ISLAMABAD: The Pakistan International Airlines allowed seven passengers to travel standing in the aisles all the way to Saudi Arabia last month, prompting a probe into the serious breach of security regulations by Pakistan's loss-making national carrier, according to media reports.As many as seven passengers aboard the Boeing 777 Pakistan International Airlines flight PK-743 ( Karachi-Madina ) on January 20 were forced to stand throughout the over three-hour flight after the airline boarded excess passengers, Dawn newspaper reported.The PIA management appears to have taken this lightly as no action has been taken against those responsible for the bizarre incident, the paper said.PIA spokesperson Danyal Gilani said the matter was being investigated.Gilani told the BBC that an internal investigation had begun "and appropriate action will be taken once responsibility is fixed".If someone was found responsible for any wrongdoing, the PIA would take stern action against them under the company rules, he said.The Boeing 777 aircraft has a seating capacity of 409, including jump seats for staff, while flight PK-743 carried 416 passengers from Karachi to Madina.The report said allowing seven passengers to travel by standing all the way to the destination constituted a serious air safety breach as in the case of an emergency, passengers without seats would not have access to oxygen and could also cause congestion in case of an emergency evacuation.The boarding passes issued to the extra passengers were hand-written and not computer-generated, sources said. The computer-generated list, provided to the aircraft crew by the ground traffic staff, did not mention the excess passengers, the report said.