Here are the first few lines from a fllight log that I am following:
01:21PM 4214N/8321W 148 1700
01:22PM 4214N/8321W 147 2100
01:22PM 4215N/8321W 167 34000
01:22PM 4217N/8320W 200 3700
01:23PM 4219N/8319W 242 4500
01:24PM 4222N/8323W 218 7800
In the space of two or three minutes it says the plane climbed from 1700 feet to 34000 feet, dropped to 3700 feet and then resumed a normal climb. That would have been fun it was real!
It’s a weird bug in the data we receive. We have a proposal internally that has been passed around for eliminating that problem as well as other glitches. Seems like the rest of the data in that position report (besides the altitude) is logical although it’s probably best to consider that whole line unreliable.
To expand on Daniel’s comment, when an aircraft is cleared/assigned to a higher altitude, we often get a position report (from a different radar facility than the one tracking the flight) claiming the aircraft this there. We’re working on using more intelligence in interpreting the feed we receive from the FAA.
I’ve noticed that is very common a few minutes after departure, so I would agree that it is probably a byproduct of being cleared to a higher altitude.
Boy, that will be a challenge! GIGO??? 