I'm planning some travel . . Toronto Canada to the US . . with a Phantom4 and been researching US and Canadian rules & regs. For my part, I will only take my UAV with me as carry-on ( although you can check it as long as batteries are removed. Some UAV forum recommend putting blades in your checked baggage especially if they are carbon fiber since they "could be used as a weapon". Not long ago, I had a small Braun coffee grinder taken away from me by Toronto airport security "because it had blades" in it . . 2 rounded metal 1 inch blades in the bottom of a plastic cylinder. . . no sense arguing, but I'll put them in checked baggage, just to save the hassle. I'm still trying to find a good hard sided case that meets the dimensions spec. Size/weight limits are similar for most airlines (but not identical). This is what Canada and United Airlines say re: carry-on.
Lithium Batteries - LiPo
Both Air Canada and United Airlines allow multiple (2-3+) <100watt hr batteries but ONLY in carry-on. They must be separated from the device, labeled and terminals taped over. The P4 battery is 81.3w fully charged and they recommend <50% SoC ( State of Charge). volts x AmpHr = Watts. For Phantom 4 it's 15.2 x 5.35 (5350mAh) = 81.3W. It's all here on the dji website if the security guys want you to show them. The charging terminals should be taped over so they cannot touch anything metallic by accident. I recommend that Blue paint edging tape. It's an obvious colour and can be pulled off and reused without leaving sticky residue on the battery.
Regulations say multiple spare batteries can only be for personal use ( ie as long as they are not for resale). I'm also putting my 2 spares in a fireproof safety bag ( get them at most hobby places). With a recommended safety label on the outside of the fireproof bag you have a much better chance there will be fewer questions (or ANY questions) as you go through security. if you look/act like a safety minded person and you get treated better I find. You can just copy/print this label below or make one yourself. The controller battery is not easily removable so I guess that just stays in the case. With a charged LiPo battery installed it's illegal to go in checked baggage.
It says on the FAA website the "aircraft" needs to be registered. For US citizens it's an actual registration number like all piloted planes. You can do that on line if it is less than 55lbs. P4 is only 3 lbs .. . . but if you are a foreigner ( like Canadian) you still have to register as "proof of ownership". There are 2 wrinkles here for Canadians.
First, you can only register online from INSIDE the USA. The FAA website says they will refuse to allow you to the registration page if it sees a foreign IP address. . . it's true, I tried. Not sure how you do that unless you wait till you arrive and then register on line, so I haven't seen the questions or forms they ask for.
And second, you cannot do any work with it in the US. If it's for commercial purposes then it must be registered and there is another whole layer of forms about work permits and VISAs. I'm just going for a holiday to visit family and do photos and videos, so that should be ok. I live just a couple of miles from the border in Canada so I went over to US Customs this morning to talk to a customs officer directly and I got a pretty senior looking officer who was very helpful. He told me basically "no problem" after we had discussed pretty much everything I just outlined here above. He did not know about the FAA rules specifically though.
HAVE FUN . . . no working allowed!