How to avoid Aircraft swaps? A380 to 77W without First
 

Thai Airways are notoriously known for their frequent aircraft swaps.

I'm currently booked on TG910 BKK-LHR in First on January 7th next year. To my understanding they have a tendency to swap aircraft quite frequently, and the LHR and FRA routes are usually quite badly affected whereas the CDG route rarely seems to get its A380 swapped for a 777-300ER.

Since the travel is in the first week of January which is a popular travel period, are Thai less likely to substitute the A380 for a 777-300ER on the LHR route, or should I rebook myself to CDG just to be on the safe side? It's nearly a year out, so I understand that a lot can happen in that time.

I've checked my crystal balls (both of them) but there's no way of knowing I'm afraid

Easy. Fly on a different airline.

No way of knowing for sure sadly - but given it is almost a year into the future, the entire fleet should be back in action by then and thus minimising the risk of unforeseen equipment swaps.

they will not have more A380 by then; so no improvement on the A380 routes unless they change either LHR or FRA on the second flight

What I meant was that there will be less unforeseen swaps due to having to cover elsewhere in the network, and thus 77Ws being sent to LHR instead of 380s. I.e. if the schedule is 380 now, and nothign unforeseen happens, it will stay that way - unless of course they change things around for the winter schedule for 2019/20 - which is something that can happen with any carrier, not just Thai. :)

as I understood they had for the winter schedule planned to have A380 on all daily flights for LHR (910/911), FRA (920/921), CDG (930/931), which are all leaving BKK just around midnight and returning day+1 in the morning. Later they realized that this was not possible in order to keep preventive maintenance schedule and swapped (in the schedule, not unforeseen at last minute) some of the 910 and 920 (and an occasional 930) back to 77w
Have not heard about longer downtime of some of the A380 with last minute swaps during last 2-3 months

correct me if I am wrong!

Paris is much "safer" than LON or FRA - because TG has two daily flights to both, LON and FRA,which permits them to swap, but only one daily flight to CDG.
But they usually do announce these equipment changes rather early and seldom "last minute" only - the reason is that they seem to be operating only five A380 instead of six aircraft (for unknown reasons....)

If you must fly A380 in F, then fly Emirates.
If you chose TG, then no guarrantees you will get the flight in an A380 F in January next year.
"Getting Tg'd" is part and parcel of flying on Thai.
(Unless, of course, you are on "protected routes" such as HND and SYD,
where the Thai VVVIPs would dare not fly in business, and TG would consequently dare not swap out for an aircraft without F - someone would get fired! )

Where does premium economy come from? OP is asking about F, and a possible swap to equipment without F (777 etc).
Reason why TG swaps is irrelevant. Just the insolence, lack of fore planning and frequency they do it that inconveniences passengers.
See this log (link) of the frequently occurring changes (just the ones that are actually planed and published, not all the "getting TG'd" swaps!)
The airlines you mention SQ/NH/JL/SK have larger and more stable fleets of wide body frames, and rarely swap last minute unless it is a same day mechanical, and even then, the swaps are typically of the same calibre metal.
From my personal experience with over 50 flights on TG (Asia/Europe/Australia), swaps are so common that I no longer get suprised.
What would irk anyone is for a swap that removes F, or downgages and some biz passengers get pushed out to Y, or even metal changes that convert lie flats in biz to the 747 recliners (like what they did to the HND route for winter 2018...F getting restored was nice, but a 777 lie flat to 747 recliner is horrendous).

OP should avoid TG if his/her goal is to guarrantee F. LH/LX/EK are better bets than TG.

Getting Tg'd is no longer news, IMHO.

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From Dec 27th
Thai Airways International this week filed planned Airbus A380 European operation for summer 2019 season. Planned changes as follow.

Bangkok – Frankfurt eff 31JUL19 TG920/921 A380 replaces 777-300ER, 1 daily (No A380 service from 29MAR19 to 30JUL19)
Bangkok – London Heathrow 01AUG19 – 30SEP19 TG910/911 777-300ER replaces A380
Bangkok – Paris CDG 01OCT19 – 26OCT19 777-300ER replaces A380
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From Feb 1st.

Thai Airways International this week gradually filed service changes for its international service, effective 31MAR19. As of 31JAN19, planned changes as follows.
Bangkok – Frankfurt
eff 31MAR19 TG922/923 A350-900XWB replaces 777-300ER, 4 weekly
eff 31JUL19 TG920/921 A380 replaces 777-300ER, 1 daily (No A380 service from 29MAR19 to 30JUL19)

Bangkok – London Heathrow 01AUG19 – 30SEP19 TG910/911 777-300ER replaces A380
Bangkok – Paris CDG 01OCT19 – 26OCT19 777-300ER replaces A380
Bangkok – Phuket – Frankfurt eff 31MAR19 A350-900XWB replaces 777-300ER, 3 weekly

Bangkok – Bangalore 01SEP19 – 30SEP19 777-300 replaces -200ER, 1 daily
Bangkok – Brisbane eff 31MAR19 777-200ER continues operating 4 weekly, replacing previously filed 787-8
Bangkok – Delhi eff 31MAR19 Increase from 19 to 21 weekly. Planned aircraft changes as follow:
TG315/316 747-400 replaces 777-300
TG323/324 787-8 replaces 777-200ER
TG331/332 777-200ER replaces 787-8

Bangkok – Denpasar eff 31MAR19 747-400 replaces previously filed 777-300
Bangkok – Guangzhou eff 31MAR19 Operational aircraft changes
TG668/669 747-400 replaces previously filed A350-900XWB
TG678/679 A350-900XWB replaces previously filed 777-200ER

Bangkok – Hanoi eff 31MAR19 A330-300 operates 2 daily, replacing previously filed 787-8
Bangkok – Ho Chi Minh City eff 31MAR19 TG556/557 777-200ER replaces A330-300 (Overall 1 daily each 777 and A330)
Bangkok – Hong Kong eff 31MAR19 Operational aircraft changes
TG628/629 A330-300 replaces previously filed 777-300
TG606/607 A350-900XWB replaces 777-300ER

Bangkok – Islamabad eff 31MAR19 Increase from 4 to 5 weekly, A330-300 operating
Bangkok – Jakarta eff 31MAR19 A330-300 operates 2 daily, replacing previously filed 1 daily each 777-200ER and 787-8
Bangkok – Kunming eff 31MAR19 777-200ER replaces A330-300, 1 daily
Bangkok – Manila eff 31MAR19 TG620/621 777-200ER continues operating, replacing previously filed 787-8 (Overall remains 2 daily 777)
Bangkok – Nagoya eff 31MAR19 A350-900XWB continues to operate 2 daily, replacing previously filed 1 daily each 777-300ER/787-8
Bangkok – Osaka Kansai eff 31MAR19 TG672/673 777-300ER continues operating, replacing previously filed A350-900XWB
Bangkok – Sapporo New Chitose eff 31MAR19 777-300 replaces previously filed -200ER
Bangkok – Seoul Incheon eff 31MAR19 Operational aircraft changes
TG654/655 777-200ER replaces -300
TG688/689 747-400 replaces A350-900XWB (4 weekly)
TG656/657 777-300 replaces -200ER

Bangkok – Shanghai Pu Dong eff 31MAR19 Operational aircraft changes
TG662/663 A350-900XWB replaces A330-300
TG664/665 777-300ER replaces A350-900XWB

Bangkok – Tokyo Haneda eff 31MAR19 747-400 continues operating 2 daily, replacing previously filed A350-900XWB
Bangkok – Tokyo Narita eff 31MAR19 TG642/643 A330-300 replaces previously filed A350-900XWB (Overall 2 daily A330 and 1 daily A380)

dear Tokyoite
no idea why you post here this long list...those are normal schedule changes (given the fleet with too many different aircraft types in comparison with the small fleet and the ongoing severe Problems with the 787 aircrafts…) and not the mentioned last minute aircraft swap

TG has improved a lot regarding last minute unforeseen aircraft swaps. For my last 50 flights I recall only one case (77w to 747) and this was announced around 3 weeks in advance and I got a F seat automatically for my J ticket...