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Catch Me If You Can: How Alaska Airlines Flight 870 Intercepted A Total Solar Eclipse Over The Pacific

Here’s a tricky word problem: A scheduled commercial jet carrying a bellyful of astronomy geeks takes off hours before a total solar eclipse from Alaska’s Anchorage International Airport heading to Honolulu. Along the 2,800-mile trip, the Boeing 737 intercepts the eclipse’s narrow shadow speeding across the Pacific Ocean, hides inside it for a few minutes and continues on its journey. How did they do it? One word: software.

“Here’s a football analogy,” says veteran pilot, instructor and engineer Hal Andersen, who was in charge of the Alaska Airlines flight last March. “Think of the airplane as a football, the software as the quarterback and the eclipse shadow as the receiver. The quarterback in this case launched the football out of Anchorage and got it into the arms of the receiver running across the field at 10,000 miles per hour thousands of miles away.”


Top image: On March 8, 2016, Alaska Airlines flight 870 observed a total solar eclipse in the middle of the Pacific Ocean. Above: Flight 870 was traveling from Anchorage to Honolulu. Images credit: Alaska Airlines

Developed by GE Aviation, the software, called flight management system (FMS), works inside thousands of aircraft flying around the world. It lets pilots precisely plan their journey and fly in the most optimal manner. It can accurately position the plane to any point in the flight plan with a time of arrival within 10 seconds. This precision comes in handy when you want to catch a fast-moving shadow in the middle of the world’s largest ocean.

The plan to intercept the eclipse that took place over the Pacific on March 8 was hatched by astronomy enthusiasts a year ago. Members of the American Astronomical Society with serious math skills broke down exactly when and where the shadow would fall as the moon swung between Earth and the sun. After they figured out the eclipse’s precise trajectory, they went looking for commercial flights that sliced through it at about the right time. The idea was to buy window seats and watch the show from 30,000 feet, where a boat wasn’t needed and clouds wouldn’t obstruct the view.

Limiting their search to flights that reliably departed and arrived on time, the group landed on Alaska Airlines’ flight 870. But the plan had a flaw. The scheduled departure time put the aircraft at the right location 25 minutes too early.

Rather than taking a gamble on a fortuitous delay, the group reached out to the airline. To their surprise, the carrier agreed to alter the flight and make the celestial rendezvous happen.


Hal Andersen was piloting an Alaska Airlines Boeing 737-800, a plane like the one pictured,  when he intercepted a total solar eclipse on March 8. Image credit: Alaska Airlines

It was cloudy when flight 870 took off from Anchorage just after 2:15 p.m. local time. With 181 passengers on board, the Boeing slashed through the cloud deck at 5,000 feet to bask in the sun for the six-hour trip to Honolulu.

The air inside the cabin was charged with anticipation and nervous energy. Even with the new computed flight plan, Andersen had only about 30 seconds of wiggle room to arrive on time.

In order to allow the passengers to see the eclipse from their windows, Andersen needed to cross its path perpendicularly and manage powerful 160-mph crosswinds that were pushing the plane away.

But the software made adjustments on the fly to keep everything under control and on schedule. Andersen programmed the FMS to track location, weather data and other parameters and used its navigation commands to pilot the plane to the meeting point.Solar-Eclipse_1

Just after 5:30 p.m., around 700 miles north of Honolulu and 35,000 feet over the Pacific, it was show time for passengers on the right side of the plane. The moon started sliding in front of the sun like a manhole cover and a shadow 68 miles wide began sprinting from Southeast Asia eastward toward them. Astonished whispers quickly replaced cheering on board as the shadow engulfed the cloud deck below them and then the plane itself. “For people who have seen a total solar eclipse, these are the most spectacular events they will see in their life,” Bob Stephens, an accountant and amateur astronomer, told Alaska Airlines. “That’s why people start chasing them – you have to see another.”

Andersen watched the eclipse from the cockpit. “We had the best view of any human on Earth during those two minutes, and it was amazing,” he said.

He also saved some praise for the navigation software. “I was very proud of the system,” he said. “It did a great job demonstrating its power and capability. I’d give it a pat on the back.”

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