"UPDATE - Monday, March 17, 2014 - 12:15 PM EST Some have raised the statement that TCAS doesn’t work if the transponder is disabled… this is only partially correct. Other planes TCAS would NOT see MH370 at all. MH370 would not actively query other planes as it’s transponder is off HOWEVER it could still listen to any transponder output from other planes that are actively transmitting. SQ68 would have been actively transmitting while in-range of Subang ATC center.

Even if TCAS on MH370 wasn’t working for some reason, an in-expensive portable ADS-B receiver paired with an iPad and Foreflight app would allow a pilot to receive the ADS-B output being transmitted by SQ68 at that time."