Ryanair chief executive Michael O’Leary should refrain from commenting on the investigation into an accident in which a passenger was almost sucked out of a damaged aircraft window, the organisation leading the inquiry has warned.A Boeing 737-8AS operated by Ryanair Holdings subsidiary, Malta Air, had to return to Thessaloniki Airport recently after parts from a damaged engine hit a window.O’Leary told analysts this week that initial findings from the investigation indicated that it resulted from “foreign object damage” not the plane’s age or servicing.However, Jennifer Homendy, chairwoman of US National Transport Safety Bureau (NTSB), which is running the inquiry, warns that the airline chief should “refrain from further public statements regarding the investigation while it is ongoing”, in a letter sent on Wednesday.Ryanair is a technical adviser to the investigation so is obliged to take all reasonable steps to ensure information relating to it is protected from public release, Homendy states.“The NTSB has not made any such determination, and our investigators have not yet ruled out age or servicing issues as contributing to this event,” she adds.[ Ryanair’s profits take €292m hit amid fallout from Iran warOpens in new window ]News agency reports of O’Leary’s remarks, made on Monday to investors’ analysts after Ryanair published financial results, prompted Homendy’s rebuke. Ryanair did not comment.The UN International Civil Aviation Organisation designated the NTSB as the lead investigator of the incident, which occured on a flight from Thessaloniki, Greece to Memmingen, Germany on July 10th.Pressure was lost in the cabin while oxygen masks were dropped as a precaution, passengers said afterwards.Ryanair said in a statement issued after the incident that the aircraft “returned to Thessaloniki shortly after takeoff when a passenger window dislodged in flight”.“The aircraft landed normally and passengers returned to the terminal,” it added.Separately, Ryanair announced plans on Thursday to spend €50 million expanding its maintenance operation in Shannon Airport, creating more than 400 jobs.Aer Lingus job cuts and Ryanair’s profits plunge - what is happening in the Irish aviation sector? Listen | 41:54The airline is seeking planning permission to expand engineering at Shannon to make it Ryanair’s largest aircraft maintenance facility in Ireland.The €50 million investment will include a new four-bay maintenance, repair and overhaul hangar and an engineering academy, which will train more than 400 aircraft mechanics between 2027 and 2031, the airline said.Subject to planning permission, Ryanair hopes to begin construction early next year and open the facility in late 2028.Ryanair already operates a three-bay hangar. The new one will be key to ongoing investment in aircraft maintenance and engineering training across its network, the airline noted.[ Michael O’Leary’s mega pay-day may hinge on proving Ryanair can thrive without himOpens in new window ]The expansion will create “hundreds of highly skilled engineering jobs while training the next generation of aircraft mechanics”, said Eddie Wilson, chief executive of Ryanair DAC, the group’s biggest subsidiary.Ryanair’s investment in skills and training in Shannon “is particularly significant” said Jenny Melia, chief executive of Enterprise Ireland, which is supporting venture.The airline’s proposal reflects the depth of aviation expertise and engineering capability that has developed in Shannon over the decades, Shannon Airport Group chief executive, Ray O’Driscoll pointed out.Minister for Enterprise, Tourism and Employment, Peter Burke, said the Government was committed to supporting the development of Irish multinationals.