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Guest CRJ700FO

cabin temp at cruise altitudes

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I looked at the plane status in the I-map feature while cruising in the vir a346, it read:ALT: FL400Outside air TEMP:-40degthe ACs were still running, delivering cold air, there was a little freeze on the outer glass of the window; yet it was pretty comfortable inside.How is that possible at such low ambient air temp without any heaters running?

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I doubt that the AC was delivering air at -40 degC to the cabin - in which case it must have been heated.

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>I looked at the plane status in the I-map feature while>cruising in the vir a346, it read:>ALT: FL400>Outside air TEMP:-40deg>>the ACs were still running, delivering cold air, there was a>little freeze on the outer glass of the window; yet it was>pretty comfortable inside.>How is that possible at such low ambient air temp without any>heaters running?There are heaters running. Four of them. Two hung underneath each wing. They are called engines. Hot compressed air is tapped from the engines for the pressurisation and air conditioning systems. This air is usually several hundred degrees hot as it comes out of the engines before it is run through devices usually called PACs that bring it to breatheable temperatures before pumping it into the cabin to pressurise and air condition it.

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Yeah that ^The temperatures are so hot that you'll have the worlds best sauna even at FL410

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Pack's are air cycle machines. This should give you the lowdown on how they work: http://en.wikipedia.org/wiki/Air_cycle_machineOn a related engine generated heat topic.....Aircraft also use the hot engine oil to heat the fuel to keep it from freezing. This process cools the oil and returns some hot fuel back to the wing to keep the fuel from freezing.

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