What causes turbulence, and how can it pose a danger to air travel? An expert explains

One person died and at least 85 people were admitted to hospitals after a Singapore Airlines flight from London to Singapore experienced severe turbulence Tuesday.

Deaths from turbulence are extremely rare. According to the Federal Aviation Administration, 163 passengers and crew on U.S. flights have been seriously injured by turbulence between 2009 and 2022, out of what the FAA says is more than 2.9 million people who fly in the U.S. every day.

Most anyone who has ever flown in an aircraft has experienced turbulence, when the ride becomes bumpy due to turbulent air – a common occurrence in air travel. Yet what exactly causes turbulence, especially the kind as severe as what Singapore Airlines flight SQ 321 experienced? And why was there apparently little to no warning?

ABC News contributor Col. Stephen Ganyard, who is a retired Marine Corps fighter pilot, says the kind of turbulence that the Singapore Airlines flight encountered was most likely what's known as clear-air turbulence. He also says if you're planning to fly for Memorial Day weekend, fear of turbulence shouldn't deter you from your plans.

Ganyard spoke with "Start Here," about turbulence in general, and what likely happened to Singapore Airlines flight SQ 321.

START HERE: Col. Ganyard, this was an international flight right? What happened here?

GANYARD: So let's talk about the facts as we know them now. It was a Singapore Airlines flight from London to Singapore. They had just come off the Indian Ocean, the Andaman Sea, and they were flying over Myanmar, over the Irrawaddy River valley, which is the north-south river within Myanmar. So, why is that important? Because it was hot. Tropical area. You have a river providing lots of moisture into the air. So hot, wet, rising air causes thunderstorms. We've seen the pictures of the area, both the radar returns and the overhead satellite returns. There was lots of major thunderstorm buildup in the area.

At some point, they hit turbulence. The turbulent incident resulted in a 100-foot drop and, just right after that, a 300-foot climb. So very rapid, negative G – negative G being less than gravity, meaning that's what you feel on a roller coaster, when you go over the top you feel that negative G. But it wasn't just zero G, it was one or two negative Gs, which would have forced people, slammed them onto the ceiling. And then as the airplane rapidly climbed up at those 300 feet, would have slammed them back down into the seats that they were supposedly supposed to be buckled into, or onto the cabin floor.

So it's that very rapid, unload negative G, throwing people up in the air, and then the positive G that came very quickly after that threw them back down to the ground. So there's two places where they get hurt: hitting the ceiling and coming back down to the ground.

START HERE: To look at the aftermath of this, I mean, there were images of, you had meals scattered all over the floor, debris everywhere. One passenger died of a suspected heart attack. Dozens more were injured. Some people are in critical condition. So how did this happen? One official described this is like a plane hitting an air pocket. I mean, what does that mean? How does turbulence work, I guess is what I'm asking you.

GANYARD: Yeah, don't ever say air pocket around me. I've trained you better.

START HERE: That's not a thing? Air pocket?

GANYARD: There's no such thing as an air pocket. Air is air, and air doesn't create pockets. But what people are talking about is that feeling of a drop. So we've had some of the passengers on board said, oh, we dropped thousands of feet. Well, this airplane did in fact descend – after this incident when people got hurt – several thousand feet. But it was a controlled descent.

But when you come back to turbulence, what is turbulence? The two primary kinds of turbulence are clear-air turbulence and convective turbulence, the turbulence that occurs in, say, thunderstorms or in big clouds, big lines of clouds. Clear-air turbulence is the kind of turbulence you get when, say, two jet streams come together. We know that the jet streams – you know, the pilots always talk about it, the meteorologists say the jet stream is pushing this weather across the country. So these are just big rivers of air between about 30,000 and 40,000 feet, that can be moving anywhere from 100 to 200 miles an hour.

When they run into each other, it's like two streams running together. So you see two rapids coming together. It creates additional turbulence. That can't be seen by radar on an airplane. So that is where the meteorologists before the flight come into play, where the meteorologists say, ooh, we see these two jet streams coming together, we see this area where there's potential for clear turbulence, and they'll brief the pilots before they even take off. So when the pilots get to a point in the journey where they say, we were told that there might be turbulence out here, they may preemptively flip on the fasten seatbelt.

So when we think about, well, what happened to the seatbelt sign? Apparently – and this is just a couple of reports from people on board the airplane – apparently that seatbelt sign went on only seconds before they hit the turbulence. Now, whether that was because the pilots didn't see anything on their radar or were just doing it as a precaution, or this was more clear air turbulence, which can't be detected by an airplane – that'll be a question for the investigators. But almost a certainty that anybody who was injured in this airplane was due to not having a seatbelt on at the time they hit that turbulence.

START HERE: I guess I'm trying to figure out how scared should we be going into, like, Memorial Day travel weekend? Because again, I mean, it sounds like so much force exerted on an aircraft so potentially quickly.

GANYARD: If you think about this, here's this airplane that went through this terrible turbulence, terrible injuries. But the airplane's fine. Airplanes that are carbon fiber, like the 787 or the A350: extraordinarily strong, the kind of material they're made out of is five times stronger than steel. So take comfort in the fact that this airplane went through this terrible, terrible set of turbulence and came out just fine because the airplane is designed to take it. If you have your seatbelt on, you're going to be fine. And Singapore Airlines is no fly-by-night airline. It is one of the best airlines in the world. They have great, airplanes, great, well-trained crews. And so if it can happen to Singapore, can happen to any airline in the world.

START HERE: All right. I guess I've got more confidence in seat belts, maybe even planes. But I'm going to need you there, sitting next to me, grabbing my hand if we go through turbulence like this. Colonel Stephen Ganyard, thank you so much.