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I want to understand what is the purpose of doing localization while an aircraft is flying? What sensors are used by the instruments that do this localization of an aircraft? Is there more than one way to do the localization? Can we do localization without using a GPS? How is magnetic heading used to do localization?

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    $\begingroup$ Can you clarify what you mean by "localization" - I understood it as "what is the purpose of knowing where you are?" - which seems kinda obvious. $\endgroup$ – Jamiec Nov 13 '20 at 8:07
  • $\begingroup$ I think it's meaning is related to navigation and current location of an aircraft in air. $\endgroup$ – scico111 Nov 13 '20 at 9:34
  • $\begingroup$ When my father flies his Piper Cub, without any electronics at all, including no radio, his localization is usually "looks out the window" :) $\endgroup$ – CGCampbell Nov 13 '20 at 16:23
  • $\begingroup$ Are you asking about the localizer portion of an ILS approach? I am guessing that you heard this term and are using it in your question, but not in the correct context. If you just want to know what a localizer is there is plenty of information out there. Or you could just ask that. As is, the question needs clarification and I am voting to close. $\endgroup$ – Michael Hall Nov 13 '20 at 18:30
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I want to understand what is the purpose of doing localization while an aircraft is flying?

Well, in general it would be nice to know where you currently are, wouldn't you agree? Even aircraft flying under VFR (Visual Flight Rules) should be able to determine their location, either by looking out of the window and identifying landmarks they know or by tuning in VORs. Knowing where you are is obviously important for finding your way to your destination airport, but it also helps to find a suitable diversion airport in case of an emergency.

Most IFR (Instrument Flight Rules) flights today are capable of RNAV (Area Navigation), which means they navigate based on knowing their own position rather than following ground based radio signals (like VORs or NDBs). This obviously implies that they need to have accurate localization.

What sensors are used by the instruments that do this localization of an aircraft? Is there more than one way to do the localization? Can we do localization without using a GPS?

There are multiple ways to determine the aircraft's position. The oldest standalone system is an INS (Inertial Navigation System). This system is aligned on the ground and you need to enter the current position. It will then keep track of the aircraft position by integrating all rotations and accelerations by measuring them with gyroscopes and accelerometers.

Such INSs are part of a modern airliner's ADIRU (Air Data Inertial Reference Unit) today. Because of inaccuracies in the measurements, the inertial position will start to deviate from the true location of the aircraft over time, which is called drift. This drift can be corrected by a radio based update (e.g. DME/DME), where the location is determined with radio based signals. Today, it is more common to use a GNSS (like e.g. GPS) to do these drift corrections. GPS is however not required for the ADIRU to work.

Smaller aircraft typically do not have an INS. Many modern GA aircraft have a GPS unit installed, which will provide location. For these units, GPS is required, and if it should fail, the location would be lost. The pilot can then still use conventional navigation (e.g. VOR to VOR) to navigate.

How is magnetic heading used to do localization?

The magnetic heading is just the direction in which the aircraft is pointing (using magnetic rather than true North). This alone will not give you any localization.

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I want to understand what is the purpose of doing localization while an aircraft is flying?

Knowing where you are means you won't get lost and arrive at your destination instead of literally anywhere else.

What sensors are used by the instrument that does this localization of an aircraft? Are there more than one ways to do the localization? Can we do localization without using a GPS? How does magnetic heading is used to do localization?

These are all highly related questions. Yes, there's more than one way to do it and most ways don't involve GPS. The "instrument" is usually a pilot combining the different sensors, or a flight computer in more advanced airplanes.

  1. Looking out the window and checking with a map. Suffices for most VFR flying. A compass can help with orientation.
  2. GPS. Quick and easy, but requires pretty expensive instrumentation. A much cheaper handheld tablet may be used to help with VFR navigation.
  3. Radio guides. VOR and NDB can be used to see what bearing you are relative to beacons on the map. Using more than one, you can triangulate where you are. VOR/DME can be used to get your position with just one beacon. Requires a map with known beacons. ILS can help you get to the runway.
  4. Inertial navigation system (INS). Extremely sensitive equipment register all accelerations, and by integrating twice determine position. Errors add up over time, so other sources can be used to periodically correct for this.
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