Mr. Hobica told of wearing a navy blue suit on a United flight a few years ago from Kennedy International Airport in New York to Los Angeles, where he lives.
“I was in the lounge, where everybody was dressed in sandals and gym clothes, and I heard them call my name,” he said. He thought he was being bumped, but instead he was upgraded to first class.
“I don’t have status on any airline,” he said, “because I only buy based on price.” He concluded that the freshly pressed suit was the source of his luck.
Mr. Hobica then relayed tales of friends who had been upgraded while wearing clothes they considered nicer than what they might wear to the gym or the grocery store, and a conversation he once had with a gate agent friend at Lufthansa.
“She told me she would upgrade people based on how good-looking they are, how pregnant they are, or how nicely they’re dressed,” he said. “She said: ‘Look, we oversell flights and, of course, we go down the status list first. Absolutely, we look at your miles.’” But if no one on the flight warrants special privileges, the absence of ripped jeans or tattered sneakers can help, Mr. Hobica said.
Ashton Morrow, a Delta spokeswoman, said her airline, like most, adheres to set corporate practices that do not take appearances into account in selecting passengers for unexpected perks.
“There’s a number of factors that go into upgrading, including loyalty and recent delays we might want to make up for,” she said. “Upgrading based on wardrobe is never our policy.”
Still, dressing well for flights may yield more subtle benefits.
“I will say that when I see someone come on the plane and they’re dressed nicely and their children are dressed nicely, I do take notice,” said Kate Linder, an actress, and a United flight attendant since 1978.
That does not mean, she said, that she will pour full cans of ginger ale for the well-dressed passengers while their neighbors in flip-flops receive half cans, or that she is more inclined to be especially attentive to those well-dressed passengers. But she said she remembered a time when most customers considered flying an occasion to dress up, and she suspects one result was increased civility for everyone on board, particularly those who paid closest attention to their appearance.
“When someone is a little dressed up and looking like they made an effort, it’s almost like they’re showing respect for themselves and for everybody else on the plane,” said Ms. Linder, of Los Angeles, who has maintained her career as a flight attendant while also appearing on the TV soap opera “The Young and the Restless.”
“My personal opinion is that when you take pride in how you look, you take pride in how you act,” she said.
Nancy Marquis, another longtime United flight attendant, retired in 2007 but is still a frequent flier. She said she understood the inclination to dress “like a slob” on a plane.
When she became a flight attendant in 1969, seats were bigger and security was not as much of a bother. Now, she said, “you have less personal space and fewer amenities, so you want to be as comfortable as possible.”
Ms. Marquis, of Glen, N.H., said she thought the evolution of less formal dress for flights could be traced to 1978, the year the Airline Deregulation Act became law. “That was a definite demarcation line. New airlines started popping up and fare wars started,” she said.
For many, the democratization of air travel meant that buying a plane ticket no longer merited a trip to the dry cleaner. But one thing stayed the same, Ms. Marquis said: Regardless of where passengers were seated on a plane, in economy or in a premium section, everyone dressed similarly.
Before deregulation, everyone was dressed for a business meeting and no one wore jeans, she said. Now, no one is dressed for a meeting and everyone wears jeans.
There is a relatively new twist to that trend of dressing similarly. Airlines including American, United and Delta have started offering first- and business-class international passengers free pajamas on overnight flights in recent years, according to Mr. Sumers — something he said was more closely associated with Asian and European airlines.
One result could be an antidote to the withering looks from passengers who do not approve of seatmates’ hoodies and sweatpants, and an overall avoidance of skirmishes over what is appropriate airplane attire.
“The pajamas are a wonderful trend,” Mr. Sumers said. “It can be truly bizarre, because you’ll have like 60 seats in business class, and 40 of the passengers have decided to wear the pajamas. So for like 10 hours, everybody is matching.”
Ms. Marquis said everybody was probably more at ease, too.
“If you look fabulous or you look horrendous on an airplane, you’re going to stick out,” she said. “If you’re dressed like everybody else, there are no extremes and you have nothing to worry about.”