LordSpandexMasher wrote:-
There isn't a solution.
Yes there is:-
1. Vastly enhance current aircraft control systems so that they simply refuse deliberate control inputs by a pilot in charge that could only have the intent of crashing the aircraft. This would include obvious things that seem to not currently exist such as auto pilots also knowing about the height of all terrain and high buildings or masts etc on the ground so they would never accept any flight route that would fly the airplane deliberately in to terrain. The aircraft should only be capable of being descended to anywhere near ground level at locations where there are known suitable airports of an adequate minimum runway length for that aircraft type.
2. As part of that vast enhancement in auto pilot systems also require that all commercial passenger aircraft over 40 seats or whatever figure is decided on (it is probably going to be too expensive to retrofit and/or fit at all these kinds of protections for very small scheduled passenger aircraft) have a capability where the flight controls on the flight deck can be locked out from the pilot in charge and an auto land sequence to land the aircraft at the nearest commercial airport with a long off runway be initiated remotely by either the nearest ATC centre or the airline's own operations and control centre.
3. In order to facilitate the use of the remote auto land facility at point 2 above ensure that there are various prominently marked emergency telephones in break glass type cabinets in the passenger cabin (with a suitable threat of an up to 10,000 Euro fine or up to 6 months in jail for inappropriate or malicious use) and galley areas that either cabin crew or passengers can use to contact ATC or the airline base in an emergency to demand that control be taken out of the hands of the flight deck crew right now and the plane auto landed at the nearest suitable airport in terms of runway length and current weather conditions.
None of this can be done overnight but it could be designed in to all new builds within may be two years and retro fitted to all aircraft still flying within five years if they still have at least five years expected remaining use as a commercial aircraft ahead of them at that point in time. So in ten years we might actually be fully protected against such a possible event in all but very small passenger airplanes (which only carry a tiny percentage of total passenger numbers and passenger hours flown) will probably not have such protection because it is not economically viable (although it may become so in the fullness of time such as another 25 years from now)
At this point a pilot in charge could then only crash the airplane by carrying on materials that would let him set fire to the flight deck or similar but in principle security checks for getting airside also ought to prevent any pilot from being able to do that.
With the current state of computer automation it surely can be done if the threat is perceived to be large and significant enough and there is also the political will to force the manufacturers and the airlines to do it.