loss of altitude


Can someone help? I have been tracking QANTAS flight 108 over a number of days and when I click on the “track log” which shows a minute by minute progress re speed and altitude, I have noticed that in some cases there is a massive loss of altitude in the space of a minute. Here is an example:
08:13PM 40.35 -74.15 339 12400
08:14PM 40.30 -74.27 352 15600
08:15PM 40.25 -74.38 363 36000
08:16PM 40.20 -74.50 380 36000
08:17PM 40.18 -74.63 365 36000
08:18PM 40.18 -74.77 365 19400
08:19PM 40.17 -74.90 372 21800
08:20PM 40.17 -75.03 372 24200
08:21PM 40.15 -75.17 385 25500
08:22PM 40.13 -75.33 430 26400
What would cause that and what effect would it have on passengers?
Or is there some other explanation?

Hope someone can elighten me


Not so much a massive loss of altitude, but phantom gain of altitude. This looks like a normal climb- however, for some reason the FAA system did not get the altitude on a few of the track points. In these cases, the flight plan alt is given, hence a “jump” to FL360 then a “drop” back to actual.

This can be caused by multiple radar sites reporting the track.

Welcome the FlightAware!


Thank you for explaining that to me. I will be flying that route in November and was dreading a similar thing happening!!
I also appreciate your welcome.