It’s seven years late and has racked up over $15 billion in charges, but Boeing’s most important plane is expected to finally fly passengers in 2027.

Over a dozen airlines are waiting on the yet-to-be-certified Boeing 777X, the world’s largest twin-engine widebody in production, packed with more than 400 seats and capable of flying up to 9,000 miles nonstop.

Boeing says the wider cabin, longer wings with folding wingtips, and giant General Electric engines create more seat room, open new routes, and provide a more efficient and comfortable flying environment compared with the planes it’s replacing.

After years of delays, Boeing executives…