About a month before the engine of a United Airlines Boeing 777 burst into flames last weekend after departing Denver International Airport, a Bombardier jetliner flying from Denver to Billings, Mont., declared an emergency when one of its engines failed shortly after takeoff. That plane landed safely 20 minutes after departure.
Nearly a year earlier, the crew of an Airbus 321 jet operated by American Airlines flying from Charlotte, N.C., to Philadelphia had to abort the flight when one of its engines quit after takeoff. Again, the plane landed safely, 13 minutes after takeoff.
And then there was the Feb. 3, 2020, Spirit Airlines flight from Fort Myers, Fla., to Chicago. Minutes after takeoff, passengers heard several loud bangs and saw streaks of flames from the disabled left-hand engine of the Airbus A320. The pilots landed the aircraft safely 15 minutes into the flight.
These and other recent examples of midflight engine failures — including the latest mishap of the Boeing 777 now being investigated by the National Transportation Safety Board — demonstrate the ability of modern commercial airliners to fly for an extended period even after one engine quits.
Aviation records over the last 24 months show nearly two dozen reports of U.S.-based commercial planes aborting flights because of an engine failure or because the crew shut down an engine due to mechanical problems. In each case, the planes landed safely with one engine out of commission.
Some of the larger commercial jets fly with four engines, and they can continue with only three if needed. But even on two-engine commercial planes, each individual engine has enough thrust to continue flying the whole plane for long distances, according to aviation experts.
“The overall system is designed with the knowledge that man-made components are going to fail occasionally,” said Clint Balog, an associate professor at Embry-Riddle Aeronautical University.
And pilots train regularly for such a mishap.
“We spend a lot of time in single-engine training,” said R.D. Johnson, a former fighter pilot and retired American Airlines captain who now flies corporate jets. “It’s pretty innate for an experienced pilot.”
That was made clear during the United Airlines flight of a Boeing 777, which was en route Saturday from Denver to Honolulu with 229 passengers and 10 crew members. Just as the plane was reaching an altitude of 12,500 feet, the crew and passengers heard a loud bang and felt the plane vibrate, according to investigators. The pilots declared an emergency, turned the plane around and landed back in Denver 20 minutes later.
Parts of the shell containing the engine disintegrated and fell to the ground, with some pieces landing in front yards and a soccer field. Inspectors found minor damage to the wing, but NTSB Chairman Robert Sumwalt told reporters this week it did not appear that any structural damage was caused by fragments that flew out of the engine.
NTSB inspectors are focusing their investigation on two fan blades in the engine that appear to have fractured due to metal fatigue, leading to the damage to the engine’s containment unit.
The Federal Aviation Administration has ordered increased inspections of the fan blades on Pratt & Whitney 4000 series engines, the type used in that plane.
Boeing recommended over the weekend the worldwide suspension of operations of the 69 in-service and 59 in-storage 777s using the same Pratt & Whitney engines until further notice. Federal officials said that only the U.S., South Korea and Japan use planes with the Pratt & Whitney 4000 series engine. In the U.S., only United flies with that engine. Airlines grounded the plane pending an investigation.
The incident was the latest of several similar mishaps involving Pratt & Whitney engines on Boeing 777s.
On Feb. 13, 2018, a 777 flying United Airlines passengers from San Francisco to Honolulu experienced a failure of the same type of engine over the Pacific. The plane landed safely in Honolulu. The NTSB concluded that a fan blade inside the engine fractured, leading to the failure.
A Dec. 4 Japan Airlines flight of a 777 also suffered a failure of the same type engine on a trip from Okinawa to Tokyo. Part of the engine cover and a fan blade were damaged. The plane landed safely in Okinawa.
Pratt & Whitney said in a statement Tuesday that it’s cooperating with regulators, airlines and Boeing and that safety “is our top priority.”
As for the plane that made its emergency landing last weekend, Sumwalt said its damaged parts and maintenance history would be examined. The cockpit flight recorder has been taken to Washington, D.C., for examination, he said.
“We are going to be very deliberate about going through the inspections and all the maintenance records,” Sumwalt said.
Pilots who have flown planes that suffered an engine failure say controlling a one-engine plane requires a lot of training and a bit of finesse.
“The general issue is controllability,” said Doug Moss, a retired test pilot and retired captain at United Airlines. He said that when working for United, he once had to shut down an engine of a Boeing 727 plane because the throttle was stuck.
With one engine operating and the other shut down, Moss said, the plane wants to “skid sideways.”
He said he had to counter that by engaging the rudder but in very measured amounts.
“It’s a skill set,” Moss said. “You have to use a lot of muscle memory. It’s like dribbling a basketball. You have to do it a couple of hundred times before you get it.”
