A pilot will choose to dump fuel only on very rare occasions.

In the case of an emergency situation the flight crew can decide to dump, dirty up the plane or land heavy.

The dumped fuel evaporates before it hits the ground.

Visit Business Insider's homepage for more stories.

Following is a transcript of the video.

Narrator: On March 23rd, 2018, a 60-year-old woman on a flight from Shanghai to New York began having trouble breathing. When she started slipping in and out of consciousness, the pilot knew there was only one thing to do to save her: dump more than 65,000 pounds of fuel into the sky. The flight then made an emergency landing in Anchorage, Alaska, where the passenger recovered in a local hospital, but how did draining almost $20,000 worth of jet fuel save her life?

Anthony Brickhouse: Fuel dumping, simply explained, is an aircraft losing weight before it lands.

Narrator: Anthony is an Associate Professor at Embry-Riddle Aeronautical University. And what he's talking about is officially called a fuel jettison. Planes are designed to land below certain weights. A heavier plane is more likely to hit the ground hard and get damaged. It's got 5,000 gallons of fuel, which is about three elephants weighing it down. So, landing with a full tank is pretty risky. But most flights aren't landing with a full tank. They might not be taking off with a full tank either. Before takeoff, the flight planner calculates the amount of fuel needed to complete the trip. So that enough fuel gets burned off over the course of the flight and the plane's weight comes down and then it's safe to land. A pilot will choose to dump fuel only on very rare occasions.

Brickhouse: Unless you have a medical emergency on board, someone is dying, you don't really have time to fly around and burn fuel. So, in that case that's when you would dump fuel so that you can lose weight quickly.

Narrator: If the pilot has a little more time or doesn't have the capacity to dump fuel like in a lot of smaller crafts, they might dirty up the plane, this means purposefully creating drag and flying around in circles in order to burn off the excess fuel. But if a passenger is critical, like the woman from 2018, they might not have time for that. Fuel jettisoning systems can dump thousands of pounds a second. Most can get a plane back down to its max landing weight in 15 minutes or less, and it's usually as easy as flipping a switch in the cockpit. Most systems are a series of pumps and valves that divert the fuel to the tips of the wings. The fuel streams behind the plane in what looks like contrails and yes, there is a fail-safe in place to stop the pilot from expelling all the fuel at once. But it's not just a pilot's judgment that decides when and how fuel gets dumped.

The Federal Aviation Administration has a handful of regulations in place: the plane has to be at least 2,000 feet above the highest obstacle along the route, at least five miles from any other aircraft and away from populated areas and bodies of water whenever possible. But aside from this page of FAA policy, that's about it when it comes to regulations. Dumping fuel into the atmosphere isn't free of consequences, but the Environmental Protection Agency just isn't worried about it. It regards the practice as exceedingly rare and leans into the fact that airlines don't promote it because it's a waste of money.

Brickhouse: If we get to a point where we're seeing more aircraft with the capability to dump fuel and we're seeing more aircraft dumping fuel and maybe not from an emergency point of view, then maybe yes, that would be something that the EPA would need to look into.

Narrator: British Airways estimated in 1999 that only .01% of fuel used by the aviation industry each year is dumped. If that number still holds up today, we're looking at almost two million gallons dumped in 2018 by U.S. airlines alone. Dumped jet fuel is supposed to evaporate before it hits the earth, but even Boeing has said that "Even though fuel is vaporized, "it is still suspended in the atmosphere. "And the fuel will eventually reach the ground." The U.S. Agency for Toxic Substances and Disease Registry listed mixed results in regards to the biodegradability of jet fuel, and the same study went on to say, it can be transported by wind and become a component of smog.

So, other than burning it off, are there any more alternatives to fuel dumping? It is possible to land an overweight plane. It happens every once in a while but it's not recommended. The Flight Safety Foundation lists almost 300 airplane safety incidents from the beginning of the 1900s to now that include landing heavy as a contributing cause. Whenever it happens, the plane stays grounded for a lengthy inspection before it's allowed to fly again.

Brickhouse: But if you land heavy, obviously, you could actually overstress the aircraft which can cause immediate damage or it could cause damage that actually presents itself down the line on a totally different flight.

Narrator: No matter if a flight crew decides to dump dirty or land heavy, each option has its pros and cons. But in any emergency situation, your job as a pilot is to get the craft down to the ground as quickly as possible and as safely as possible and if that means landing heavy, then that's just a decision that's going to have to be made. In some situations you really don't have a choice, you have to get down. Ultimately, it comes down to keeping passengers safe.