picked up by their contributing AIS receivers.

Re: Air-Traffic Control Is in the Midst of a Major Change from Radar to GPS

#116

Post by jcrawfordor » Fri, Jan 24, 2020, 6:27 PM UTC

LargoLasskhyfv wrote: post #98

korethr wrote: post #94

Earlier quoted context omitted.

I'm kind of wondering if there even needs to be. If you keyed up on frequency near a major airport as described in the GP, I'm pretty sure the FAA and FCC would be working together to track you down in short order. I could see the argument that it would be good to add authentication to the radios to complement the strict enforcement for a sort of belt-and-suspenders approach. However, I think a more pressing concern…

Could they? A moving target? Say the soundproofed back of some van.

VHF radios are relatively easy to locate by direction finding techniques, using for example a doppler direction finding array. The FCC's enforcement division is well-known to possess SUVs with this kind of equipment discreetly installed, although due to their famously limited budget you aren't too likely to see one in the wild. On the other hand, though, many large airports have such equipment permanently installed (e.g. RFEye).

Re: Air-Traffic Control Is in the Midst of a Major Change from Radar to GPS

#117

Post by xxpor » Fri, Jan 24, 2020, 6:29 PM UTC

Patrick_Devine wrote: post #109

FabHK wrote: post #76

Earlier quoted context omitted.

> buying an aviation radio off the shelf and just chatting on the frequency or issuing fake clearances if you want to be a mass murderer Incidentally, I am happily surprised that that never seems to happen. One could so easily create so much chaos at an airport... There is no authentication whatsoever.

The problem with _requiring_ authentication is that it can create a safety issue when communications break down. As a pilot it's not a bad idea to carry a spare handheld radio, or even use a cel phone, when you lose communications. I was flying once with a buddy of mine who was Pilot-In-Command and we lost (or thought we had lost) our radio on an IFR flight back into the Bay Area. What had happened was the Push-to-Ta…

Here's an example of a AA B757 in essentially that exact situation after taking off at JFK: https://www.youtube.com/watch?v=Wcq6KipBOro

Re: Air-Traffic Control Is in the Midst of a Major Change from Radar to GPS

#118

Post by jiveturkey » Fri, Jan 24, 2020, 6:34 PM UTC

jrockway wrote: post #67

A lot of comments seem to be about spoofing. Remember that there are multiple humans in the loop -- experienced pilots and experienced air traffic controllers -- and multiple levels of redundancy. Pilots have access to barometric altitude, radar altitude, traditional VHF navaids, TCAS-issued resolution advisories (based on directional antennas, not GPS)... in addition to GPS. Air traffic controllers have primary rada…

> Air traffic controllers have primary radar and secondary radar in addition to ADS-B information.

Article is pay-walled so I didn't read, but the title explicitly says 'from Radar to GPS', ie away from Radar altogether. It doesn't say, GPS to supplement radar.

Re: Air-Traffic Control Is in the Midst of a Major Change from Radar to GPS

#119

Post by AWildC182 » Fri, Jan 24, 2020, 6:35 PM UTC

TkTech wrote: post #88

qrbLPHiKpiux wrote: post #79

Earlier quoted context omitted.

But the risks and consequences are catastrophic. The Feds will put you away forever for even attempting it.

And most major airports have systems like RFEye or AIRPORT-SHIELD. You would be _immediately_ pinpointed with a remarkable level of accuracy from 3-6 sensors. Especially near major metro areas, unintentional interference is a daily issue. These systems immediately triangulate sources of interference in a wide band. Or you have simpler systems like UMS100 that just do alerting and you send out an engineer with a wand…

These could be pretty easily defeated through a multitude of tactics. They're just being pitched as a stop gap solution against the low hanging fruit like morons with drones or a drunk person with an airband handheld.

Re: Air-Traffic Control Is in the Midst of a Major Change from Radar to GPS

#120

Post by jaywalk » Fri, Jan 24, 2020, 6:35 PM UTC

zentiggr wrote: post #111

jaywalk wrote: post #77

Earlier quoted context omitted.

> Even the GPS signal itself has latency and lag What do you mean by this? You sound pretty knowledgeable, so you must know that it's simply not possible for the GPS signal to have latency or lag.

It's actually impossible for GPS to show your current position. The signals have to be received from each satellite, then processed to yield a position valid at the time of transmission. Every GPS fix you get is delayed by AT LEAST that processing time. Any filtering adds more lag. Most navigation systems look at the T(fix) -> T(now) difference and project your now position from the prior fixes. Especially if you're…

The position output by a GPS receiver certainly can (will) have lag. That's probably what the poster I replied to was referring to, and I hadn't thought about it.