Hot answers tagged

64

Most commercial aircraft transmit their GPS-based position twice per second. This is part of their Automatic Dependent Surveillance – Broadcast (ADS–B) broadcasts. The problem with providing world-wide receiver coverage for this system is that the frequency it uses only travels line via line of sight, so it won't travel past the horizon. Providing coverage ...


33

They have Mode-S transponders / ADS-B transmitters specifically for vehicles such a the ERA SQUID, Thales MOSQUITO or Saab Sensis VeeLoPDF. Typically vehicles that operate on taxiways and runways are equipped with such transponders, which ensures the vehicles can be tracked by the Advanced Surface Movement Guidance and Control System (A-SMGCS). Vehicles ...


30

FR24 relies for most of the tracks on ADS-B data. Part of the ADS-B transmissions is the position. There are three causes of the behaviour that you observe: 1). Aircraft landing next to the runway The position source onboard the aircraft is not always GPS. Mainly older aircraft (e.g. Fokker 100) have their Inertial Navigation System (INS) coupled to the ...


28

To answer your first question, ADS-B stands for Automatic Dependent Surveillance - Broadcast. Automatic in the sense that it operates without external stimulus (unlike radar) Dependent in the sense that the surveillance information is derived from on board systems Surveillance in the sense that it's primary intended to provide surveillance information to ...


26

Typically pilots do not know the 24-bit aircraft address of their aircraft. The 24 bit address is intended for data protocol level of communications and is not used in voice communication. Therefor there is no need for pilots to be aware of their ICAO 24-bit aircraft address. They use the aircraft's registration if they need to identify the aircraft they ...


20

The class of ATC radars that you are talking about is secondary radar. Secondary radar works by transmitting an interrogation signal on 1030 MHz to which the transponder replies on 1090MHz. There are several modes of interrogation. For civil ATC, modes A,C and S are important. The uplink signal (interrogation) is a simple pulse encoding (Mode A/C) or a ...


20

TLDR How will ADS-B actually reliably replace primary radar? It will not. Will GPS have become mandatory by 2020? Strictly speaking no, effectively yes. There are so many problems with that quote from FR24 that I don't know where to start. Let's take it apart and analyse it sentence by sentence. The percentage of aircraft equipped with ADS-B ...


18

The following is, in respect of aircraft, speculation. However, I did spend a decade working on the GPS based tracking systems mentioned in the question, with particular emphasis on remote operations in rural Australia. We did trial the use of Iridium, so I will comment on that too. Firstly such systems do not report in real time, that is baloney put out by ...


17

As GdD commented, the cluster you noticed is not near Denver, but Montrose, CO. The reason for this cluster is Wide Area Multilateration (WAM) with ADS-B. This technique uses many sensors distributed around an area to provide better coverage in areas with mountainous terrain that blocks a single radar or ADS-B station. Western Colorado is one such area that ...


14

The ADS-B signal used by FR24 is transmitted on 1090 MHz. Signals at that frequency do not follow the curvature of the earth very well. They work best in line of sight. Aircraft far away from the receiver must be at high altitude to be above the horizon. At 1000ft, the horizon is about 33 nautical mile away. Aircraft further away will be shielded below the ...


14

Not to take away from already great answer provided. In my experience the jumping behavior you are describing in Flightradar24 is due to MLAT triangulation that is used to establish approximate location rather than absolute (using GPS). Older planes transmit a SUBSET of ads-b data, which does not include aircraft location. So FR24 knows that there is an ...


14

Its hard to tell from the picture, but assuming you are talking about the yellow airplane and the "wiggle" in the course, that was probably just an S-turn for spacing. Sometimes the controllers don't get the spacing exactly right, or one airplane slows down early and messes things up. In those cases, in visual conditions, the controller can ask the ...


14

Yes, one can send deliberately wrong position reports. But why would anyone want to do that? We're assuming malicious intent, of course -- but even so? Could an attacker cause a collision using fake position broadcasts? It is hard to see how. The core meaning of an ADS-B broadcast is basically, "Dear ATC, please don't clear anyone to fly too near such-and-...


13

The short version is no the Stratus will not meet the requirements, and for several reasons. The final rule requires ADS-B OUT (and the Stratus is only ADS-B IN) that meets particular TSO requirements (see below), and portable units will not. The FAA has an ADS-B FAQ on their website which has a lot of great ADS-B information. The minimum equipment ...


13

For a short introduction on what ADS-B is and why it is called dependent see this answer. ADS-B is a surveillance technology whereby the aircraft broadcasts information about its identity, position, altitude and velocity of the aircraft to any interesting party. The position and velocity information is derived from GNSS (GPS). TCAS ADS-B is not intended ...


13

It depends on the type of ADS-B feed you have. On the lowest level, the messages transmitted from the aircraft, usually contain information about the air/ground status of the aircraft1. When the aircraft is airborne, Airborne Position Message are transmitted (types 9 - 18 or 20 - 22) for position and altitude. Airborne velocity is in message type 19. On ...


13

ADS-B is part of a system that compromises a number of different things. ADS-B (In) means that your aircraft is capable of receiving the ADS-B data, FIS-B and TIS-B as well. FIS-B broadcasts information such as weather. TIS-B is a traffic broadcast system. ADS-B includes a number of messages (about 27 different messages), including: Aircraft Identification ...


12

In the USA, ADS-B requires a WAAS position source. A Garmin 530W can be used, but not a 530. Here's a full list of FAA certified equipment needed for ADS-B. I hope that helps.


11

Compact Position Reporting (CPR) is a way of reducing the number of bits needed to transmit position whilst maintaining high position resolution (~5.1 meters for airborne encoding). Ordinary encoding would require 45 bits, but CPR uses 35 bits thus saving 10 bits. To do so, the world is divided up into a number of zones, both for latitude and for longitude ...


10

You aren't missing anything obvious, ADS-B spoofing (the sending of faked messages) and tampering (putting incorrect information into a message) is possible as there is no message authentication built into the protocol. The receiving station has no way to check whether messages are fakes. There are some proposed solutions here and here, to my knowledge there ...


9

I am going to assume you use Flightaware's variety of dump1090 as a decoder. When that receives a Mode A code, it publishes it as if it were a 24 bit address. The first two hexadecimal digits are filled with 'FF'. I have no idea why this may be a good plan. In mode_ac.c, lines 368-370: // Fudge an ICAO address based on Mode A (remove the Ident bit) // Use ...


8

ADS-C is used in oceanic environments, for example over the Atlantic and the Pacific. FL350 to FL390 on the North Atlantic Track System is restricted to ADS-C equipped aircraft. Non ADS-C aircraft have to fly either below or above those levels (crossing through those levels is permitted) The text below is a part of today's Norht Atantic Track message ...


8

In this answer I'll assume you are analysing ADS-B data on 1090 MHz, which is the defacto global standard. I am less familiar with the ADS-B on UAT (987 MHz) which is used in addition to 1090MHz in the USA, but I assume the same logic applies. There are no ICAO addresses assigned to TIS-B targets. If an aircraft has an ICAO-address which is detected by ...


8

The majority of commercial airliners are currently equipped. I don't have the latest statistics, but for Europe over 80% of the airliners were equipped with 1090 Extended Squitter ADS-B two years ago. The percentage in the USA was similar but a bit lower. That doesn't mean that all those aircraft are compliant with the European rules that mandate ADS-B for ...


8

On this question it is mentioned that ground support vehicles are equipped with ground transponders that work with the airport ground radar. I doubt they have ADS-B. They are most likely getting a feed from the ground radar system. In this thread on the Flightradar24 forum they discuss what types of ground systems are compatible with the FR24 recievers. One ...


8

It depends on what kind of Citation you are talking about. I found a presentation by Textron(ppt) that discusses ADS-B installation for various models. Textron is focussing on creating Service Bulletins (SB) for installation of ADS-B on recent models (up to 15-20 years old). For the Cessna Citation a SB is available for the following models: Pro Line 21 ...


8

Sorry, but windmills approach certified GPS systems do not work that way: A GPS approved for IFR navigation and approaches, like a Garmin 430W or GTN650 or an Avidyne IFD440, are more than just an approved position source such as what's included in the NGT-9000 transponder. They have an approved navigation database and interface with (or provide the ...


7

ADS-B, and the older Transponder Mode C, report pressure altitude. That is static pressure where the plane is expressed as altitude at which that pressure occurs in international standard atmosphere. In low pressure area, the same pressure density corresponds occurs at lower geometric altitude with similar difference at all altitudes. In higher temperature, ...


7

No, this is not being planned as a future update. The current ADS-B mandates of USA and Europe foresee ADS-B version 2 (EUROCAE ED-102A / RTCA DO-260B for 1090ES) to be implemented in 2020. Work on the development of version 3 of the standard has started but the retransmission of received data is not foreseen currently. Because of 1090 MHz spectrum overload, ...


7

ADS-B UAT operates on 978 MHz and are available for aircraft that operate below 18,000 FT MSL. UAT transceivers can display aviation weather products (FIS-B) as well as traffic from ground radio stations (TIS-B). The airplane must be in a coverage area for TIS-B services. TIS-B is intended to provide ADS-B equipped aircraft with a more complete traffic ...


Only top voted, non community-wiki answers of a minimum length are eligible