Yes. In case of a terroristic threat on their plane, they need to be able to protect their plane and there passenger's. A typical standard police issue 9mm would be sufficient for all pilots. All pilots would need to have small firearms training so the pilot knows ow the firearm works.
Added: It is NOT a mtter of 'should' they, this question is not open to a debate. It is established law that commercial airline pilots CAN, when properly trained, carry firearms in the cockpit.
Which helicopter pilots?
No. All firearms should be registered or licensed to a responsible holder to avoid accident or illegal discharge.
From what i see,they only seem to carry a sword.
No
No. Cannot carry, touch, shoot, or have access to firearms.
US pilots usually carry the Beretta M-9, 9mm
No. Most correctional officers do not carry firearms.
Yes
Each branch of the military and each branch of many federal agencies carry firearms and train with firearms. The IRS has agents that carry firearms. Probably the largest users would be the Marines and Army.
The same authority that enables them to carry firearms.
to beat people up
Depends on the laws of the jurisdiction which you are in.