Did a power bank start a fire on a recent Virgin flight? That’s the question investigators are currently trying to answer, as they probe an incident in Australia where a woman’s bag burst into flames.

The incident, which involved a flight from Sydney, took place around 9 a.m. on Monday, just as the plane was descending to its destination, the New York Times reports. After the bag burst into flames, the plane’s cabin filled with smoke, according to reports. The plane’s crew managed to put out the fire before the plane landed, the Times writes.

The newspaper notes that the fire is “believed to have been ignited by a portable battery inside the bag, although the cause remains under investigation.” A Virgin spokesperson told The Guardian: “Safety is always our highest priority. We appreciate the swift and professional response of our flight and cabin crew, as well as the support of Airservices Australia firefighters.” It’s unknown which power bank device was in the overhead bin. Gizmodo reached out to the airline for more information.

Power banks, portable chargers for your cell phone or other devices, have been the cause of many previous in-flight fires. They are often powered by lithium batteries, which, again, could be the culprit here. A fire at a Korean airport that took place in January was blamed on one such device. Virgin apparently told the Times that it was “reviewing its policy, which allows passengers to take power banks onboard, in light of the fire on Monday.”

Why do lithium batteries catch fire? Science tells us that batteries that overheat can “crack,” which then causes highly flammable liquid inside the battery to spill out and catch fire once exposed to the air.

Fires started by lithium batteries aren’t exactly a daily occurrence, but, more and more, they’re not exactly rare either. Recently released FAA data shows that in-flight fires spurred by the batteries have skyrocketed over the past ten years, spiking some 388 percent, according to one analysis. Since 2006, there have been 636 verified incidents involving lithium batteries, the agency says. A majority of those incidents have involved a battery pack, a cell phone, or a laptop, although a significant number have also involved e-cigarettes or vapes.