Originally Posted by
jmmilner
With such a device it becomes possible to count aircraft pressurization cycles so one could set the device to wait for the descent prior to landing, wait 30 minutes after reaching maximum cabin altitude, or even delay 5 or 10 flight legs before triggering. The only practical limit is how long the device remains undetected in the aircraft.
Anybody counting on technical complexity to prevent a device being made by terrorists is making a bad bet.
My point is not that technical complexity of such a job is beyond the reach of a modern day terrorist, it's mainly that, in this situation, cooking up functional remote detonation is what Russians call "having sex while standing in a hammock": enduring difficulties for the sake of enduring difficulties. Unless the terrorist group has access to off-the-shelf remote detonators that can work at a range of 10+ km, can punch through the Faraday cage of the fuselage, and can function despite the Doppler shift due to 400 kt speed difference between the transmitter and the receiver, it's hard to see them going to the effort of making one from scratch, when the job can easily be done with a timer.
One other possibility is to make a device that can be accessed remotely via the onboard Wi-Fi, but even that is a challenge.