Cat S sounds like an elistist "teacher" that trusts no one but himself with lethal force. When faced with a dedicated suicidal terrorist trying to break down my cockpit door, I'll take my chances with miniscule possibility of an accidental discharge. As a matter of practicality, flightdeck firearms should be aircraft equipment kept in quick reaction safes at each pilot position. In practice, they'd never be touched except by armourers during B checks or in the case of a terrorist breaking through the cockpit door to commandeer the aircraft. It's the last defense after all the bureaucrats and airline executives have failed. This is a no brainer to anyone capable of weighing risk/reward, critical thinking, and without a blind ajenda.