It's a risk in a quarry where they have blasting caps - the RF can set off a detonator (so I'm told - never tried it, not even in my misspent yoof).
If the 100 watts or more of pulsed RF from the transponder don't cause an aircraft to explode, the few watts from the mobile phone aren't likely to do so, either. Especially since the signal strength reduces proportional to the square of the distance.
But such "risks" are the sort of story dreamed up by officious officials to justify their rulemaking.
There are folks in this world who are horrified by the thought that someone, somewhere, may be having fun - and they will invent rules as fast as they can go to change all that.
Have you had such an experience?
Maybe you need a copy of some learned scientific sheet on field strengths etc?