Four Russian warplanes on Tuesday flew just outside of United States airspace near Alaska, the North American Aerospace Defense Command said, marking the latest incident involving Russian aircraft off the coast of the U.S. state.

The military operation was routine, according to the agency, which detected and tracked the planes. Although the Russian aircraft remained in international air space, they entered a region beyond U.S. and Canadian sovereign air space called the Air Defense Identification Zone (ADIZ), where aircraft are expected to identify themselves, according to NORAD.

The ADIZ is a stretch of international air space bordering the sovereign space around the U.S. and Canada, which both countries monitor in order to, ideally, readily detect all aircraft passing through. Surveillance in the defense zone is maintained for national security reasons.

NORAD said it uses a “network of satellites, ground-based and airborne radars and fighter aircraft to detect and track aircraft and inform appropriate actions” and “remains ready to employ a number of response options in defense of North America.”

The U.S. military reported similar actions from four Russian warplanes detected off the coast of Alaska in February and September. The report in September happened shortly after more than 100 U.S. soldiers were deployed temporarily to Alaska’s remote Shemya Island in response to a spike in Russian military activity off the western boundaries of North America, which a U.S. general described as an exercise to test the military’s readiness to deploy troops and equipment.

Their deployment coincided with eight Russian aircraft and four navy vessels, including two submarines, traveling close to Alaska while Russia and China conducted joint military drills. None of those planes entered U.S. air space.

On Sept. 30, NORAD posted a dramatic video of a Russian fighter jet flying close to a NORAD aircraft off the coast of Alaska. At the time, a U.S. geneal said “the conduct of one Russian Su-35 was unsafe, unprofessional, and endangered all.”

Russian warplanes have also been detected in neighboring air spaces in recent months. In November, NATO said Italy and Norway had each scrambled jets after Russian aircraft were seen over the Baltic Sea and along the Norwegian coast. NATO did not share details about the Russian activity but said the planes were “not adhering to international norms” when Italian and Norwegian forces were mobilized. Russia has ramped up military operations in the Arctic Circle, which includes part of Norway. 

South Korea’s military also said it scrambled fighter jets in November after five Chinese and six Russian military planes entered its air defense zone but did not cross into the country’s air space.

The Associated Press and AFP contributed reporting.

Iconic rock band the Grateful Dead was named a Kennedy Center honoree earlier this year, celebrating decades of their innovation and success.

“It’s a legacy thing for me and us, I think,” drummer Mickey Hart said of the honor.

The surviving members — Bobby Weir, Bill Kreutzmann and Hart — told “CBS Mornings” the honor is not just for the band members, but for their fans.

“They kept us goin,'” Weir said.

Grateful Dead forms

The band formed in the San Francisco Bay area in the mid 1960s. Weir was 16 when he first heard Jerry Garcia playing banjo outside a music shop in Palo Alto.

“It was New Year’s Eve, basically he invited us in. We had enough fun that evening that we decided it was too much fun to walk away from,” Weir said.

Kreutzmann recalled seeing Garcia and Weir play at a club.

“I was totally blown away by Jerry’s ability to hold the audience in his hands. Jerry held the light for everybody,” he said. “That week he called me and said, ‘Hey, you wanna be in a band?’ I said, ‘Sure.'”

Kreutzmann later brought Hart into the band in 1967.

“Bill invited me to play and sit in. When I heard the band, I go, ‘Whoa.’ We all got turned on to the Grateful Dead in different ways, but we really got turned on to it,” Hart said. “We got bit.”

Garcia also recruited Phil Lesh, a classically trained musician, to play bass. Lesh, one of the band’s original members, died in October at 84 years old.

Grateful Dead’s legacy

In their 30 years as a band, the Grateful Dead scored just one Top 40 hit with “Touch of Grey,” and not a single Grammy nomination.

“We’ve had people come up to us, say, ‘You guys are never gonna make it. You play too long. You play too loud,'” Kreutzmann recalled.

But through their decades together, they built a legion of followers known as “Deadheads,” who started recording and sharing their concerts.

“You’d look from the stage and it looked like a forest of trees of microphones,” Kreutzmann said of their fans recording their concerts.

Their record company advised against allowing fans to record, but the band refused, saying they weren’t worried about piracy.

“It was the smartest thing we ever did,” Kreutzmann said.

The Grateful Dead played more than 2,300 concerts and fans recorded most of them.

“Those cassettes went out all over the world,” Hart said. “They were our archivists as well.”

When Garcia died in 1995, the band broke up after 30 years together. They weren’t sure they could find a way to carry on without their frontman. 

“When Jerry left that was the end of the Grateful Dead. Period. There’s just no way that you can replace a Jerry Garcia,” Kreutzmann said.

The surviving members went off to start other projects and bands, but the Grateful Dead’s spirit would always live on. Weir said Garcia visits him in dreams from time to time, including recently.

“In the dream, Jerry comes to me and he says, ‘Listen, I’m gonna invite a song in to meet you. I want you to meet this song.’ … What that dream did was, it solidified in me the notion that, yes when we play the songs, they’re living things,” Weir said. “They come and visit our world and they come through us.”

Anthony Mason

Anthony Mason is a senior culture and senior national correspondent for CBS News. He has been a frequent contributor to “CBS Sunday Morning.”