This is a short warning about cats and dogs in cargo holds. If you are traveling with your cat or dog and your companion animal is in the cargo hold of the aircraft, my advice is, just after you have taken your seat in the cabin, to ask the stewardess to check with the captain that the heating has been turned on in the hold (the space below you where luggage etc is stored).
There was a case, which appears to be unreported, in which a dog froze to death on a flight from Paris to Canada. I don’t know the exact destination and I don’t want to mention the airlines, but what a terrible death and it must have been extremely traumatic for the dog’s human caretaker.
The temperature in the cargo is not sub-freezing but it can be cold enough over a long flight to hurt an animal, it seems to me. The temperature in the cargo hold probably depends on the flight path.
The captain failed to flick a switch that would have turned on the heat in the hold of the aircraft. I don’t know if the heating can be controlled such that it heats sections of the hold. I would have thought it could be controlled like that (update: the aft [rear] cargo compartment is pressurized/ temperature controlled). Apparently the captain turns on the ACM, (air cycle machine) that ensures the same temperatures in the cabin and the temperature controlled cargo hold.
I also presume that the captain is notified in paperwork that there are animals or an animal in the hold. If he isn’t or if he forgets that a cat or dog is in the hold, it will become extremely cold unless it is heated. On a long flight it will be cold enough to kill a companion animal.
I have it on first hand experience that a seasoned air traveller asked the airline employees in the departure lounge if his dog was OK in the hold and whether it was heated. He was reassured. Again he asked the flight attendant when he sat down in his seat on the aircraft as it was being loaded with passengers. The flight attendant stated she would check with the captain which she did. The captain flicked the switch to heat the hold.
This dog owner was concerned. He was vigilant and he made sure his dog was OK. I think this demonstrates a beautifully intense concern for his animal companion.
I believe it is sensible to do this. If ever I travel by air with my cat, I’ll ask. I believe we should. We are in charge of the safety of our cat when flying. There is no one else to blame if something goes fatally wrong.

I don’t remember any of my cats suffering any long-term bad effects from travelling by plane. what upsets them the most is being in the car on the way to the airport. Of course I have no idea how they react to being in the cargo hold. I imagine take-off and landing would be terrifying. But inevitably when I pick them up in the baggage hall they seem relaxed and even happy.
It must be nerve wracking for both the caretaker and the cats and to be avoided if at all possible.
Cats must be totally out of their comfort zone being trapped in and airborne and I wonder too how many don’t survive and also how many are traumatised for life.
I know people who are terrified of flying and I think cats probably would be too if they knew what was going to happen when they were first put in their cat carrier for the journey.
Cats are not allowed in the cabin on flights over 5 hours. I suppose it varies from airline to airline but generally speaking they have to go in the hold on long flights. They have to be in their carriers for a lot longer than that. From leaving my house to take-off takes another 2-2.5 hours. And what if you suddenly get lumbered at the last minute with an Airbus with no in-hold accommodation and the flight is longer than the permitted time? All your plans come crashing down. Even when everything goes to plan it is still a nerve-wracking experience.