If one is able to get an anti-aircraft missile on the scene of an accident in time to intercept HRH (and know that he's the pilot at the time, etc. etc.), then one can probably get that missile in position to shoot him while he's at home, or at the palace, or doing any kind of charity work.
Why all the fuss?
'These people want sensationalism, so what could possibly be more repugnant to the British people than a suicide bomber at a hospital helipad taking out the second in line to the throne, the second pilot, the doctor, the paramedics, the patient, the hospital staff and the fire crew!
As mister bonkers says, 'all you have to do is sit at the gate and watch for who is on crew' .... Meanwhile the rest of the paradise seekers are hanging around the regions hospitals ready to do the deed.
But as someone said earlier, all this has been taken into account.