Regarding radar coverage, either military or civil, you can bet your bottom dollar that Singapore would have information that they would not make public, ever.
SLFplatine asked about FDR/CVR being ejectable, yes of course they can and Martin Baker, if asked would be happy to produce a unit that under pre set conditions would eject from the aircraft and float. Now the problems, it would have to be a removable self contained unit as regulatory authorities would require a function test now and then, so spare units would be needed and a test rig would be needed, (possibly run by MB), the zeros behind the $ sign just get longer! A unit located in the horizontal stabilizer, designed to eject at an angle, so avoiding fouling the sinking wreckage, which may, by now, be inverted, should suffice, these days many of the electronic boxes are connected via multi pin bayonet type connectors and secured by conventional means to prevent the unit vibrating or being shaken out, back to Martin Baker who specialise in perfecting systems where conventional securing can be breached when required.
Short answer, yes, an ejectable and floating CVR/FDR is quite feasible.