Today, it is precisely 13 years since a nutbag islamist on board United 93 switched off his transponder and caused problems for ATC tracking staff.
Earlier this year, the same appears to have happened to MH370.
I have heard various excuses varying between "far fetched" and "daft" for why this switch should not be capable of being disabled from the flight deck. Will the regulators ever wake up?
If they do, they could also consider why FDR and CVR batteries are so inadequate and why these should not operate in passive transponder mode.