Bjorn’s Corner: Largest navigation change since radar

Bjorn Fehrm

June 15, 2018, ©. Leeham News: The worldwide aviation is heading for its largest navigation change since VOR and Radar was introduced after the Second World War.

When scheduled airline traffic started in the late 1920s, navigation was with maps and when the weather was bad, through Low-Frequency Radio beacons. Then the VOR and Radar were introduced. Now we will replace these as well.

A new navigation and separation system

We have navigated civil air traffic with a combination of VOR, Radar and gradually GPS over the last decades. GPS will be with us going forward, as the way to know where we are and where we shall be going. But it doesn’t keep us from running into one another.

We have been using Radar for this and where it has no coverage we rely on time separation of aircraft flying after one another in corridors (over the Atlantic and Oceans). Lately, collision warning systems have warned for aircraft nearby your own aircraft.

At first, the surveillance with ground-based radars relied on its own signals, needing no cooperation from the aircraft. But a radar return on a display doesn’t say who is up there. For military purposes the radar was complemented with an IFF (Identification Friend or Foe) interrogator, triggering the aircraft to send a response if it was friendly.

Soon the civil radars were equipped with a civil version of the IFF, triggering a response from the aircraft’s civil IFF, the Transponder.

We now had radar traces and a coded signal from the poked Transponder who said whom it was (Mode A Transponder). Soon the Mode C Transponder was added which could return the altitude of the aircraft to the radar operator as well.

Gradually several radars could paint an aircraft at the same time, triggering several Transponder responses, thus saturating the system. The Selective Transponder S was introduced, which only triggered a response to the radar addressing it directly (with a code, getting it a coded response).

Combined with VOR or GPS, who helped with the navigation, this is how we have navigated and informed the Air Traffic Control (ATC) where and who we are.

A total change

Today’s system relies on the aircraft being asked to respond with its code and information (altitude for mode C Transponders, Heading, Speed, Vertical speed … for Mode S Transponders).

A new system will be mandatory on the aircraft side from 1 January 2020 in the US and it is gradually introduced for the rest of the world.

The fundamental change for the new system is; it requires no interrogation (poking) of the aircraft. Instead, the aircraft sends a complete information package every second of whom it is, what it’s doing and what its intentions are to anyone who cares to listen.

This means everyone who has a receiver for these signals; other aircraft, ATC, Flightradar 24 enthusiasts,… have full knowledge of:

  • Whom the aircraft is
  • Where the aircraft is
  • Where it’s heading, at what altitude and at what speed
  • If it’s climbing or descending
  • If it’s in distress

The function in the aircraft sending these pieces of information is called ADS-B (Automatic Dependent Surveillance-Broadcast).

How the aircraft sends own ADS-B signals and receive others and what all the players do with these signals we will cover in the next Corners.

17 Comments on “Bjorn’s Corner: Largest navigation change since radar

  1. O, you won’t believe what they’re doing now. Let’s go home to Dayton. W

  2. It might be a problem as the info sent out with ADS-B would make missile shots that much easier as the missile reads the information sent out. Maybe coding the signal and some frequency hopping can make it buyond “normal rouge state” capabilities.

    • If anything I’d like to see the data transmitted loud, wide, and in the clear. Of the 20 or so shoot-downs since the ’70, most were due to misidentification. Incidents like KAL 007, Iran Air 655, and Malaysia Flight 17 are the real danger.

      A lot of easier ways to shoot down aircraft than inventing, engineering, and building a missile with a whole new guidance methodology. A DHL 737 was hit over Bagdad in 2003 with an old Soviet SA-14.

      • Yea, its not like a commercial airliner with no defensive measures is nothign more than a bit fat target to even the WorldCat radar (at missile range)

  3. A seeker as the one in the earlies Sidewinder rocket (and the rocket in it’s entirety) is so simple that you wouldn’t go the GPS road even with unencrypted GPS feed … and one should keep in mind that there are a lot MANPADs out there. One tapping into the GPS coordinates send out by the aircraft sounds like a movie plot threat. BTW: Foiling this would be easy to. A sidewinder has an effective kill ratio of 10 meters. let’s say to be sure, you have to keep the rocket 100 meters away. With current horizontal separation minima you could send an aircraft poistion that is at any angle to the aircraft at least 100m away from the aircraft in a random angle to the aircraft.

    • Surely at a range of 100 metres the IR seeker would easily do the rest?
      It might make it easier for idiots like the 53rd regiment Kursk to avoid acquiring innocent airliners.

      • I assume a half way decent IR seeker … (even if you just rebuild the seeker of the 50ies Sidewinder ) doesn’t need help when fired at an commercial airliner.

  4. Well things are not exactly as a series of technologies piling up on each other, the last one potentially replacing all the others.

    A primary purpose of ADS-B is to enable a surveillance service in areas where radar coverage is insufficient (e.g. due to relief) or non-existing.

    As already experienced by Australia for several years , with a proper equipage mandate, ADS-B can serve as sole cooperative surveillance means (taking over SSR radar for not-so-dense traffic areas) while non-cooperative surveillance remains achieved by primary radars.

    As long as not everyone is equipped (here costs for retrofitting old aircraft maybe prohibitive), the targeted benefits of having a ‘traffic picture’ for everyone do not materialise.
    Having ADS-B ground stations inter-connected here allows to determine the position of non-ADS-B aircraft, using Mode-S transponder signal (broadcast with no interrogation required as well). This is called Multi-Lateration (MLAT) and this technique is already in use at large airports for several years.

    Facing FAA 2020 mandate for transport aircraft equipage, US DOD has recently required to assess the related security issues.
    So the storyline may get different after all.

    • Aye, there’s the rub: “As long as not everyone is equipped … targeted benefits … do not materialise.” Quite.
      I’m not sure if it still holds true, but a rule of thumb used to be that there were about 300,000 civil aircraft, of which two thirds were in North America, and that about 10 percent of all civil aircraft were in public-transport operation. Of course, very many in the general-aviation community (but usually not those in business/corporate/executive operations) will have reasons why they should be exempt — although that argument might already have taken place?
      Ironically, it was very often those wanting to be independent who were the first to use GPS for navigation — well before it was judged to be sufficiently accurate and when local differential correction was needed. As I remember someone pointing out 40-50 years ago, for inertial navigation to be accurate to, say, half a mile after a 3,000nm transatlantic flight was “pretty good, unless it’s the distance to baggage reclaim.” Nor pretty good if it’s the touchdown lateral deviation from the runway center line…

      • The ADs system (Called Capstone) was first trialed in Alaska build by local FAA in whats called the Western Region, worst weather in AK (other than Aleutian Islands ) 500+ miles North to South, 200 wide and lots of villages and some small towns, lot of air traffic with Single engine (206, 180, Caravan) – so there is small and reasonably priced equipment for small aircraft.

        AK Airlines got it added to South East AK as they have 4 very tough airfields down there that weather and terrain is a serious issue.

  5. ADS-B was invented at Lincoln Laboratories in Lexington, Massachusetts by Dr Paul Drouilhet. Sadly, my good friend Paul passed away earlier this year. Briliant mind. Extraordinary person.

  6. Well the things are not exactly like a series of technologies piling up or one replacing the others. Choice is driven by type of usage and performances.

    A primary purpose for ADS-B is to enable a surveillance service where radar coverage is partial (e.g. due to relief) or non-existent.

    For several years Australia has replaced cooperative surveillance with radars by ADS-B, having put a mandate for all transport aircraft. Non-cooperative surveillance remains with primary radars.

    Given the costs and delays involved for equipage (100 000+ aircraft to retrofit in US) and emerging security issues (raises by US DOD) having a ‘traffic picture’ for everyone for free from 2020 is not necessarily the only storyline.

  7. I’m thinking that, much as the FAA bureaucracy doesn’t want to budge, they’re going to have to move the 01/01/20 compliance date. I’ve seen estimates varying from 40,000 to 60,000 noncompliant aircraft at that date. Food for thought: A two year extension?

  8. Once the new system is in place (satellites and all), it probably is a better system on all levels – one would think…

  9. Do/would pilots have the option of shutting ADS-B off like they currently can with transponders?

    • Yep, happens all the time in Western AK, they don’t like some part of it (usually terrain avoidance) and of course they auger in.

      Different purpose than the link coms to track aircraft per MH370.

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