Traveling with scuba gear is challenging at best. It's heavy, bulky, and some of it is delicate. You generally want to keep your dive computer and certain other pieces of valuable or fragile equipment in your carry-on, but the TSA can and will confiscate anything they deem to be suspicious. Here are some things you can do to ensure your TSA encounter goes smoothly, so you can exit the security checkpoint with all your gear intact.
TSA screening is simply a fact of life if you need to fly. Nobody likes having to endure the added delay and hassle, but it's not hard to keep your TSA screening short and uneventful.
1. First and most importantly, keep a positive attitude.
TSA agents are dealing with travelers who resent them all day, every day. Even if you're running late or feel stressed for other reasons, make an effort to present a cheerful and helpful face to the agents at the security checkpoint. Wherever a rule is open to interpretation or the agent's own judgment, it's more likely to go your way if you've made a good impression.
2. Keep carry-on gear to the absolute minimum.
Every piece of gear in your carry-on is a potential problem for the TSA. Your regulator, octo, BCD and most other equipment can go into a checked bag that's carefully packed to ensure everything is adequately padded. Many divers will wrap their reg and octo inside their wetsuit, place that bundle in the center of the bag, and then brace it on either side with their fins. Using fins for extra protection and support inside the bag is even more important if your checked bag is soft-sided. Your mask may have come in a box, but even if it didn't, it's not hard to find a rigid plastic box of sufficient size that will keep it protected as your bag runs the baggage handler gauntlet.
3. Remember that diving knives, spearguns and extra spears are all items that MUST go into a checked bag.
Any item that could be used as a weapon is prohibited inside the airplane cabin, and that goes for purpose-built scuba gear, too. You may wince when you put that pricey new dive knife into a bag you intend to check, worried that it may be stolen, but if you attempt to take the knife through a TSA checkpoint it will definitely be confiscated. Whatever it is, if it's sharp or pointy, plan on putting it in a checked bag.
4. Bring the manufacturer manuals or user guides for carry-on gear that will be unfamiliar to non-divers.
Many a traveling diver has had his dive computer, regulator or rechargeable battery pack confiscated simply because the TSA agent had no idea what they were and erred on the side of caution---as the TSA agents are supposed to do. Be prepared to show the TSA agent your scuba certification card and the pages in the manual(s) or user guide(s) that show a picture of the gear. If possible, bring a dive magazine that contains an illustrated ad for the equipment. Bookmark or dog-ear the relevant pages ahead of time so you can flip to them quickly.
Most user guides or manuals will have a picture at the front at least, with all parts of the piece of equipment labeled. Even if the security agent speaks a different language, the manual, guide or magazine ad will demonstrate that your dive computer is not some kind of homemade explosive timer device but a mass-produced, commercially-available piece of dive equipment. Similarly, if you've decided you prefer to carry your reg in your carry-on bag, your documentation will help prove it's not a gas mask.
If you've misplaced the original user guides or manuals, you can often download new copies from the manufacturer website in PDF format, then print out a hard copy. If the manufacturer doesn't make copies available online, contact them to inquire about having copies mailed to you well in advance of your trip.
5. Assume the security agent will question any piece of dive gear that would be unfamiliar to non-divers.
Remove the possibly unfamiliar items and let them go through the checkpoint in their own, separate bins. First, this demonstrates that you are not trying to hide them. Second, if the agent has any questions you won't have to dig through your carry-on to pull the equipment out for the agent's inspection.
As in most of life and all of travel, when preparing to deal with airport security it's best to hope for the best, but plan for the worst.