The story behind the Delta flight that raced Hurricane Irma

For the crew of Delta flight 431, the ride through the outer bands of Hurricane Irma last Wednesday was "uneventful."

It was breathtaking for those who watched the aircraft on radar flying down to Puerto Rico and back to New York just before the Category 5 storm crashed the Caribbean. It was a tactical operation that put the Boeing 737-900ER on a mission to rescue 173 passengers in San Juan, eager to escape the storm.

"We felt confident we could get a flight in and get those customers out, and do it safely," said Janine Mardell, the flight superintendent at Delta's operations center in Atlanta, who coordinated the flight plan. "It's what we do."

But it wasn't an ordinary day nor flight. It was the last passenger jet to leave San Juan before Irma hit and the crew's bold effort getting in and out of Luis Muñoz Marín International Airport – captured on radar – made it an Internet sensation. Its crew became heroes in the Twitterverse after successfully journeying through the storm with such calm. Three other flights, out of South Florida, had tried to get to San Juan that morning, and all turned back, unsuccessful.

"It was a little surprising to see this Delta flight continuing on," aviation blogger Jason Rabinowitz said in an interview. He tracked the flight throughout the entire trip, cheering it on. "An absolutely amazing job . . .," he tweeted as the full flight took off for New York's JFK airport.

The quick-turn mission was carefully orchestrated, Delta said in a detailed account of the flight, that provides insight from Mardell and crew members.

In Atlanta, Mardell and Delta's meteorology team cooked up a plan, carefully looking at Irma's threat. In San Juan, a team of airline employees prepped the 173 passengers for early departure, and got government officials, TSA and the airport authority on board with the plan.

"With Irma's outer band already hitting Puerto Rico, prompting other flights to divert, Delta meteorologists were confident the band would pass, creating a window during which winds and rain would subside significantly and allow for the flight's safe arrival," Delta said.

[Hurricane Irma reduced a once-lush gem in the U.S. Virgin Islands to a wasteland]

Before leaving New York, pilot Capt. Ben Vorhees and his crew huddled to go over the plan and forecast with Mardell. If conditions changed, there was a backup plan to land in Miami.

"It wasn't even that bumpy till we got close," Vorhees said. "We knew timing would be critical, but otherwise Janine and meteorology made it easy."

Flight 431 arrived at the gate a minute after noon to nine miles of visibility and light rain, the airline said. It had encountered light to moderate turbulence as it approached landing. Winds were well below safe operating limits at around 28 mph, and gusts up to 36 mph.

Irma was 90 miles away, which meant the window to get back in the air was short and boarding had to be smooth and quick. Boarding began just a few minutes later and at 12:41 p.m. the aircraft took off as DL302, with 173 passengers on board, flying in between Irma's bands.

Eight minutes later, the airport closed.

"It was just about planning and perfect timing to be able to get in and back out while the others had to turn around," Rabinowitz said. "Delta took this calculated risk. Had they gotten there and the weather had been poor, they would have had to return like everyone else."

And that would have been bad news for those passengers. Heavy rain and historic winds lashed Puerto Rico's northeast coast that afternoon as Irma roared through the Caribbean with gusts of up to 111 miles per hour.

There are few instances when passenger jets fly into areas under hurricane warnings. Airlines generally avoid such areas because the risks are too high, experts say. Had the Delta aircraft had a technical fault on the ground or a delay in refueling, chances are it would not have been able to take off.

"We knew that timing was crucial, and we worked in full coordination above and below wing as well as with our vendors to get the flight refueled, serviced, boarded and dispatched in 40 minutes," said Michael Luciano, Delta's station manager in San Juan.

But the crew said they were prepared for rough weather.

"We were prepared for heavy windshear, crosswinds, strong tailwinds, but it was no worse than a summer thunderstorm in Atlanta," said Joyce, the pilot, who is based in New York.

The best part, Vikki Panan, one of the flight attendants, said in the Delta account, was getting the passengers out to safety.

"I am so proud of what we did," she said. "Those customers who flew out [of San Juan] were so grateful that we got them out. They clapped and cheered when we landed back safely in JFK."