Back in September 2010, I reported that the height of Southwest’s under-seat spaces, at least on a 737 -700 series plane, was 11 inches. In December 2010, however, reader David alerted me that on his flight, the under-seat space was reduced to 8.5 inches by a life-vest container. I was surprised and concerned, but, happily, I had five Southwest flights scheduled for December and could check the situation out for myself. Here’s what I learned.

We flew on three 737 -700 series planes, and two 737 -300 series planes. The measurements I made on all of our flights turned out to be the same, so there were no differences in this regard between Southwest’s -300 and -700 series planes. The under-seat width measurements were the same as those I reported in my December 2009 post. Now for the height measurement: On every flight, there was a hard plastic container for a life vest that reduced the under-seat space height to 9-9.5 inches. However, that container is positioned pretty far forward — about 7 inches from the part of the seat closest to your knees. The container itself is about 7 inches wide, so it leaves some full-height space on either side of it.

Chloe's carrier, oriented left-to-right on our SEA to STL flight

Because we typically use a large SturdiBag for Chloe, oriented left-to-right, the hard plastic life vest container was no problem for us. Our SturdiBag (and I swear I am not affiliated in any way with the SturdiProducts company!) is rounded on top, besides being very flexible, so it never ran into the life vest container.

I am also not surprised to hear from reader Lizabeth that her pup Avery traveled comfortably under a Southwest seat in her Sleepypod Air carrier. The picture Lizabeth posted on Dog Jaunt’s Facebook page shows Avery’s carrier oriented front-to-back under the seat — which would work, even though the Sleepypod Air is 10.5 inches tall, because the life vest compartment is not perfectly centered (at least under the middle seat), and the top of the Air will deflect a bit to one side.

I can well imagine that a large, rigid rectangular carrier (and when I say “rigid,” I mean not only hard-sided carriers, which you don’t see much these days, but also soft-sided carriers with firm edges) more than 9 inches tall would have some troubles with Southwest’s under-seat spaces.

I’m left, of course, wondering whether the one plane I measured last September was the only one in the fleet not equipped with hard life vest containers (because yes, I did reach all the way under to feel for obstructions)! This is yet another example of the awesomeness of Dog Jaunt’s readers. My thanks to reader David, and to all of you, for helping to make Dog Jaunt a better, more useful blog.