Mr. Molnar, who died on Thursday at 33, was fascinated by the concept of modern flight. He traveled to obscure spots near New York's airports to get the best possible view of passing aircraft. He frequently discussed the ups and downs of the volatile aviation industry with friends. And he marveled at the slow, stately beauty of a 400-ton airliner gliding through the nighttime sky.

Eventually, Mr. Molnar turned his interest into an occupation. About four years ago, he stopped working at magazines and joined a Web site, nycaviation.com, that had been started by a friend, Phil Derner Jr. Mr. Molnar assumed the title of editor and director of technology, Mr. Derner said, and led a transformation of the Web site from an online newsletter for "local nerds who enjoy airplanes" to a respected publication that sometimes broke aviation news and was cited by mainstream news organizations.

Mr. Molnar died on Thursday evening of cardiac arrest brought on by a brain aneurysm, according to Mr. Derner, who said he received the news from Mr. Molnar's fiancée, Gina Masullo.

His death shocked many in the world of aviation.

"He was dedicated to being one of the first with a story," David Parker Brown, an aviation writer from Seattle, wrote in an e-mail. "I don't know anyone else who had the pulse of aviation in N.Y.C., like Matt did."

The Web site boardingarea.com posted a message saying, "Next time you see a plane fly overhead take a moment to watch it until it disappears from view, if for no other reason than a great aviation geek is no longer here to do it himself," and adding: "Happy Flying Matt, wherever you are."

In a telephone interview on Saturday Mr. Derner said that he and Mr. Molnar grew up in Queens, home to both La Guardia and Kennedy Airports, and enjoyed watching jetliners soaring overhead. They also shared an interest in trains and the two became friends around 2000 while volunteering with the Straphangers Campaign, an advocacy group promoting public transportation.

"We started to learn about plane spotting," Mr. Derner said, referring to the practice of seeking out areas near airports from which to closely observe jets taking off and landing. He added: "We forgot about trains pretty fast."

In 2003, Mr. Derner, an airline dispatcher, started a Web site that became nycaviation.com, which initially served as an informational hub for fellow plane spotters, who shared photographs of jets and tips on the best vantages from which to watch for them.

Mr. Molnar joined the Web site in 2009 and concentrated on providing more news and using social media. That year, Mr. Derner said, their Web site received attention from mainstream news organizations after Mr. Molnar reported that diamondback terrapins had wandered onto the tarmac at Kennedy Airport and caused delays.

Over the next few years the Web site became more professional, Mr. Derner said, sometimes breaking the news of fatal crashes and was cited by news organizations like CNN and NBC.

The Web site will continue to operate, Mr. Derner said, but will suffer from Mr. Molnar's absence. Mr. Molnar's many friends will also suffer, Mr. Derner said.

"Matt was always very soft-spoken, never got angry," he said. "His wit was completely unmatched."