“Here, every blip on the screen is suspicious because that’s the way we live. That’s our daily program. I can’t imagine they pay as much attention, but if a blip runs wide or runs strange, I would expect them to notice.”
Someone on another thread posted a link to a theory that the missing 777 used SIA68 (Singapore Airlines flight 68) to cloak their own airplane until they could get across the Indian Ocean, away from primary radar.
http://keithledgerwood.tumblr.com/post/79838944823/did-malaysian-airlines-370-disappear-using-sia68-sq68
I like this theory, generally speaking, without having plotted it out completely on the charts myself. I looked at FlightRadar24.com, plugged in a playback for 1720z on the 7th, and sure enough SIA68 is just approaching overhead Kuala Lumpur, at 502 knots and 30k. So according to this theory the plot of their radar track nearly coincided with SIA68's path sometime later, since MH370 turned west on a convergent path at the same time. MH370 was able to join up with them all the way across the Indian Ocean, to an undisclosed location.
I don't know if SIA68 was the host, the cloaking aircraft, since there are many other 777s in the same direction, and I don't agree that TCAS will work in a receive mode without giving away position, but otherwise I like this theory better that most others.
Incidentally a big airplane will paint on onboard weather radar at 25 miles, and emits only a very weak signal. They could have used this to help acquire a visual on another 777, after using a portable ADS-B receiver to find a suitable host airplane, much like flightradar24.com uses ADS-B data for their detailed displays.
http://ipadpilotnews.com/2013/04/portable-ads-b-receiver-buyers-guide/