I'm flying from Italy to Australia with Cathay Pacific. Can I take my spearfishing gun, and other free-diving equipment with me as luggage?
Since Cathay is HK ailines and all planes are registered in HK, so they follow HK law.
Based on HK Law (Firearms And Ammunition Ordnance), spearfishing gun is arm. The Sect 2 of the ordinance consider any harpoon or spear gun, however powered or size, as arm. However the law does not rule the ammunition of spearfishing gun.
Base on sect 8, you may take spearfishing gun on CX flight if you stay in restricted area. However, the items should be put in checked luggage, and also HK customs may ask you official certificate which you are allowed to own spearfishing gun in both departure and arrival countries.
There is no other specific rules related to carry general diving equipment on flight in HK, except gas tank and arms.
Yes, you can, but the spear gun can only be taken in checked-in luggage. First, while not a firearm it's a projectile weapon nevertheless, and all airports forbid carrying such on board in carry-on baggage or on person. Second, TSA seems to consider spear guns as sporting goods that can be used as bludgeons.
More info on TSA website