Airline staff on a flight to Brazil were stunned to find a bullet lodged in the wing
Maintenance staff discovered a bullet clearly embedded in the plane's bodywork and say it could have caused a fatal crash if it had struck electrics or a fuel line.
Police are investigating whether someone on the ground deliberately aimed at the Boeing 767-300 or whether it was an accident.
One report suggests there may have been a rifle competition on a range under the aircraft's flight path although there have been reports of gangs in Brazil aiming at planes "just for fun".
Another theory is that there might have been a shoot-out between rival drugs gangs on Brazilian soil and a bullet could have gone astray.
The Latam Boeing was flying from Spain to Sao Paulo Guarulho in Brazil in what the crew and passengers thought was an uneventful flight.
Maintenance staff discovered a bullet clearly embedded in the plane's bodywork
It was only during routine maintenance work that a hole was discovered in the flap of the left hand wing with a bullet embedded in it. The 7.62mm caliber projectile was still clearly visible, having penetrated the bodywork.
Neither crew nor passengers noticed anything abnormal
According to the Aviation Herald, it was not possible to determine at which stage of the last commercial flight from Barcelona to Sao Paulo the bullet struck the aircraft.
The Latam Boeing was flying from Spain to Sao Paulo Guarulho in Brazil
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"Neither crew nor passengers noticed anything abnormal," said the official report.
Experts said the bullet did not compromise the safety of the flight.
Latam Airlines flies regularly to Brazil, Argentina, Peru, Colombia, Chile and Ecuador.