An investigation launched after seven extra passengers allegedly boarded a Pakistan International Airlines flight from Pakistan to Saudi Arabia in January.

The passengers reportedly used handwritten boarding cards to gain access to the plane and stood in the aisle for the duration of the three-plus-hour-long flight. Officials are seeking to find out how staff allowed the flight on Jan. 20, to take off with 416 passengers when it’s only permitted to carry 409. This incident constituted as a serious air safety breach since the extra passengers wouldn’t have access to oxygen in case of emergency.

“After takeover when I came out of the cockpit, Ms. Turab informed me that there were some extra people who [had been] boarded by the traffic staff. I also noticed some people were those who were categorically refused jump seats by me at the check-in counter before the flight,” said Anwer Adil, the flight’s captain. “I had already taken off and the senior purser did not inform me about extra passengers before closing the aircraft door.”

Adil said his official passenger list didn’t indicate any extra passengers and by the time he found out, it was too late. Instead of reversing course, the flight continued on to Medina (MED).

The matter is under investigation and appropriate action will be taken once responsibility is fixed.