Ryanair CEO Michael O’Leary said on Monday that an initial finding from an investigation into a broken window incident earlier this month suggested “foreign object damage” and that the problem was caused by the aircraft’s age or servicing conditions.

“Initial indication would suggest it looks like a foreign object damage to the engine on takeoff at Thessaloniki, but we don’t have, we can’t say that definitively,” O’Leary told analysts after Ryanair’s results for the April-June quarter.

O’Leary said the aircraft was 18 years old and that the engine had been fully serviced and overhauled within the last two years.

He also said that a draft report on the incident would be released in under a month, with a more detailed report to follow.

On July 10, a piece of a Boeing 737’s engine broke off the aircraft and smashed into a window shortly after takeoff from Thessaloniki, Greece, en route to Memmingen, Germany, according to video footage and the Federal Aviation Administration.

The plane lost pressure and was forced to make an emergency landing.

A passenger was partly sucked out of the aircraft during the incident, but his wife and other passengers were able to grab him and pull him back inside.

The 61-year-old passenger was hospitalized after he suffered neck and shoulder injuries as well as friction burns.

Flight records show the aircraft, which was delivered new to Ryanair in 2008, had been climbing past 15,000 feet about six minutes after takeoff before then descending to about 6,000 feet. The aircraft remained at the lower altitude for about 30 minutes to burn fuel before returning to Thessaloniki about an hour after departure, according to flight-tracking site Flightradar24.

The National Transportation Safety Board is investigating the incident.

If damage to the aircraft was caused by an external object, it could reduce Boeing’s and Ryanair’s responsibilities in the incident.

Reuters contributed to this report.