Also, the baseband processor in most phones runs its own code out of the control of the OS and has access to a ton of surprising stuff.
Also you asked if carriers need a backdoor, which I answered: "Wouldn't that need a backdoor in the OS's GPS software/driver?"
PS asking a question and berating any answer you don't like is not exactly optimal strategy for getting people to answer your future questions.
In airplane mode it _shouldn't_ be sending that data.
With aGPS, the cell phones can download up to date GPS almanac from the tower instead of having to lock to GPS satellites to get it.
The parent commenter explicitly write "A-GPS which uses triangulation".
That is simply not true.
The BTS (cell tower) will broadcast the connection info about neighbouring towers and your device will report back the signal strength for each. The network can then make a decision if it needs to move you. This is known as Mobile Assisted Hand Over.
The aim of the game here is maximising signal quality, which is not necessary the same as minimising position to a tower.