AirlineRatings.com has downgraded Sri Lankan’s safety rating from seven to six stars after one of its captains allegedly locked his female copilot out of the flight deck during a 10-hour flight from Sydney to Colombo aboard an Airbus A330.

According to Aviation Herald (AV) the incident occurred on a Sri Lankan Airbus A330-300, registration 4R-ALR performing flight UL-607 from Sydney, (Australia) to Colombo (Sri Lanka), and was enroute when the first officer left the cockpit for a toilet break.

The captain locked the door and refused to let the first officer back in. The aircraft continued for a safe landing in Colombo.

AV reported that the first officer filed a complaint after landing indicating that a disagreement between the captain and herself had caused the lockout.

The airline has said that the captain has been grounded while Sri Lanka's Civil Aviation Authority have opened an investigation.

According to other media the situation escalated to the point where a senior cabin crew member had to intervene, using the communication system to persuade the captain to unlock the door and allow the copilot to return to her seat.

AirlineRatings.com deems this incident extremely serious and has downgraded Sri Lankan Airlines’ safety rating.