Two Yakovlev Yak-52 planes collided in mid-air during a demonstration at Portugal’s Beja Air Show on Sunday, resulting in a deadly crash that killed one pilot, the country’s air force said, Paralel.Az reports citing The Daily Beast.

“The air force regrets to announce that at 4:05 pm (1505 GMT), at the Beja Air Show, two planes were the victim of an accident during an aerial demonstration,” it said in a statement.

Video from the incident appeared to show one aircraft that broke away from the formation making a sudden, sharp climb that struck the lead aircraft head-on. The climbing aircraft appeared to lose control and abruptly plummet to the earth, as the aircraft that was struck made a quick but apparently controlled descent to land.

According to the flight safety database Aviation Safety Network, the pilot of the climbing aircraft lost control and was killed in the crash, which resulted in a post-impact engine fire. The pilot of the other aircraft managed a landing some ways away. The death was not confirmed by the Portuguese air force.

Both planes were part of the six-aircraft Spanish-Portuguese Yakstars team. The team was flying as part of a planned exhibition at the Beja Air Show in southern Portugal, which advertised “world class aerial performances” and rare aviation feats, according to the European Airshows website.

It was not immediately clear what caused the rogue aircraft to break away from the group, or if its sudden climb was a botched part of a planned maneuver.