: I took a short video of the Airline jumping through GMT hours - it
: definitely seems to "ignore" the 24-hour bezel as it
: moves along a 12-hour scale.

: https://youtu.be/NK1vnZ0cFl4

Hi, it's me again. I found your question interesting so I did some checking. I do have some old Heuer catalogs but have never seen this model. I found out that a watch like this just recently sold by a Swiss dealer so I got a good picture of it (appreciate you video). There was no description on the functionality of the watch in the add.
So here my evaluation. From the video and your description it appears that the extra hand (jumping one hour at a push) is strictly a second Hour hand to make a quick change of local time when you travel to a different time zone. (exp. From East Coast to California ). The watch then shows HOME time on the regular Hour hand and the "Jumper" Hand shows the hour in California.
The 24 Hour scale (inside on the face) and the 24 hour BEZEL I consider decoration with no functional purpose, ie. useless. Nothing to do with GMT. I do believe that once the customers found out this limitation, they did not purchase this model and it disappeared from the market.
Hope this helps. It is a nice looking watch but the functionality leaves something to be desired. Regards, Heinz.