Why Can Transponders Be Turned Off?
Tuesday, 18 March 2014 | by Pat's Picks

Since the disappearance of Malaysia Airlines Flight 370, one of the thoughts I’ve had is why a transponder can be turned off in the first place. Gregg Easterbrook writes an Op-Ed in the New York Times asking the same question. He says transponders should have been re-engineered after the September 11th attacks so they could not be manually turned off. Only a hijacker would want to turn off a transponder.
SOURCE: New York Times