This is an ongoing flight details of my in-laws travelling from Frankfurt to India. I observe the speed of the craft is drastically reduced to 100mph and then picked up normal. Could someone please explain this?

enter image description here Thanks, Raj

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    $\begingroup$ The process that FlightAware and similar sites use for data collection is not perfect. Sometimes incorrect data is added to their databases that shows up as odd changes in speed, altitude or position. Nothing happened to the aircraft - it's just a faulty database entry. $\endgroup$
    – user27769
    Jan 4 '18 at 18:12
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    $\begingroup$ 100%, this is a glitch in the data. Very common, I've had to deal with this before. $\endgroup$
    – Johns-305
    Jan 4 '18 at 18:14
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    $\begingroup$ See also this question and answer for a similar issue with explanation - travel.stackexchange.com/questions/84462/… $\endgroup$
    – Moo
    Jan 4 '18 at 18:48

What you are seeing is merely a glitch in the publicly available telemetry sites like FlightAware use.

They aggregate flight data from the FAA (ASDI), EUROCONTROL and others to feed their sites, but this data is not always accurate, and doesn't need to be.

For that interval, the speed was either malformed or reported as 0/unavailable (don't remember exactly) due to bad data.

The aircraft did not slow to 100mph or lower unless it landed :)