I read somewhere that you need a fit-to-fly certificate and a covid test to be allowed to board a plane out of Thailand, but my airline has a "before you go" list which mentions neither of these. Where can I find something official?

Hey 

Maybe related to the country where you are going to 

Swiss bound flights and France bound do not require it.

It might be another matter for UK though.

It certainly depends where you’re intending flying to, some countries require a certificate and some don’t, the UK doesn’t, though you’d need to self isolate on arrival.

Some airlines require a fitness certification and some don’t.

This is what Emirates needs to go to or transit through Dubai  https://www.emirates.com/au/english/help/flying-to-and-from-dubai/tourists-travelling-to-dubai/

KLM to Schiphol don't need it,  Qatar do (via Abu Dhabi?)

Got on a eva air flight to uk in June and didn’t need anything. Suggest you look up government website of where you are going to see what their rules are about you arriving .

None by Thai authorities as long as you are not on overstay.

I flew out with my Thai wife to Paris a week ago. The airlines may have requirements depending on your destination, including transits. Etihad and Emirates both require Covid test result.

Getting back in to Thailand depends on whether you fit one of the allowed categories and must be done through the Thai Embassy in the country you want to return from, is by repatriation flight only at least from France and quarantining at your expense ( free for Thais) on arrival in Thailand.

19 hours ago, theoldgit said:

It certainly depends where you’re intending flying to, some countries require a certificate and some don’t, the UK doesn’t, though you’d need to self isolate on arrival.

Some airlines require a fitness certification and some don’t.

I think you mean a "Fit to fly" certificate. 

1 hour ago, Kalasin Jo said:

None by Thai authorities as long as you are not on overstay.

I flew out with my Thai wife to Paris a week ago. The airlines may have requirements depending on your destination, including transits. Etihad and Emirates both require Covid test result.

Getting back in to Thailand depends on whether you fit one of the allowed categories and must be done through the Thai Embassy in the country you want to return from, is by repatriation flight only at least from France and quarantining at your expense ( free for Thais) on arrival in Thailand.

It's only free for Thai nationals if they chose to be quarantined at a government facility.