It's the white gloves that do it. The white gloves and the tight hobble skirts. The tight hobble skirts and the cute pillbox hats. The cute pillbox hats and the undulating runway strut....
Actually, I'm not sure which part of the Pan Am air stewardess's uniform in 1963 could accurately be described as sexy, but something about the bright blue, two-piece outfits breathed a sophistication that had never been seen in a woman's uniform before.
In Pan Am, the new prime-time American TV drama series, four azure-clad stewardesses stride confidently through an airport lounge en route to their plane. Their hips sway in motion, their blue handbags are clamped to their perfect hips, their white-gloved hands are angled just so. A little girl watches through a window with an awestruck gaze that guarantees a lifetime of body dysmorphia, while one of the stewardesses looks back at her with a kindly gesture.
The scene is, of course, a pinch from Virgin Atlantic's 2009 TV ad that celebrated its quarter-century in the air.
It showed a dozen attractive young women in red two-piece uniforms, accessorised by red scarves and red high heels, striding through Heathrow to the pounding beat of Relax by Frankie Goes To Hollywood.
Look back a few years and you'll find the locus classicus of this air-hostess-harem stuff in a film called Catch Me If You Can, when con-man Frank Abagnale Jnr (played by Leonardo DiCaprio) signs up eight female students to don blue Pan Am uniforms and walk into an airport lounge with him, lending corroborative detail to his fake uniform and pilot's cap.
The 21st century has re-discovered something thought axiomatic in the 1960s: air hostesses are glamorous babes, half a step behind fashion supermodels, super-competent young women, single and available to a guy with the right combination of airmiles and Asprey bijoux.
That's the presumption behind the new TV series, of which the pilot (a confusing word in the circumstances) aired in the US on Sunday. In it, we get to know four girls who long to see the world and escape from the everyday pressure (in 1963) to find a husband, settle down and have babies.
There's Laura (Margot Robbie), Kate (Kelli Garner), Maggie (Christina Ricci) and Colette (Karine Vanasse).
It's a fantastically silly series, glossy and superficial and not a patch on Mad Men, but it rams home the message that, in the early 1960s, women were empowered by being allowed to serve martinis and reassure nervous passengers in huge planes.
While Mad Men charted a gradual evolution of gender equality, Pan Am starts with the proposition that the job of air hostess represented freedom -- even as it showed girls being forced to wear girdles, being weighed before flights and risking being fired for getting pregnant.
Was it really like that? "Life with Pan Am was very glossy in the late Fifties," says Diane Markwell, now 74, who, as 21-year-old Diane Little, was one of the first British girls to squeeze into the blue uniform.
"We were the best-dressed, highest paid people in the airline industry. TWA stewardesses were looked down on as a bit raffish, Boac were a bunch of dykes and then there was us. We were called 'hostesses' by the way, not 'stewardesses'."
Had Markwell ever been harassed by lecherous/ drunk/impertinent passengers? "Oh no," she says. "But you must remember, in the 1950s, people who flew were generally well-educated and well-off and they wouldn't misbehave. It wasn't like today. People dressed up to fly: gentlemen in suits and ladies in full fig."
Had she been the object of entirely proper overtures, then? "There was one man," she says, "a Canadian millionaire, the president of a gas company. We'd been chatting away for a while at Heathrow -- and nothing untoward happened whatsoever -- but after he'd left on his plane, I discovered he'd put £100 in my handbag. It was a huge amount in 1958 -- it paid my rent for a month."
The Canadian magnate who was so grateful for her girlish reassurance was, she recalled, a shareholder in the Skyways Hotel at Heathrow. "I got a few hot dinners out of that place," she says. How? "The management used to ring up and invite some of us, in our uniforms, to come over and just... stand around. Oh, and to use the swimming pool of course, if we brought a bathing costume."
How piquant to think of a innocent time when air hostesses, in their azure two-pieces, tight skirts and pillbox hats, could be called in like human decor, to hang out, be gazed at and admired -- not as rideable sexpots, but as the epitome of female grace.
Pan Am will be screened on BBC2 from November.