A Southwest Airlines flight headed to Las Vegas on Friday abruptly dropped 500 feet midair soon after takeoff from a Los Angeles-area airport, as onboard alerts warned pilots that another plane was nearby, according to federal authorities and the airline.

Six minutes after taking off from Hollywood Burbank Airport, Southwest Airlines Flight 1496 reached an altitude of 14,100 feet. It then dove to 13,625 feet in a 33-second maneuver, according to data from Flightradar24. The plane climbed to 14,225 feet over the next 26 seconds.

People flew out of their seats and hit their heads on the ceiling, according to Jimmy Dore, a stand-up comedian who said he was on the plane. Two flight attendants were injured.

The flight landed in Las Vegas without further incident, according to Southwest, which said in a statement that the plane was responding to two onboard traffic alerts. The airline said it was engaging with federal authorities “to further understand the circumstances.”

No passengers immediately reported injuries, it added.

The airline could not be reached for additional comment late Friday.

The Federal Aviation Administration said in a statement that the Southwest Airlines flight was responding to “an onboard alert that another aircraft was in the vicinity.” The agency is investigating the event and said its initial findings were “preliminary and subject to change.”

At the time of the event, a Cold War-era military aircraft was headed to Point Mugu Naval Air Station, according to Flightradar24. The Hawker Hunter MK58 was about four miles away from the Southwest plane, and 400 feet above it, before Southwest Flight 1496 dropped 500 feet.

The Washington Post could not immediately verify whether this plane was what led the Southwest flight to take evasive action.

The episode comes after a passenger jet landing in North Dakota performed a “go-around” to avoid colliding with an Air Force B-52 last week. In March, a Delta flight departing Reagan National Airport near D.C. was diverted to avoid a potential collision with a group of Air Force jets. In January, an Army Black Hawk helicopter and a passenger jet collided near National Airport, killing 67 people.