Correct. For international arrivals into the US, movement between cabins is prohibited by DHS and it is up to the cabin crew to enforce and for the carrier to be penalized if derelict.

But, that is barely, if ever, enforced. If cabin crew do intervene, don't get into a tussle about it. DHS does do random inspections and if there is one aboard, you may find the crew sticking obsessively to the rules. Same thing if one of their colleagues was "busted" recently.

This is truly rarely enforced, so not something to obsess on.

I often walk the entire length of the plane and back. Never an issue.

I am not privy to the rules, but have two anecdotes in the last 2 months which would seem to support the "barely, if ever enforced" part of your comment.

Flew HKG-JFK and HKG-LAX, both in F. In the JFK sector, a couple in 2K and 2D must've gone to the back 3-4 times in the first few hours of the flight. I went to sleep for the rest but am guessing they might've done more after I was sleeping.

On the LAX sector, the first 3+ hours were probably the worst I've ever had on CX F. A family of 5 (2 grandparents, 2 parents 1 young child ~2 years old) booked 2 F seats and 3 J seats. They started the flight with the child in 2D and grandmother in 2K. The child was doing some screaming and also being calm at times, but no matter what the 3 adults in back were nonstop cycling up to the F cabin, giving the grandmother tips and advice on how to deal with the kid, etc. Just constant coming through the cabin up from J. Basically a party with a rotating cast of characters - usually coming up from behind the curtain - in the F cabin huddled around 2D. Totally surreal I'd never seen such a blatant violation of the F cabin integrity on CX before. I was sitting in 2A and wasn't thrilled during dinner (cx882) given the rotating personnel, noisy party that kept happening at 2D; as I intended to nod off after dinner, I finally told the cabin crew how absurd I thought this situation was and to please fix it. The SP ended up talking to the passengers huddling around 2D a few minutes later: the ultimate solution was for the child and grandmother to go to J, and the grandfather to come to F, and they left an empty F seat! Translation: 3 J seats now had 4 passengers including a child used to a serious amount of attention and doting, and 2 F seats now had 1!

I can't be sure if this child was an infant or not, but I never saw her again the rest of the flight. Anyway my point of the story is those J passengers must really have not been thrilled at all. This was probably the most clueless / bizarre kid/parent situation I'd ever seen on a CX flight, and they joined the J cabin right around 8pm HK time....when you go to bed on that flight.

The OP didn't ask for your opinion on booking his/her parents in J. If you have something to contribute to the discussion about the ability to visit someone in J when you're seated in F, then go for it. But to judge the OP for booking them in J, while making a few assumptions along the way, is totally unnecessary.

Only 1 seat is available in F? My parents wont take upgrades (paid or miles or comp) for 1.

How do they treat the PEY cabin then? Problem with PEY is on some planes, there are no lavs for PEY and thus PEY has to go back to the Y cabin to use the lavs.

Especially checking on older parents and not just boozy mates.

I have not heard of such regulation, but on every CX flight to the US, it is stated clearly over the PA that 'congregating in galleys and other areas of the aircraft is prohibited'. And yes, the FAs do enforce it.

Whether an F pax visiting a J pax and hanging around is considered 'congregating', well...

Nor does your scolding, Enigma368. I actually thought that FlyingHighAgain's comment was intended to be, and was, a friendly and lighthearted comment which made me smile. Relax, take a breath.

I usually fly in J and hubby flies in Y. I often go back to say hi during the flight. We've even swapped seats on occasion (when he had a bad leg and we swapped half way through the flight). On that time, they said one swap was ok, but not multiple swaps (ie lots of back and forth). Seemed fair enough.

Why in the world didn't the grandmother stay in FC after the seat swap? She obviously wasn't good at handling the kid, so what was the point of her moving back and wasting a FC ticket?

Absolutely no idea whatsoever.

It was the most out of control situation I've ever experienced in F. More surprising was the crew tolerated it for 4+ hours until I voiced my displeasure.

Could the family have been celebrities of some sort in Hong Kong? Often in such cases, crew prefer not to enforce any rules. In fact, was the FC cabin full, so that if they attempted to purchase five tickets close to departure, there weren't enough seats available in FC for the entire group?

Why wait four hours! 10 minutes is normally my limit before getting the crew involved.

Yep. On a recent flight in F, I was in 2A, the husband of an op up pax in 1D kept coming up through my aisle. Raised my voice ever so slightly in a quick note to the FP and things were taken care of immediately with utmost professionalism. (as usual, I love CX crew!)