Prometheus Rebound by Daniel F. Galouye. The story is from 1970 and I read it in the anthology The Year 2000, which according to ISFDB is the only place it's been published in English.
The ship is the Prometheus Unbound:
Like Triumphant Prometheus, unfettered at last from his storm-thrashed rock, the huge fluxliner heaved up through the final shrouds of resistive atmosphere, majestically treading the fabric of geomagnetic space.
Almost the width of a city block and massing some 350 tons, Transequatorial Fluxways’ flagship was a scintillating disk whose 2231-aluminum hull arrogantly flung back the rays of a midmorning sun. Her sheening surface was broken only by circumferential ports—scores of eyes staring out into the depth of space and back at the receding North American coast line.
Ahead—little more than an hour from New York via magnetic field navigation—lay Flight 201’s destination: Buenos Aires
As you say, the incident was created by one of the stewardesses, who is actually a "Civil Magnetonautics Bureau Inspector":
Elaine’s sobs drowned out his words and she exposed a tear-streaked face. “It’s not him,” she said remorsefully. “It’s me”.
“What’s you?” Martin asked, confounded.
Her seat dipped almost to the horizontal, rotated, then swung back toward vertical. “I’m the CBM inspector,” she sobbed. “I shorted out the erect Rutledge coil lead with a bobby pin—to see how you’d react.”
The old man is Ira Ambrose, who was a famous pilot in his day. The quisling reference that jogged my memory comes when one of the pilots accused Ira of being an undercover inspector:
“Are you or aren’t you a Magnetonautics Bureau inspector?”
“Eh?” Ira repeated. Then his puzzled frown was buried under an expression of senile amusement. “See what you’re getting at. You think—” He paused, croaking out a laugh. “No, I’m no quisling. Flew for the airlines after the war. And there was this goldbricking CAB inspector who came pussyfootin’ around and—”