A domestic flight of Japan’s All Nippon Airways (ANA) has returned to its departure airport after a crack was reported on the cockpit window of the Boeing 737-800 aircraft midair, an airline spokesperson says. Flight 1182 was en route to Toyama airport on Saturday but headed back to the Sapporo-New Chitose airport after the crack was found on the outermost of four layers of windows surrounding the cockpit.

The spokesperson said there were no injuries to anyone on board. ANA flight NH1182 was flying from the city of Sapporo in Hokkaido to Toyama, on Japan’s main island, Honshu. The plane, a Boeing 737, landed back at Sapporo’s New Chitose airport at around 12.10 p.m. local time, the BBC reported.

A spokesperson for ANA, Japan’s largest carrier, said that the crack had been found as the flight passed over Hakodate. “The crack was not something that affected the flight’s control or pressurisation,” the spokesperson said.

The plane headed back to the airport where a safe landing was carried out, BBC reported. Aviation expert John Strickland said the cause of the crack was still unknown. There were 59 passengers and six crew members on board. Alternative flights were arranged for the passengers.

This is the second incident involving a Boeing 737 model aircraft in as many weeks. However the ANA flight was not one of Boeing’s 737 MAX 9 airplanes, but an earlier version which was “by no means old”, Strickland said.

All Boeing 737-9 aircraft have been grounded by the US aviation regulator the FAA after an Alaska Airlines plane suffered a blowout that saw a cabin panel fall off a new plane in mid-air, leaving a gaping hole in the side of its fuselage last week, BBC reported. That plane, carrying 177 passengers and crew, had to make an emergency landing in the US state of Oregon.