Many if not most posters here don’t understand what ADS-B is, and how public sites such as ADSBExchange/Flightaware/Flightradar/Radarbox/RealTraffic alter that data (or not). This results in two extremely annoying camps forming: Camp A who take ADS-B data for gospel, and camp B who decry any publicly sourced ADS-B data as made up and false.
Both are dead wrong.
The very short explanation is this: ADS-B messages are a digitally encoded data packets, transmitted at 1090 MHz, containing information about the state vectors of the transmitting aircraft. If a receiver was able to decode the message and the checksum was correct, the data is real as measured and broadcast by the aircraft. There is no guesswork involved in this - it’s true information.
But: Not all state vector data is sent in each message. Vertical speed and altitude are broadcast up to 10 times per second. Position and GPS derived speed up to 4 times per second. Other parameters less frequently. The Callsign for instance may only be transmitted once every 2 seconds.
So it is up to the ADS-B data aggregators (i.e. FR24, ADSBExchange, …) to FILL IN and SUBSTITUTE data that is not present in messages with data from previous messages. What’s more, a position update rate of several times a second is not feasible to use on a tracking website. So all tracking websites aggregate the data, and each web browser connected retrieves the information once every 10 seconds or so.
That is why some websites such as FR24 use extrapolation when displaying aircraft on their websites, so the update on the display is quicker than the actual data rate. The data itself with MOST tracking websites updates in 10 second intervals. Any position updates you see inbetween are generally extrapolated positions based on the previous track and speed. Those extrapolated positions can’t be trusted of course, as they are the guesswork of software.
To avoid using guesswork when analysing an accident, you therefore can’t use the web displays, but you have to download a CSV file from FR24 or Flightaware or ADSBExchange and only use the data points presented there. These points have a very high degree of reliability - but you must be aware of the system’s limitations. You may for instance see position updates but the altitude or vertical speed remains the same. That doesn’t mean the altitude or vertical speed hasn’t changed, it’s possible no altitude message has been successfully decoded and passed on. The data aggregators then may cross fill altitude from previous data points. If you don’t see the altitude change, it may or may not be the same. But if the altitude field has changed, then a new altitude has been received. It’s simple, really.
So by all means, use the publicly available data and try and interpret as much from it as you can. But be aware of its limitations and make adequate use of the space between your ears!