The aircraft wouldn't have to lose very much height at that distance before it dropped below the radar horizon for a land based radar site at 200Nm out. Nevertheless, I'm confused - why can they not say 'it was travelling at [x] knots on vector [y] at rate of descent [z] before it vanished from our scopes'? That's what military radar installations are there for, surely?
My AAA Radar consist of two systems a active search radar which goes in flat terrain in a 360 degrees view from zero to 25nm. So i have a capability to detect any moving subject within this dome of 25nm around my radar. I have coupled to this a tracking radar which allows me to track a specific subject up to 25nm. This is a very powerful radar. I can track down a bike driving inside the 25nm dome, if i like to.
Every radar has a dome it can scan. But i bet none of the search radar installations is directly sitting at the coast of MY or VN. So 200nm could be just not enough.
I personally would not see any reason why a level change would make the aircraft disappear from radar screen.
I don't think an AWACS or Sentry was in the airspace. I don't see any US carrier activity in that area. This could have been an advantage
