United Airlines flight 1175 bound from San Francisco to Honolulu, Hawaii, ran into some major mechanical trouble as the aircraft had on their engines blow off mid-way through the flight. It’s not exactly clear what caused this to occur according to the Federal Aviation Administration, but investigations are under way.

Per the New York Times,

Passengers heard a loud bang and felt the plane shake violently. Those seated on the right side looked out their windows and saw pieces of metal flying. By the time the plane touched down safely in Honolulu around 40 minutes later, the engine was bare, its innards on full display.

Similar malfunctions have happened before. In 2016, an American Airlines flight from Phoenix to San Francisco turned back after part of the engine cowling fell off. A JetBlue flight from Newark to Fort Lauderdale, Fla., did the same in 2010. And an Air France flight had to make an emergency landing in northern Canada last year after one of its engines exploded in midair.

United issued the following statement:

United flight 1175 traveling to Honolulu from San Francisco landed safely after the pilots called for an emergency landing because of an issue with the #2 engine. Our pilots followed all necessary protocols to safely land the aircraft. The aircraft taxied to the gate and passengers deplaned normally.