Asterix and Yellow Tim are both correct. But that points even more towards the likelihood that the plane has just crashed into the sea somewhere without anyone knowing for sure. Even the intelligence services are not completely callous and indifferent to the fate of hundreds of people and indirect ways would be found to alert those who need to know without endagering the source, if the aircraft was known to have been taken anywhere or had if its wreckage had been spotted, even via some secret system or a known system whose complete capabilities are secret. What this disaster shows, if nothing else, is that surveillance might be everywhere in some form or other but it's a long way from comprehensive and omniscient.