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I am working with a big ADS-B traffic sample of one day Europe, and identified repeated call signs. Examples include:

  • Flight that ends in an airport and repeated call sign starts from there.

  • Two flights with the same call sign, ADEP and ADES.

  • Four Different ADEP and ADES.

I thought in one day it was not possible to have repeated call signs. Is this possible? Is my data wrong?

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It is no problem to have the same call sign on the same day. As long as the same call sign is not uses at the same time there is no problem.

For VFR flights, the same call sign can even be used at the same time as long as it is not in the same airspace.

Many of the ADS-B duplicated call signs on a single are aircraft registrations coded in the transponder's aircraft ID field, typically from General Aviation flights

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  • $\begingroup$ Thank you for your response. A related question: Should call signs be ICAO codes? I detected plane models that appear as call sign: CL60, CL30, B737, B738... and some strange call signs like 1234ABCD. $\endgroup$ – Daniel Viaño May 31 '17 at 9:53
  • $\begingroup$ I have rarely seen such aircraft ID's being transmitted. What is the source of your data? Is it from FR24 or similar? $\endgroup$ – DeltaLima May 31 '17 at 9:59
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    $\begingroup$ They modify the call signs based on other information they have; what you see in not what was transmitted. For many aircraft they will withhold the identity of the aircraft and replace the call sign by a generic type identification. $\endgroup$ – DeltaLima May 31 '17 at 10:04
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    $\begingroup$ @DanielViaño Those 8-digit codes are internal FR24 identifiers. Read this answer about those $\endgroup$ – TomMcW May 31 '17 at 17:15
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    $\begingroup$ @DanielViaño Also, I've found FR24's system to be really glitchy. One aircraft turns into two quite often. I'm not sure why but I suspect it's due to their system anticipating the path in between ads-b updates. I think it must confuse the system sometimes when an aircraft is in a different position than the computer expects it to be, so it ends up creating a duplicate "ghost" aircraft with the same call sign $\endgroup$ – TomMcW May 31 '17 at 17:23

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