Boeing has confirmed that it has grounded over 50 of its planes around the world, after wing-related cracks were discovered, while the company’s CEO has admitted to making safety mistakes.

It’s the US aviation giant’s 737NG (Next Generation) model that is now under scrutiny. It’s a precursor to the infamous Boeing 737 MAX, which killed 346 in two crashes in Indonesia and Ethiopia, and has been grounded since March.

Boeing spokesperson told AFP that some 1,000 planes worldwide had “reached the inspection threshold”. The problem these inspections zeroed in on was the so-called ‘pickle fork’ – a part of the plane that connects the fuselage to the wing.

The US aviation authority this month ordered checks of Boeing 737NG planes that had made over 30,000 flights.

Meanwhile, the company’s CEO was testifying before a US House panel on Wednesday, where he said the company made some mistakes on the key-safety system known as MCAS.

“I am responsible. These two accidents happened on my watch. I feel responsible to see this through,” Dennis Muilenburg admitted, refusing to step down.

Two deadly crashes involving Boeing’s newest 737 MAX 8 airplane in less than six months puts the credibility of the manufacturer in jeopardy. The fatal Ethiopian Airlines accident claimed 157 lives in March followed a similar crash in Indonesia, which killed all 189 people on board in October.