A Qantas Airways Ltd. A380 superjumbo suddenly lost altitude for about 10 seconds more than 30,000 feet above the Pacific Ocean after flying through the wake of another plane.

Flight QF94, two hours after taking off from Los Angeles to Melbourne on the night of June 10, plunged upon hitting the wake turbulence of another Qantas A380 that was on its way to Sydney, the Australian airline said in a statement. No injuries were reported. The planes were separated by 20 nautical miles and 1,000 feet in altitude.

According to one of the passengers, Australian radio host Eddie McGuire, QF94 dropped and turned slightly, almost like going over the top of a roller-coaster. After leveling off, the captain explained what had happened and said the crew had asked for a different flight path, McGuire said on the radio on Thursday.

An aircraft’s wake turbulence consists of two vortexes spinning in opposite directions, and large and relatively slow-moving planes produce the most powerful forces, according to Australian aviation authorities. In the right conditions, the vortexes can hang around for more than three minutes. Unrecoverable induced rolls are among the biggest risks to nearby planes.

Safe Distance

It’s tough to completely eliminate the risks from wake turbulence, Qantas Fleet Safety Captain Debbie Slade said in the airline’s statement.

“Aircraft are designed to handle it safely,” Slade said. “We always recommend passengers keep their seat belt firmly fastened at all times just as pilots do in the flight deck.”

The Australian newspaper cited a passenger on QF94, who described a 10-second freefall about two hours into the flight.

“It was an absolute sense of losing your stomach and that we were nosediving,” Janelle Wilson told the newspaper. “The lady sitting next to me and I screamed and held hands and just waited but thought with absolute certainty that we were going to crash. It was terrifying.”

Flying into the vortexes can be like hitting a wall, according to a wake turbulence guide by the Federal Aviation Administration. Between 1983 and 1993, there were at least 51 accidents and incidents in the U.S. from probable encounters with wake turbulence. Those incidents killed 27 people and damaged or destroyed 40 aircraft, the FAA said.

The two Qantas jets, which both took off from Los Angeles, were on flight paths assigned by U.S. controllers and were flying at a safe distance, said a spokesman for Qantas. Australia’s air-safety authority said Thursday it has reviewed Qantas’ report on the incident and it’s not opening an investigation.