A quick one. I just hit on this interesting idea from blogger Keith Ledgerwood: http://keithledgerwood.tumblr.com/post/79838944823/did-malaysian-airlines-370-disappear-using-sia68.
To summarise: SIA was in the area at the time MH370 was there. The crew of MH370 deactivated the transponder but would have known of the whereabouts of SIA68. It would have to have been a visual tailchase but if the two aircraft were close, the radar return could be a single paint, squawking the SIA68 B777’s transponder signature. That is, MH370 would have been invisible to radar as it tracked along SIA68’s flight path northwest. The TCAS system fitted to all airliners to warn of the proximity of other aircraft works on the transmissions from the transponder but MH370 had switched the transponder off so SIA68 would have no idea that MH370 was behind it, hiding in its shadow.
After looking at all the details, it is my opinion that MH370 snuck out of the Bay of Bengal using SIA68 as the perfect cover. It entered radar coverage already in the radar shadow of the other 777, stayed there throughout coverage, and then exited SIA68’s shadow and then most likely landed in one of several land locations north of India and Afghanistan.
Here is a timeline from UK Channel 4: