5. A pilot might be mentally unstable and should not be trusted with something so dangerous as a gun.
4. What if the gun snuck out of its holster while the pilot was busy and shot someone?
3. A flight atttendant might see a gun in the pilot's pocket and mistakenly believe he is sexually aroused, resulting in a case of sexual harrassment.
2. Recognizing an old friend, a passenger might say, "HI, Jack!", and be shot on the spot.
AND THE NUMBER ONE REASON CANADIAN PILOTS WON'T CARRY GUNS:
1. PILOTS MIGHT HIJACK THEMSELVES TO CUBA!