4 questions about missing Malaysian plane answered

She asked: "Why was the transponder switched off?''

A: Investigators have not categorically said the transponder was shut off deliberately, allowing for the possibility that it malfunctioned or was damaged in an explosion or some other incident. But there are strong grounds to think that someone on board did switch it off. The most obvious reason why a pilot would turn off the transponder is to make their plane invisible to commercial radar or other nearby planes. This would be consistent with the actions of someone on board who wanted to make it hard for anyone to track where the plane was headed, and strengthens suspicion of foul play. It would be very rare for a pilot to turn off the transponder in midair, though if it were malfunctioning they might do that.

Yip Royal, 29, a Hong Kong man at Tokyo's Haneda Airport.