fs once and for all..
There are essentially four common types of ATC surveillance. Primary radar requires a return off the skin of the aeroplane = heaps of power out for a tiny reflected return = very limited range (< 100 nm). All other forms of surveillance (secondary radar/ADS-Broadcast/ADS-Contract) require a transponder in the aeroplane in order to get s return. SSR and ADS-B are ground based, so they are limited by line-of-sight rules (i.e range ~ 300nm), ADS-C is via satellite return and has essentially world wide coverage. No return on anything except Primary simply means the transponder is u/s
Right. Now, the question becomes: what primary radar ATC stations are there along the route of MH370, and what were their actual effective ranges? And, when newspapers say that the plane disappeared from the radars, do they mean that the primary return was lost, or that the transponder had stopped transmitting and the primary return wasn't there to begin with?
The possible glide distance would be approximately 20 times the altitude, hence about 20*6 = 120 miles but not at that speed, to achieve this maximum glide distance pilots would have to lower the speed.
OK, good to know - 120 miles is not a lot but would probably take the aircraft out of the search area.