Heard today 4/13 after on UA804 after takeoff from SIN. $AL is not UA bit some other US airline... I'll refer to it as XXnnn here to protect the (innocent|guilty). No XX is not the airline code either :-)
The whole exchange is paraphrased (I had no paper/pen to write it down there and then)
Singapore Control: XXNnn, Singapore Control.. do you have ADS-B?
XXXnnn: Singapore Control, say again?
Singapore Control: XXNnn, ADS-B (repeats a few times, changing pronounciation apparently for clarity). [ does not explain what it is though ]
XXNnn: XXnnn What is that? I don't know what that is
Singapore Control: XXnnn: in that case I have to ask you to descend from FL310 to FL270
XXXnnn: Singapore Control, We're looking, we're checking
[few minutes wait]
XXXNnn: Singapore Control, XXXnnn: We could not find it. What was that level you wanted us to descend to? 270 right?
Singapore Control: XXXnnn descend to FL270
...
a bit later Singapore Control queries XXXnnn again, asking for their level, no answer, so query is relayed through a different plane. XXXnnn answers they are still in the descend.
What reason could there be for Singapore Control to only allow XXXnnn FL310 if they have ADS-B and require them to FL270 otherwise?
Besides that, after all the explanations about airline systems in the wake of MH370, how can the pilots of an americal airline flying internationally not know what ADS-B is (and not find it in their documentation either)? Is it that rare?
On the same flight, Singapore Control had a few problens raising UA896 a few times and asked our flight UA804 to try and reach them. UA804 replied they think they switched frequency already. Some minutes (10-15?) later contact was apparently restored..