Detectives are planning to fly to Glasgow to interview Celtic football fans about an alleged mid-air "riot" on a 737 jet.
Six soccer fans were arrested when the pilot of the jet sent out a Mayday call and the plane was diverted to Cardiff International Airport on Friday.
All six, aged between 37 and 51, were released on bail but have to report back to Barry police station, south Wales, next March.
The Astraeus Boeing 737 was returning to Glasgow from Santiago, Spain, where Celtic had beaten Celta Vigo in a UEFA Cup tie on Thursday evening.
The remaining 142 passengers aboard were later bussed back to Scotland.
Some claimed the authorities had over-reacted to the incident and said nothing resembling a riot had occurred.
But South Wales Police superintendent Colin Jones has dismissed criticism, saying the mid-air incident is being treated as "extremely serious".
"Detectives will be flying to Glasgow to pursue this investigation but no date has yet been set," a South Wales Police spokeswoman said.