This truly was "Nightmare at 10,000 Feet" - so sorry to hear about this. I'll bet you loaded up your DX before travel (to have something to read) and it waited until the idle time during boarding & take-off to decide to index the lot!
I don't know of any way to turn off the indexing function. I would try shutting it off and when it restarted, trying to open something to read before it could start the indexing. Yikes! I truly feel your pain.
