I do believe that if airline pilots were armed, they should be sent to a school to learn to safely use it. Quite frankly, I believe that anyone with a weapon should learn to safely use a weapon. Anyone who holds a weapon of any kind should be accurate and intelligent with it.
Airline pilots should learn how to use weapons if they are allowed to be armed. Just like officers are trained to use their weapons, so should airline pilots be trained to use them if they are allowed to carry weapons. I believe that is a good idea because the last thing I would want is a airline pilot with no weapon training during a hijacker event. Plus, I would not want to be shot because the pilot did not know how to use the weapon.
If airline pilots were armed in the sky, they should have to attend a mandatory safety class in order to have this weapon then. Pilots have a huge responsibility for the safety of there passengers and if they were armed and trained then they could also defend the passengers in a terrorist effort to hijack the plane. If only one person has a gun, it is a huge power imbalance rather than giving both people guns and leveling the playing field.
I believe that pilots should be armed on one hundred percent of flights. This would stop all terrorist attacks. I also believe that the airlines should be responsible enough to train their pilots in proper gun usage. If any airline ever did both these things I would always choose them as it would make me feel the most safe.