For what its worth, nothing about commercial airplanes is a "closed-air-circulation system". The air is continually refreshed from the outside at a rate of about 20 times per hour.

http://www.nbcnews.com/id/34708785/ns/travel-travel_tips/t/a...

Airplanes aren’t closed-air circulation systems. Air is pulled in from the outside and heated before being injected into the cabin which releases air to the atmosphere directly through openings on the aircraft. You get more fresh are on airplane than you do in the airport you were sitting in before you boarded it.

IIRC it's 50% recycled to save money

How would that save money?

Probably the cost of heating -50°F air to cabin temperature.

Heating isn't a problem, cooling is. Most aircraft use "bleed air" from the compressor on the engine. That air is extremely hot (>150°C), so it requires a lot of cooling. Aircraft air conditioners are known as "packs" or "air-cycle machines", as they don't use any refrigerant, just compression/expansion and heat exchange with the outside air. This is also why you can smell oil and jet fuel when the engines start.

Air isn't recycled in to this system because the cabin pressure is too low, but air already inside the cabin is circulated around to avoid it stagnating.

Wouldn't that be heated with waste engine heat?

It's heated using waste heat from the engines (jet engines generate a lot of heat...)

I’m sure you could have asked to have been moved. Ironically they won’t serve peanuts if anyone is deadly allergic.

Ironically? Peanut allergies tend to be leagues worse than pet allergies, not that the latter should be discounted completely.

It's exceedingly rare for airlines to even have peanuts as an option for this reason (maybe never?). Do you remember any recent examples where they had them?

Fairly recently with southwest. Delta seems to have switched to almonds instead - which IMO are better.

You're lucky if you get any snacks though these days.

I fly relatively frequently across a wide array of airlines and even before this discussion noticed the stark absence of peanuts. I can even picture the red Southwest branded packet of pretzels as the “default classic” option. Hmm, interesting.

Edit: Can confirm, no more peanuts on Southwest either: https://www.cnbc.com/2018/07/09/southwest-airlines-is-gettin...

Weird, definitely got a pack of peanuts a couple months ago from SW. Wonder if they were just using up their stockpile then...

> You're lucky if you get any snacks though these days.

Or the snacks are pointless. On a recent delta flight they handed out baby carrots from a bag.

I get nuts all the time on Alaska and I think American, but perhaps no peanuts.