Originally Posted by
TwoHeadedTroll
Running the numbers: The vertical speed three times touched 30,976 feet per minute, which is exactly 600km per hour.[...]It is suspicious that the vertical speed peaked three times at exactly 600kmh (I am suspicious of round numbers).
Actually 30,976 feet per minute is about 566 km/h, not 600 km/h. But you are right to be suspicious about that number, because it's quite close to the maximum vertical speed that can be encoded by ADS-B: 32,640 feet per minute (597 km/hour). So it wouldn't surprise me if that
30,976 fpm value is the maximum that can be reported by this particular type of aircraft due to some additional limitation, and the actual vertical speed probably reached even higher values.
ADS-B encodes vertical speed as a 9 bit integer (there are also two additional bits for direction - up/down - and source - GNSS or barometric), and each increment of that integer represents 64 feet/minute. So there are only 512 possible values for vertical speed, between 0 and 511. And because 0 is regarded as "no data", you have to substract one from that encoded value before multiplying by 64. That gives a maximum of 510 x 64 = 32,640 feet / minute. You can't get more than that encoded in an ADS-B data packet.