A 20 Million Dollar plane that can be turned off by flipping a switch? No such thing exists.
The United States imposed sanctions on Pakistan in 1989/90 under the Pressler Amendment. At that time, the PAF operated two fully fledged squadrons of F-16s. If there was such a thing as a kill switch, or if there were a way to stop our F-16s from performing operational tasks, why did they bother going through years of sanctions and spare parts restrictions etc? They could have just as easily grounded our entire fleet and we wouldn't have been able to do anything about it. Despite this, throughout the 90s, the PAF conducted regular operations with those F-16s, took part in fire demonstrations, conducted exercises and on and on.
Not only Pakistan, but the Iranian Air Force too used their F-14 Tomcats until they had absolutely no way of repairing them, at which point they took them apart for reverse engineering. Why the heck would the United States not flip the "kill switch" on them, and drop them out of the skies?
The kind of mechanism being talked about is very much possible. Not just possible, it a very simple thing. Even I can make one provided I get access to satellite links. The Americans have them though.
Americans have satellite technology, no doubt. They may even be able to embed some sort of critical shutdown deep inside their aircraft, but you can't transmit a signal to a satellite using an piece of technology embedded deep within the aircraft without it being detected, unless you assume that the people operating the aircraft are completely illiterate. If a kill switch existed deep within every aircraft, someone would have to manually flip it, which defeats the purpose of such a system. Also, all electronic systems within an aircraft can be replaced or, in dire circumstances (which is what War is), hacked. If Pakistan ever went to War with the US, I doubt we would still consider ourselves bound by contract to not reverse engineer the aircraft.
But, for the sake of argument, let's assume this could be possible technologically. It would still be impossible to implement in the practical world. The defence industry is the largest source of foreign income for the United States. If any such "kill switch" is detected in
any one of their products, the entire industry will collapse within a matter of months. If the PAF, for example, even smelled that the aircraft could be turned off remotely, they would never buy it. If India even got a sniff of something of this sort, Lockheed Martin and Boeing could kiss the $10 Billion MMRCA goodbye. The United Kingdom, Italy, the Netherlands, Canada, Turkey, Australia, Norway, Denmark, Saudi Arabia, the United Arab Emirates, Japan, Brazil, and so many more countries around the world would never,
ever procure another piece of defence technology from the US if this were even
remotely true. This would be more disastrous for the US than any possible War they could get involved in today.
In other words, America's economy is directly linked with the well being of their defence indusry, and any move that would bring the industry down would be disastrous for the US. The United States would rather go to war against Pakistan's handful of F-16s than pay a huge economic price for building such a mechanism inside every, or even some, weapon system. Of course, that's assuming it is technically possible to hide something like this from the operator until the last minute, which isn't the case.