It feels like a nightmare scenario for plane travellers: You acquire a glimpse out the window in among mini-pretzel bites to see an engine cloaked in flames, shedding pieces of metal mid-flight from 10,000 ft in the air. Which is specifically the sight that greeted travellers of United Flight 328 on Saturday not extensive just after departing Denver for Honolulu.

A around 500,000-pound jet with a person motor appears to be as likely a candidate to fly as a condor with 1 wing. And nevertheless for all the risk posed by the flambé Boeing 777 this weekend—and there was a great deal, especially to the Denver suburbs subjected to large-scale debris lose by the plane’s Pratt & Whitney PW4077 engine—staying in the air was really reduced on the list. In simple fact, its remaining motor is theoretically potent enough to have made the remainder of the flight on its have.

That wasn’t generally the scenario for big plane. For many years, the Federal Aviation Administration didn’t allow for twin-engine planes to make outings around an hour, a lot significantly less from the Midwest to a Pacific paradise. “It’ll be a cold working day in hell just before I enable twins fly extended-haul about-drinking water routes,” then-FAA administrator Lynn Helms insisted when Boeing requested the FAA to transform the rule in 1980, according to Robert J. Sterling’s 1991 heritage of the aerospace huge. If an engine did are unsuccessful, you’d have at the very least two other people to rely on.

Eventually the FAA relented, growing the 60-moment rule to 120 and then 180 minutes as the ’80s wore on. Credit score enhanced engines for the change of heart, relatively than an elevated hunger for threat.

Travellers on United Flight 328 have been alarmed to obtain the still left motor had caught fire a few minutes soon after takeoff.

Photograph: Chad Schnell/Getty Photographs

“One engine has to have plenty of thrust to continue to keep the plane likely, and even climbing if it requirements to,” suggests Ella Atkins, an aerospace engineer at the College of Michigan. That applies even to a worst-situation scenario, she suggests, this sort of as shedding an engine while you are in the approach of having off. The remaining motor requires to be potent adequate, if necessary, to get you airborne on its have.

Which is not to say that engine failure is without the need of consequence, particularly when a fireplace is involved. It introduces a host of troubles no matter the measurement of the aircraft or the complexity of its automatic methods. “Many pilots go via their total occupation with out a solitary engine failure, even though we teach for it,” says Bob Meder, chairman of the National Association of Flight Instructors. “In general, you do your memory objects very first for the airplane you’re flying. You’ve acquired an engine fire, you secure the engine and quit the circulation gasoline to the motor.”