Among the most ridiculous notions, in my mind:
- That the schemers would thread a ridge-hugging route through the mountains at night so they could land and hold the airplane hostage, with the supposed reasons for this changing by the hour;
- That they could keep an entire planeload of electronics-toting passengers silent as the plane flew over populated territories, including any pax with handheld satellite phones;
- That the early, wild flight maneuvers soon after MH370 left its standard course were an attempt to evade radar; or
- That the plane landed in a well-populated area but was hidden in a massive cover-up.
If the flight data recorder is ever found and recovered, we'll find out a lot. (It's possible that the voice recorder (CVR) may have been overwritten, though, if the aircraft continued for seven hours after whatever weird event took it from its course.)
Skeptics are free to criticize the "system failure" notion, but should acknowledge that the 777 for all its virtues has not been perfect, the failure of a navigational core unit on a Malaysia Air flight in 2005 (the ADIRU) being one example. In that case, an apparently impossible combination of events came very close to crashing the plane. Yes, Boeing has ordered thorough precautions against a repeat, but what other gremlins lie in wait?
With thorough flight automation, unfortunately, also comes the possibility of rare but terrifying failures.