The day started with so much promise.

After weeks of waiting for the clouds to part, adventure aviator Gus McLeod had clear skies over the Montgomery County Airpark yesterday, a crowd of admirers and television cameras and a 17-foot airplane he believed was ready to redeem his failed attempt last year to become the first person to circumnavigate the globe over both poles in a single-engine aircraft.

The day ended with a despondent pilot and a broken airplane slumped in a hangar 30 miles away in Frederick.

"We've got a disaster," McLeod said from the hangar. "I feel embarrassed. I don't know what to say. . . . I don't have a clue as to what failed or why it failed -- all I know is it failed."

Not long after McLeod signed an autograph for a young boy, hopped into the cockpit of the Firefly, waved goodbye to the crowd and launched into the sky headed for the North Pole, he felt something was wrong.

"I couldn't put my finger on it. The vibration was off; it was doing something amiss," said McLeod, 50, of Gaithersburg. So he decided to land at Frederick Municipal Airport. When the front wheel touched down, he heard a pop. He pulled up, and then set the wheel down again. More popping, he said, until finally, it smoothed out and rolled normally. When he got out of the plane, he found the protective covering for the wheel had been partially torn off.

Rather than wait to repair it, McLeod tore it off completely.

"That's going to take too long to fix, and it's not a necessity," he said.

But when he taxied back onto the runway to resume his flight, the front landing gear collapsed and the nose of the plane lurched down onto the runway. McLeod, who plans to take the Firefly to Baltimore for repairs, spent the afternoon disassembling parts of the airplane and worrying about the consequences.

"It may mean that I go in the spring. It may mean I go to the South Pole first," he said. "But I'm still in it, I'm still in the race, I'm not giving up by any stretch of the imagination. It's not in me to give up."

McLeod is nothing if not resilient. His wife, Mary, has long since stopped believing him when he says the latest daredevil mission will be his last.

"He can't fool me," she said. "If he can get up in the airplane and do something else, he'll do it."

McLeod began flying at 14 and courted his future wife with dates at College Park Airport. In 2000, he became the first person to fly to the North Pole in an open-cockpit biplane, along the way suffering from hallucinations, frostbitten fingers and dysentery. Last year, he and his daughter Hera competed on the CBS reality show "The Amazing Race."

McLeod's latest adventure -- a three-month, 27-stop, round-the-globe flight -- was in pursuit of a familiar goal. Last year, he set out in the Firefly on the same mission, but the plane could not shake off the sheet of ice that coated its wings over Antarctica, and McLeod never came within 900 miles of the pole.

This time, the Korean-made Firefly, which McLeod calls his "flying Ferrari," was retooled to be lighter and more powerful. McLeod added a custom turbocharger, which he said boosted his top speed to about 260 miles an hour, up from 200, and he took out 100 gallons of fuel to lighten the load. He hoped that this would allow him to scoot over clouds of ice by maintaining full power up to an altitude of 28,000 feet. He had planned to leave earlier in the season to make it past Antarctica by December, when the weather is, he hopes, less wild.

Unlike his open-cockpit flight to the North Pole, a trip in which he experienced discomfort to the point of "being on the verge of death and not caring," the challenges in this trip are less a test of his endurance than the Firefly's. In his previous round-the-world attempt, mechanical problems delayed the early legs, and water in the gas tanks forced him to make an emergency landing on a pothole-ridden dirt path in Argentina.

"If the engine makes it, I make it," he said. "This is a technical challenge, a challenge of the skill of the pilot."

McLeod, a businessman and former CIA chemist, said he is motivated by the desire to instill excitement about science and aviation in young people, to provide an example of "someone who has accomplished something that isn't a sports star or a television star but had a pretty fruitful life."

He said the flights are harder on his family than they are on him, although he spent a sleepless night Saturday worrying about his preparations.

"All the stuff with my wife, all the goodbyes, all the 'Why are you doing it?' I had all that done," he said. "Now I've got all the hard part to do over again."

Barbara Ganson waves goodbye at Montgomery County Airpark as Gus McLeod, in the Firefly, begins his planned solo flight over the North and South poles.McLeod embraces his wife, Mary, before takeoff. She says she has stopped believing his promises to abandon daredevil flights.