The US form isn't available online, you have to obtain it and complete it at the airport. In PHX, this means giving yourself up to an hour extra time, as the GA finding the form isn't always the swiftest process, and the TSA can be very obtuse when it comes to examining the case.
From their site:
"US Airways will allow passengers to transport firearms in accordance with Federal Law.
Items of shooting equipment will be accepted as checked baggage only.
A passenger who presents checked baggage that contains a firearm must declare the weapon and sign a written acknowledgement that the firearm is unloaded.
Firearms must be packed in a manufacturer’s hard–sided container specifically designed for the firearm, a locked hard–sided gun case, or a locked hard–sided piece of luggage. Handguns may be packed in a locked hard–sided gun case, and then packed inside an unlocked soft–sided piece of luggage. However, a Conditional Acceptance Tag must be used in this case.
Baggage containing firearms must be locked at all times and the key or lock combination retained by the passenger.
A Firearm Unloaded Declaration form (available only at the airport) must be signed and placed inside the bag or gun case.
Checked ammunition may not exceed 11 lbs/5 kg per person. Ammunition clips with ammunition loaded are not accepted. Ammunition must be packed in the original manufacturing package or constructed of wood, fiber, plastic, or metal and provide separation for cartridges. Ammunition may be checked in the same piece of luggage as a firearm. No additional documentation is required.
There is no limit to the number of items contained in rifle, shotgun or pistol case, up to 50 lbs/23 kg, 62 in/157 cm in maximum.
A passenger who presents a firearm to be checked to an international destination must be in possession of all required import documentation for their international destination city and any international transit points. It is the responsibility of the passenger to acquire the required documentation from the applicable government entity prior to travel (usually a consulate or embassy). Firearms will not be accepted for transport if international import requirements have not been met."
Images from older, completed forms online:
http://www.arkansascarry.com/uploads...rways_back.jpg
and
http://thegunzone.com/images/declarationform.jpg