I can really only think of one scenario where a plane completely disappears from radar and then existence without any mayday call.
It involves either a surface to air missile, an air to air missile, or a bomb smuggled on board somehow.
if it were the latter, I think someone would have claimed credit for there successful terrorist act by now. If it were the former, I think the responsible government would be very carefully covering things up.
:: It involves either a surface to air missile, an air to air missile, or a bomb smuggled on board somehow. ::
The first two in your list are also known as “center fuel tank spark from loose wiring”
If it was a successful bombing, there is an explanation for why no credit has been claimed. It was just a trial run, a proof of concept. Let's say, for example, they have coopted the night shift at a Pakistani shaving cream factory, and have managed to load bombs into perfect metal cans of shaving cream. They might have dozens of them, but they need to prove that they will take down an airliner.
If that is the case, now they know, but we don't know.
So on a given day, 20 jihadists board aircraft, with very simple instructions: make sure that your shaving cream can bomb is in the air at noon GMT on a certain day.
This concept would be similar to the thwarted "Operation Bojinko" from circa 2000. The goal is to blow up a dozen or more jetliners over the ocean at the same time.
Like the first and second World Trade Center bombings indicate, these guys don't quit, they try again.
Oh that’s right, it could have been a mistake. What was that one case where the Navy was practicing and they accidentally shot down a passenger plane? Was that the US? I vaguely remember something like that. That wasn’t covered up though.