Yes, if the airline pilots had been armed, the terrorist attacks on 9/11 would have turned out differently, because the people would have been able to fight for their lives. The airline pilots at least could have fought back, and the gun is a good equalizer, even if there are multiple terrorists on board.
I think that had the airline pilots had been armed, the terrorist attacks on 9/11 would have turned out differently. I think that if the pilots were armed, those thinking of hijacking the plane would not have been able to take over the plane so easily. They should have probably thought of a different type of attack.
The pilots being armed would have changed the outcome of the 9/11 attacks because the playing ground would have been level as a result of the pilot having a handgun. The pilot could have been warned about a possible terrorist hijacking from the flight attendant, and this would have triggered him to arm himself to guard the controls to the aircraft. It certainly would have helped 9/11 turn out different than it did.
While we will never know what would have happened I believe there would have been a strong chance that the pilots may have been able to succeed in killing the terrorists and preventing 9/11 to begin with, I think airline pilots should be armed and trained to use the firearm with deadly accuracy.